GEOLOGY IN CIVIL ENGINEERING
Geology and Civil Engineering Relationship
Civil engineering works are carried out either on site
or within the site.
For this reason, erosional and geological process
which cause the stability of the rocks and ground and their
changes are important for civil engineering.
Where is a geologically safe and economical engineering
structure built?
• How to choose the communication and transport
infrastructure route where geological conditions are
convenient?
• How are the building bases constructed safely and
economically
in
terms
of
geological and
geotechnical aspects?
• How to create a slope both safely and
economically?
• How is a safe tunnel and underground facility
excavation done?
• How are location geological materials required for
construction of dams and road construction
determined?
• What are the measurements and application
methods for improvements of ground conditions and
controlling instability, infiltration etc.?
• What are required geological and geotechnical
conditions store urban, toxic and radioactive waste?
• How are to identify, prevent or reduce geological
hazards identified, prevented and reduced?
Importance of Geology for Civil Engineering
1. The role of geology in civil engineering may be briefly
outlined as follows: 1. Geology provides a systematic
knowledge of construction materials, their structure
and properties.
2. The knowledge of Erosion, Transportation and
Deposition (ETD) by surface water helps in soil
conservation, river control, coastal and harbor
works.
3. The knowledge about the nature of the rocks is very
necessary in tunneling, constructing roads and in
determining the stability of cuts and slopes. Thus,
geology helps in civil engineering.
4. The foundation problems of dams, bridges and
buildings are directly related with geology of the
area where they are to be built.
5. The knowledge of ground water is necessary in
connection with excavation works, water supply,
irrigation and many other purposes.
6. Geological maps and sections help considerably in
planning many engineering projects.
7. If the geological features like faults, joints, beds, folds,
solution channels are found, they have to be suitably
treated. Hence, the stability of the structure is greatly
increased.
8. Pre-geological survey of the area concerned
reduces the cost of engineering work.
Branches of Geology
1. Physical Geology. As a branch of geology, it deals
with the “various processes of physical agents such
as wind, water, glaciers and sea waves”, run on
these agents go on modifying the surface of the
earth continuously.
-Physical geology includes the study of
Erosion, Transportation and Deposition (ETD).
-The study of physical geology plays a vital
role in civil engineering thus:
a.
It reveals constructive and destructive processes of
physical agents at a particular site.
b.
It helps in selecting a suitable site for different types
of project to be under taken after studying the effects of
physical agents which go on modifying the surface of the
earth physically, chemically and mechanically.
2.
Crystallography. As a branch of geology, it deals
with ‘the study of crystals. A crystal is a regular polyhedral
form bounded by smooth surfaces. The study of
crystallography is not much important to civil engineering, but
to recognize the minerals the study of crystallography is
necessary.
3.
Mineralogy. As a branch of geology, it deals with the
study of minerals. A mineral may be defined as a naturally
occurring, homogeneous solid, inorganically formed, having
a definite chemical composition and ordered atomic
arrangement.
-The study of mineralogy is most important:
a.
For a civil engineering student to identify the rocks.
b.
In industries such as cement, iron and steel, fertilizers,
glass industry and so on.
c.
In the production of atomic energy.
4.
Petrology. As a branch of geology, it deals with the
study of rocks. A rock is defined as “the aggregation of
minerals found in the earth’s crust”. The study of petrology is
most important for a civil engineer, in the selection of suitable
rocks for building stones, road metals, etc.
5.
Structural Geology. As a branch of geology, it deals
with the study of structures found in rocks. It is also known as
tectonic geology or simply tectonics.
-Structural geology is an arrangement of
rocks and plays an important role in civil engineering
in the selection of suitable sites for all types of
projects such as dams, tunnels, multistoried buildings,
etc.
6.
Stratigraphy. As a branch of geology, it deals with
‘the study of stratified rocks and their correlation’.
7.
Paleontology. As a branch of geology, it deals with
‘the study of fossils’ and the ancient remains of plants and
animals are referred to as fossils. Fossils are useful in the study
of evolution and migration of animals and plants through
ages, ancient geography and climate of an area.
8.
Historical Geology. As a branch of geology, it
includes “the study of both stratigraphy and paleontology”.
Its use in civil engineering is to know about the land and seas,
the climate and the life of early times upon the earth
9.
Economic Geology. As a branch of Geology, it deals
with “the study of minerals, rocks and materials of economic
importance like coal and petroleum”.
10.
Mining Geology. As a branch of geology, it deals
with “the study of application of geology to mining
engineering in such a way that the selection of suitable sites
for quarrying and mines can be determined”.
11.
Civil Engineering Geology. As a branch of geology, it
deals with “all the geological problems that arise in the field
of civil engineering along with suitable treatments”. Thus, it
includes the construction of dams, tunnels, mountain roads,
building stones and road metals.
12.
Hydrology. As a branch of geology, it deals with “the
studies of both quality and quantity of water that are present
in the rocks in different states” (Conditions).
- Moreover, it includes:
a.
Atmospheric water,
b.
Surface water, and
c.
Underground water.
13.
Indian Geology. As a branch of geology, it deals with
“the study of our motherland in connection with the
coal/petroleum, physiography, stratigraphy and economic
mineral of India”.
14.
Resources Engineering. As a branch of geology deals
with “the study of water, land, solar energy, minerals, forests,
etc. fulfil the human wants”.
15.
Photo Geology. As a branch of geology deals with
“the study of aerial photographs”.
EARTH STRUCTURE AND COMPOSITION
THE INTERIOR OF THE EARTH
Direct Observations
The observed temperature few centimeters away from the
surface is about 20°C, however, as we move further away
from the surface, the temperature would increase by C°
every 100 m. In which the
estimated temperature at a depth of about 2500 m the rocks
would be hot enough to boil water –
almost 100°C.
THE STRUCTURE OF EARTH
The earth’s structure is metaphorically compared to a hardboiled egg, it has a hard, crusty, and a but
brittle shell, but as it is divided in half, it will expose its different
layers inside. In a more realistic representation, we do not
and certainly cannot cut the planet in half but through
various natural
phenomenon, we are able to take a few glimpses of its
insides, and most commonly through an active
volcano.
A volcanic eruption as we all know is the way the insides of
the planet releases its excess pressure and
steam, and with that often times, expelled not only steam but
as well as lava, giving us enough evidence to conclude that
there is a vast load of molten rocks underneath the earth’s
livable surface.
Earth’s rocky crust is by no means stationary and we regularly
see evidence of crust movement in the
form of earthquakes. Earthquakes in ocean regions produce
destructive ocean waves called ‘tsunamis. The universal
acceptance of plate tectonic theory is recognized as a
major milestone in the earth sciences. It is comparable to the
revolution caused by Darwin’s theory of evolution or Einstein’s
theories about motion and gravity. Plate tectonics provide a
framework for interpreting the composition, structure, and
internal processes of Earth on a global scale. Earth is made of
three concentric layers: the core, mantle, and crust. Each
layer has its own chemical composition and properties (see
Figure 1).
The core has two layers: an inner core that is solid and an
outer core that is liquid. The core is mostly
iron, with some nickel and takes up 16% of Earth’s total
volume. The metallic core accounts for Earth’s
magnetic field. Earth behaves as though it has a simple
straight bar magnet at its center, with the ‘south’pole just
below Canada and the ‘north’ pole opposite, not quite
coincident with the geographical poles (see Figure 2). A
compass needle’s ‘north’ pole points northwards; because
‘unlike’ poles attract, Earth’s magnetic pole in the Arctic must
be the opposite type, ‘south’. It is thought that streams of
liquid metal within the outer core, combined with Earth’s
rotation, cause the magnetism. The strength of the
magnetism may change from decade to decade and, over
the period of 500 000 years, the magnetism reverses
completely. This means that over the next 500 000 years,
compasses will point south! Evidence of Earth’s change in
magnetic polarity (direction of north–south line of
magnetism) is found in the rocks. Scientists have found that
rocks within Earth’s crust formed at different times. Within
some rocks there are small particles of magnetite that are
magnetic and, when the rocks were formed, these
magnetite particles aligned themselves with Earth’s magnetic
field. As the rocks cooled, the direction of the particles’
magnetic polarity was fixed. Therefore, by knowing the age
of a rock and the magnetic polarity of the magnetite
particles within it, we can determine the magnetic polarity
and Earth’s strength in times past.
Outer Core
The outer core, about 2,200 kilometers (1,367 miles) thick, is
mostly composed of liquid iron and nickel.
The NiFe alloy of the outer core is very hot, between 4,500°
and 5,500° Celsius (8,132° and 9,932°
Fahrenheit). The liquid metal of the outer core has very low
viscosity, meaning it is easily deformed and
malleable. It is the site of violent convection. The churning
metal of the outer core creates and sustains
Earth’s magnetic field.
Inner Core
The inner core is a hot, dense ball of (mostly) iron. It has a
radius of about 1,220 kilometers (758 miles).
Temperature in the inner core is about 5,200° Celsius (9,392°
Fahrenheit). The pressure is nearly 3.6
million atmosphere (atm). The temperature of the inner core
is far above the melting point of iron. The
pressure and density are simply too great for the iron atoms to
move into a liquid state
FIGURE 2: EARTH AS A MAGNET
FIGURE 1: INTERIOR STRUCTURE OF EARTH
COMPOSITIONAL LAYERING
CORE
MANTLE
The mantle is the thickest of Earth’s layers and takes up 83% of
Earth’s volume. It extends down to
about 2900 km from the crust to Earth’s core and is largely
composed of a dark, dense, igneous rock
called ‘peridotite’, containing iron and magnesium. The
mantle has three distinct layers: a lower, solid
layer; the asthenosphere, which behaves plastically and flows
slowly; and a solid upper layer. Partial
melting within the asthenosphere generates magma (molten
material), some of which rises to the
surface because it is less dense than the surrounding material.
The upper mantle and the crust make up the lithosphere,
which is broken up into pieces called ‘plates’, which move
over the asthenosphere. The interaction of these plates is
responsible for earthquakes, volcanic eruptions and the
formation of
mountain ranges and ocean basins. The section on plate
tectonic theory later in this topic explains the
occurrence of these events further.
LAYERS OF MANTLE
Upper Mantle
The upper mantle extends from the crust to a depth of about
410 kilometers (255 miles). The upper
mantle is mostly solid, but its more malleable regions
contribute to tectonic activity.
Lithosphere
The lithosphere is the solid, outer part of the Earth, extending
to a depth of about 100 kilometers (62 miles). The lithosphere
includes both the crust and the brittle upper portion of the
mantle. The lithosphere is both the coolest and the most rigid
of Earth’s layers.
Asthenosphere
The asthenosphere is the denser, weaker layer beneath the
lithospheric mantle. It lies between about 100 kilometers (62
miles) and 410 kilometers (255 miles) beneath Earth’s surface.
The temperature and pressure of the asthenosphere are so
high that rocks soften and partly melt, becoming semi-molten
Transition Zone
From about 410 kilometers (255 miles) to 660 kilometers (410
miles) beneath Earth’s surface, rocks
undergo radical transformations. This is the mantle’s transition
zone. In the transition zone, rocks do not
melt or disintegrate. Instead, their crystalline structure
changes in important ways. Rocks become much, much
denser.
Lower Mantle
The lower mantle extends from about 660 kilometers (410
miles) to about 2,700 kilometers (1,678
miles) beneath Earth’s surface. The lower mantle is hotter and
denser than the upper mantle and transition zone. The lower
mantle is much less ductile than the upper mantle and
transition zone. Although heat usually corresponds to
softening rocks, intense pressure keeps the lower mantle solid.
CRUST
The Earth’s crust is the outermost layer, consisting mainly of
the chemical element’s silicon and
aluminium. The crust has two types: a continental crust that
varies in thickness between 20 km and 90
km, and an oceanic crust that varies in thickness between 5
km and 10 km. The oceanic crust is denser
than the continental crust.
Interior Structure of Earth
The Earth has a radius of about 6371 km, although it is about
22 km larger at equator than at poles. z
Density, (mass/volume), Temperature, and Pressure increase
with depth in the Earth. z The Earth has a
layered structure. This layering can be viewed in two different
ways:
(1) Layers of different chemical composition and
(2) Layers of differing physical properties.
Compositional Layering
Crust - variable thickness and composition
Continental - 10 - 70 km thick
Oceanic 8 - 10 km thick
Mantle - 3488 km thick, made up of a rock called peridotite.
Core - 2883 km radius, made up of Iron (Fe) with some Nickel
(Ni)
Layers of Differing Physical Properties
Lithosphere - about 100 km thick (up to 200 km thick beneath
continents), very brittle, easily fractures
at low temperature.
Asthenosphere - about 250 km thick - solid rock, but soft and
flows easily (ductile).
Mesosphere - about 2500 km thick, solid rock, but still capable
of flowing.
Outer Core - 2250 km thick, Fe and Ni, liquid
Inner core - 1230 km radius, Fe and Ni, solid
CONTINENTAL DRIFT
Today, most people know that landmasses on Earth move
around, but people have not always believed this. It was not
until the early 20th century that German scientist ALFRED
WEGENER put forth the idea that the Earth’s continents were
drifting. He called this movement Continental Drift. He was
not the first or only person to think this, but he was the first to
talk about the idea publicly. Wegener came up with this idea
because he noticed that the coasts of western Africa and
eastern South America looked like puzzle pieces, which might
have once fit together and then drifted apart. Looking at all
the continents he theorized that they had once been joined
together as a SUPERCONTINENT (which was later called
Pangaea) around 225 million years ago (see Figure). The
name Pangaea comes from the Ancient Greek words “pan,”
meaning entire, and “Gaia,” meaning Earth. Pangaea is not
the only supercontinent believed to have existed. Older
supercontinents are also believed to have come before
Pangaea.
The idea of moving landmasses seems obvious now, but
Wegener’s THEORY OF CONTINENTAL DRIFT (as he called it)
was not accepted for many years. Why? Well, for one thing,
Wegener did not have a convincing explanation for the
cause of the drifting (he suggested that the continents were
moving around due to the Earth’s rotation, which later turned
out to be wrong). Secondly, he was a meteorologist
(someone who studies weather), not a geologist, so
geologists didn’t think he knew what he was talking about.
FOSSIL EVIDENCE
One type of evidence that strongly supported the Theory of
Continental Drift is the fossil record. Fossils of similar types of
plants and animals in rocks of a similar age have been found
on the shores of different continents, suggesting that the
continents were once joined. For example, fossils of
Mesosaurus, a freshwater reptile, have been found both in
Brazil and western Africa. Also, fossils of the land reptile
Lystrosaurus have been found in rocks of the same age in
Africa, India and Antarctica.
PLATE TECTONICS
The Theory of Plate Tectonics builds on Wegener’s Theory of
Continental Drift. In the Theory of Plate Tectonics, it is tectonic
plates, rather than continents, which are moving. Tectonic
plates are pieces of the lithosphere and crust, which float on
the asthenosphere. There are currently seven plates that
make up most of the continents and the Pacific Ocean. They
are:
1. African Plate
2. Antarctic Plate
3. Eurasian Plate
4. Indo-Australian Plate
5. North American Plate
6. Pacific Plate
7. South American Plate
There are eight other smaller secondary plates as well as
many other microplates which do not make up significant
amounts of landmass. Tectonic plates not only move land
masses (continental crust), but also oceans (ocean crust).
Since the plates are floating on liquid rock, they are
constantly moving and bumping against each other. This
means that the sizes and positions of these plates change
over time.
Tectonic plates are able to move because the lithosphere,
which makes up the plates, has a higher strength and lower
density than the underlying asthenosphere. The solid plates
above move along on the liquid rock below. You may
imagine that these plates are zipping along, but in fact, they
are moving VERY SLOWLY! The speed of the plates ranges
from a typical 10–40 mm/year (about as fast as fingernails
grow) to as fast as 160 mm/year (about as fast as hair grows).
Geologists came to accept the Theory of Plate Tectonics in
the late 1950s and early 1960s after coming to understand
the concept of seafloor spreading. Seafloor spreading occurs
on the seafloor where oceanic plates are moving away from
each other (diverging). When this happens, cracks occur in
the lithosphere, which allows magma (hot liquid rock) to rise
and cool, forming a new seafloor. The opposite of
divergence is convergence. This occurs when plates are
moving towards each other. Material may push upwards
(obduction) forming mountains or downwards (subduction)
into the mantle. The material lost through subduction is
roughly balanced by the formation of new (oceanic) crust by
seafloor spreading.
Volcanic eruptions and earthquakes can occur, and
mountains and ocean trenches can be formed when
tectonic plates meet. Let’s look at some of these processes in
more detail.
MOUNTAINS AND VOLCANOES
What do mountains and volcanoes have in common? They
are both large, steep landforms made of rock that are
formed when tectonic plates are pushed and pulled.
Whether you get mountains or volcanoes depends on the
type of tectonic plates and where they are colliding. To
understand whether you will get mountains or volcanoes, you
need to remember two things.
1. There are two major types of tectonic plates: oceanic and
continental.
2. Oceanic plates are denser than continental plates.
Let’s look at how tectonic plates form mountains and
volcanoes.
1. When two oceanic plates diverge (pull apart), undersea
volcanoes are formed. Volcanoes are caused by cracks in
the Earth’s crust. An example of this is the Mid-Atlantic Ridge,
which extends from the Arctic Ocean to beyond the southern
tip of Africa. There are so many volcanoes in the Mid-Atlantic
Ridge, and they are so large, that it is considered the longest
mountain range in the world. Iceland is located on this ridge.
The red triangles on the picture show where there are active
volcanoes.
2. When two continental plates converge on land (collide
into each other), mountains are formed. This is because both
of the plates, which are similarly dense, will push up against
each other, causing the rock to get all folded and bunched
up. The crust in the region of a mountain is thicker than the
surrounding crust. The Himalayan Mountains are the result of
this type of process.
3. When an oceanic plate (1) converges with a continental
plate (2), the oceanic plate will move under the continental
plate (subduction) because it is denser (3). The oceanic plate
may go deep enough under the continental plate and into
the mantle that it melts and forms magma (4). Increased
pressure from beneath the Earth can build up and cause the
magma to seep up through weak spots in the crust (5).
Magma under high pressure sometimes comes through
volcanic vents in the form of flowing lava, forming a volcanic
cone (6).
WEATHERING
- The process that takes place as rocks and other parts of the
geosphere, are broken down into smaller
pieces.
- A process of decay, disintegration and decomposition of
rocks under the influence of certain physical
and chemical agencies.
*General term used when the surface of the earth is worn
away by the chemical as well as
mechanical actions of physical agents and the lower layers
are exposed.
*Involves two processes that often work together to
decompose or break down rocks
*It is a unique phenomenon happening on the Earth’s
surface.
TYPES OF WEATHERING
1. PHYSICAL/MECHANICAL WEATHERING
- Process of breaking big rocks into little ones.
*There is no change in the chemistry of the parent rock.
- Example: Breaking of a rock cliff into boulders and pebbles.
CAUSES OF PHYSICAL WEATHERING
A. Wind
- Sand and other rock particles that are carried by wind can
wear away exposed rock
surfaces.
B. Frost Action
- Water freezes in a crack of the rock surface, expanding and
splitting the rock.
*Water gets trapped in the rock
*Water freezes inside the cracks of the rocks
*Expands and makes the crack bigger.
C. Plants and Animals
- Plant roots force their way into cracks, animals uncover rock
and expose it to the
elements.
• ROOT PENETRATION
*Powerful plant roots grow into cracks and cause fractures.
*As the roots grow, they push the rock farther apart.
• SOIL BURROWING CREATURES
*Abrade small particles; they loosen and break apart rocks in
the soil.
D. Exfoliation
- Layers of rock peel off the main body of the rock
*Due to unloading or fluctuations in temperature, rocks
expand and crack.
*Release of pressure; pressure of rock is reduced.
2. CHEMICAL WEATHERING
- Involves changes that some substances can cause in the
surface of the rock that make it change
shape, or color.
*Takes place when at least some of the rock’s minerals are
changed in to different
substances.
- Process of chemical reactions between gases of the
atmosphere and surface of rocks.
CAUSES OF CHEMICAL ENGINEERING
A. Oxidation
- Occurs when oxygen from the air combines with iron-rich
minerals of the rock.
- Oxidation = rust
B. Carbonation
- Occurs when water combines with carbon dioxide in the air
to form carbonic acid.
*Carbonic acid easily dissolves rocks, limestone and marble.
*Can cause sink holes.
C. Hydrolysis
- Water combines with minerals such as mica and feldspar
found in granite, to form clay.
The rock weakens, and crumbles apart.
FACTORS AFFECTING THE RATE OF WEATHERING
1. Exposure
*Rate and type of weathering are dependent on exposure to
air, water and living things.
*The greater the amount of rock exposed, the greater the
weathering; direct relationship
2. Particle Size
*Increase in surface area increases the rate of weathering
3. Mineral Composition
*Rocks made of harder minerals weather slower than rocks
made of softer mineral.
4. Climate
*Physical and chemical weathering are affected by climate.
a. Cold and Moist Climates – Physical Weathering is
dominant.
b. Hot and Moist Climates – Chemical Weathering is
dominant.
c. Water – Major factor that causes weathering.
5. Time - *time goes on, more weathering occurs.
6. Humans - *excavation of land, mining, building, etc.
ENGINEERING IMPORTANCE OF ROCK WEATHERING
- As engineer is directly or indirectly interested in rock
weathering specially when he has to select a
suitable quarry for the extraction of stones for structural and
decorative purposes.
- The process of weathering always causes a loss in the
strength of the rocks or soil. For the construction
engineer it is always necessary to see that:
- To what extent the area under consideration for a proposed
project has been affected by
weathering and;
- What may be possible effects of weathering processes
typical of the area on the construction
Materials
Occurrence and Origin of Earthquake:
Prepared by: Jayson M. Arenal (BSCE-2A)
Terms:
Focus (Hypocenter): Focus is the point on the fault where
rupture occurs and the location from which seismic waves
are released.
Epicenter: Epicenter is the point on the earth’s surface that is
directly above the focus, the point where an earthquake or
underground explosion originates.
Fault Line: A Fault line is the surface trace of a fault, the line of
intersection between the earth’s surface.
Fault plane: Fault plane are the cracks or sudden slips of the
land.
Fault Scrap: A Fault scrap is the topographic expression of
faulting attributed to the displacement of the land surface by
movement along faults.
What is Earthquake/s?
-a sudden and violent shaking of the ground, sometimes
causing great destruction, as a result of movements within
the earth's crust or volcanic action.
Causes and Types of Earthquakes:
Plate Boundaries - scientific theory describing the large-scale
motion of the plates making up the Earth's lithosphere.
Lithosphere - rigid, rocky outer layer of the Earth, consisting of
the crust and the solid outermost layer of the upper mantle.
There are three main types of plate boundaries:
Convergent boundaries - where two plates are colliding.
Divergent boundaries – where two plates are moving apart.
Transform boundaries – where plates slide passed each other.
Tectonic Earthquakes - Earthquakes caused by plate
tectonics are called tectonic quakes. They account for most
earthquakes worldwide and usually occur at the boundaries
of tectonic plates.
Induced Earthquakes - are caused by human activity, like
tunnel construction, filling reservoirs and implementing
geothermal or fracking projects.
Fracking- process of drilling down into the earth before a
high-pressure water mixture is directed at the rock to release
the gas inside.
Mining – the process or industry of obtaining coal or other
minerals from a mine.
Water reservoir impoundment - reservoir with outlets
controlled by gates that release stored surface water as
needed in a dry season; may also store water for domestic or
industrial use or for flood control.
Large new reservoirs can trigger earthquakes. This is due to
either: change in stress because of the weight of water, or
more commonly by increased groundwater pore pressure
decreasing the effective strength of the rock under the
reservoir.
Volcanic quakes are associated with active volcanism. They
are generally not as powerful as tectonic quakes and often
occur relatively near the surface. Consequently, they are
usually only felt in the vicinity of the hypocenter.
Collapse quakes can be triggered by such phenomena as
cave-ins, mostly in karst areas or close to mining facilities, as a
result of subsidence.
Waves Produced due to earthquakes.
Seismic wave, vibration generated by an earthquake,
explosion, or similar energetic source and propagated within
the Earth or along its surface.
2 types:
Body waves-seismic wave that moves through the interior of
the earth.
P-waves, also known as primary waves or pressure waves,
travel at the greatest velocity through the Earth.
S-waves, also known as secondary waves, shear waves or
shaking waves, are transverse waves that travel slower than
P-waves.
2. Surface waves - waves that travel near the earth's surface.
Rayleigh waves, also called ground roll, travel as ripples
similar to those on the surface of water.
Love waves cause horizontal shearing of the ground. They
usually travel slightly faster than Rayleigh waves
Strength of Earthquakes: The intensity is a number (written as
a Roman numeral) describing the severity of an earthquake
in terms of its effects on the earth's surface and on humans
and their structures.
Mercalli Scale is based on observable earthquake damage.
Invented by Giuseppe Mercalli in 1902, this scale uses the
observations of the people who experienced the earthquake
to estimate its intensity. The Mercalli scale isn't considered as
scientific as the Richter scale, though.
Magnitude is the most common measure of an earthquake's
size. It is a measure of the size of the earthquake source and is
the same number no matter where you are or what the
shaking feels like.
The Richter scale – also called the Richter magnitude scale or
Richter's magnitude scale – is a measure of the strength of
earthquakes, developed by Charles F. Richter and presented
in his landmark 1935 paper, where he called it the
"magnitude scale".
Seismologists are Earth scientists, specialized in geophysics,
who study the genesis and the propagation of seismic waves
in geological materials.
Seismograph or seismometer, is an instrument used to detect
and record earthquakes.
Major Fault Lines in the Philippines:
There are five active fault lines in the country namely the
Western Philippine Fault, the Eastern Philippine Fault, the
South of Mindanao Fault, Central Philippine Fault and the
Marikina/Valley Fault System.
“The Big One “- a worst-case scenario of a 7.2-magnitude
earthquake from the West Valley Fault, a 100-kilometer fault
that runs through six cities in Metro Manila and nearby
provinces.
Earthquakes Prediction:
Earthquake prediction is usually defined as the specification
of the time, location, and magnitude of a future earthquake
within stated limits. But some evidence of upcoming
Earthquake are following:
- Unusual animal behavior
-Water level in wells
-Large scale of fluctuation of oil flow from oil wells
-Foreshocks or minor shocks before major earthquake
-Temperature change
-Uplifting of earth surface
-Change in seismic wave velocity
Effect of Earthquakes:
-Loss of life and property
-Damage to transport system e.g. roads, railways, highways,
airports, marine
-Damage to infrastructure.
-Chances of Floods
– Develop cracks in Dams
-Chances of fire short-circuit.
-Communications such as telephone wires are damaged.
-Water pipes, sewers are disrupted
-Economic activities like agriculture, industry, trade and
transport are severely affected.
Landslides- defined as the movement of a mass of rock,
debris, or earth down a slope
Shaking and ground rapture -disruptive up and down and
sideways motion experienced during an earthquake.
Fires- be started by broken gas lines and power lines, or
tipped over wood or coal stoves.
Soil liquefaction-occurs when a saturated or partially
saturated soil substantially loses strength and stiffness in
response to an applied stress such as shaking during an
earthquake
Tsunami -series of waves in a water body caused by the
displacement of a large volume of water, generally in an
ocean or a large lake.
Floods- a rising and overflowing of a body of water especially
onto normally dry land; also : a condition of overflowing.
Earthquake Safety Rules:
What Should I Do Before, During, And After An Earthquake?
What to Do Before an Earthquake
-Make sure you have a fire extinguisher, first aid kit, a batterypowered radio, a flashlight, and extra batteries at home.
-Learn first aid.
-Learn how to turn off the gas, water, and electricity.
-Make up a plan of where to meet your family after an
earthquake.
-Don't leave heavy objects on shelves (they'll fall during a
quake).
-Anchor heavy furniture, cupboards, and appliances to the
walls or floor.
-Learn the earthquake plan at your school or workplace.
What to Do During an Earthquake
-Stay calm! If you're indoors, stay inside. If you're outside, stay
outside.
-If you're indoors, stand against a wall near the center of the
building, stand in a doorway, or crawl under heavy furniture
(a desk or table). Stay away from windows and outside doors.
-If you're outdoors, stay in the open away from power lines or
anything that might fall. Stay away from buildings (stuff might
fall off the building or the building could fall on you).
-Don't use matches, candles, or any flame. Broken gas lines
and fire don't mix.
-If you're in a car, stop the car and stay inside the car until the
earthquake stops.
-Don't use elevators (they'll probably get stuck anyway).
-What to Do After an Earthquake
-Check yourself and others for injuries. Provide first aid for
anyone who needs it.
-Check water, gas, and electric lines for damage. If any are
damaged, shut off the valves. Check for the smell of gas. If
you smell it, open all the windows and doors, leave
immediately, and report it to the authorities (use someone
else's phone).
-Turn on the radio. Don't use the phone unless it's an
emergency.
-Stay out of damaged buildings.
-Be careful around broken glass and debris. Wear boots or
sturdy shoes to keep from cutting your feet.
-Be careful of chimneys (they may fall on you).
-Stay away from beaches. Tsunamis and seiches sometimes
hit after the ground has stopped shaking.
-Stay away from damaged areas.
-If you're at school or work, follow the emergency plan or the
instructions of the person in charge.
The Philippine Institute of Volcanology and Seismology
(PHIVOLCS) is a service institute of the Department of Science
and Technology (DOST) that is principally mandated to
mitigate disasters that may arise from volcanic eruptions,
earthquakes, tsunami and other related geotectonic
phenomena.
Why do scientist study Earthquakes?
-Scientists study earthquakes because they want to know
more about their causes and predict where they are likely to
happen.
-They also need to know how the ground moves during
earthquakes. This information helps scientists and engineers
build safer buildings – especially important buildings in an
emergency, like hospitals and government buildings.
--Earthquake engineers are working to make roads and
buildings safer in the event of a major earthquakes. This
includes both improving the design of new buildings and
bridges as well as strengthening older units to incorporate the
latest advances in seismic and structural engineering.
To properly test their buildings, engineers make sure that their
shake tables accurately represent the shaking of the Earth
during an earthquake. As a result, it is very important that
engineers understand the different seismic waves produced
during earthquakes and exactly how they cause the Earth to
move.
What is “Prospecting”?
•
It is the search for mineral deposits in a place,
especially by means of experimental drilling and
excavation. (Dictionary)
• Prospecting is the first stage of the geological analysis
of a territory. It is the search for minerals, fossils,
precious metals, or mineral specimens. (Geology)
Additional: Geological exploration follows a sequence of
multidisciplinary
activities: reconnaissance,
discovery, prospecting,
and
economic
mining.
The
exploration concept looks for a package of unique
stratigraphic age, promising favorable rocks, and type
structure to host certain groups of minerals.
Groundwater
• Groundwater is water that exists in the pore spaces
and fractures in rocks and sediments beneath the
Earth’s surface.
• It originates as rainfall or snow, and then moves
through the soil and rock into the groundwater
system, where it eventually makes its way back to the
surface streams, lakes, or oceans.
• Groundwater occurs everywhere beneath the
Earth’s surface, but is usually restricted to depth less
than about 750 meters.
Technical note:
Groundwater scientists typically restrict the use of the
term “groundwater” to underground water that can flow
freely into a well, tunnel, spring, etc. This definition excludes
underground water in the unsaturated zone. The unsaturated
zone is the area between the land surface and the top of the
groundwater system. The unsaturated zone is made up of
earth materials and open spaces that contain some moisture
but, for the most part, this zone is not saturated with water.
Groundwater is found beneath the unsaturated zone where
all the open spaces between sedimentary materials or in
fractured rocks is filled with water and the water has a
pressure greater than atmospheric pressure.
Additional: The water table is an underground boundary
between the soil surface and the area where groundwater
saturates spaces between sediments and cracks in
rock. Water pressure and atmospheric pressure are equal at
this boundary. ... Underneath the water table is the saturated
zone, where water fills all spaces between sediments.
Sources of Ground Water
Meteoric Water
• It is the water derived from precipitation (rain and
snow) although bulk of the rain water or melt water
from snow and ice reaches the sea through the
surface flows or runoffs a considerable part of
precipitation gradually infiltrates into ground water.
This infiltrated water continuous its downward journey
till it reaches the zone of saturation to become the
ground water in the aquifer.
• Almost entire water obtained from ground water
supplies belongs to this category.
Connate Water
• Groundwater encountered at great depths in
sedimentary rocks as a result of water having been
trapped in marine sediments at the time of their
deposition. These waters are normally saline. It is
accepted that connate water is derived mainly or
entirely from entrapped sea water as original sea
water has moved from its original place. Some
trapped water may be brackish.
Additional: Saline solution is a mixture of salt and water.
Saline has many uses in medicine. It's used to clean wounds,
clear sinuses, and treat dehydration.
Juvenile Water
• It is also called magmatic water and is of only
theoretical importance as far as water supply
scheme is concerned. It is the water found in the
cracks or crevices or porous of rocks due to
condensation of steam emanating from hot molten
masses or magmas existing below the surface of the
earth. Some hot springs and geysers are clearly
derived from juvenile water.
To understand the ways in which groundwater occurs, it is
needed to think about the ground and the water properties.
• Porosity,
• Saturated and unsaturated zones.
• Permeability
• Aquifer
• Storage coefficient
Porosity
• the property of a rock possessing pores or voids.
• is the quality of being porous, or full of tiny holes.
Liquids go right through things that have porosity
∅= VVVTx 100%
∅ = Porosity
V V = Void Volume
V T = Total Volume
• The first equation uses the total volume and
the volume of the void. Porosity = (Volume of Voids /
Total Volume) x 100%.
• The second equation uses the total volume and
the volume of the solid. Porosity = ( ( Total Volume Volume of the Solid ) / Total Volume ) x 100%.
Saturated and Unsaturated Zones
• Groundwater is found in two zones. The unsaturated
zone, immediately below the land surface, contains
water and air in the open spaces, or pores.
The saturated zone, a zone in which all the pores and
rock fractures are filled with water, underlies
the unsaturated zone
Permeability
• which is the ease with which water can flow through
the rock.
• Permeability defines how easily a fluid flows through
a
porous
material.
Materials
with
a
high permeability allow easy flow, while materials
with a low permeability resist flow.
Aquifer
• which is a geologic formation sufficiently porous to
store water and permeable enough to allow water
to flow through them in economic quantities.
• An aquifer is an underground layer of water-bearing
permeable rock, rock fractures or unconsolidated
materials (gravel, sand, or silt). Groundwater can be
extracted using a water well. The study of water flow
in aquifers and the characterization of aquifers is
called hydrogeology
How Aquifer works?
• When a water-bearing rock readily transmits water to
wells and springs, it is called an aquifer. Wells can be
drilled into the aquifers and water can be pumped
out. Precipitation eventually adds water (recharge)
into the porous rock of the aquifer.
Role of Confining Bed
Sometimes the porous rock layers become tilted in
the earth. There might be a confining layer of less porous rock
both above and below the porous layer. This is an example
of a confined aquifer. In this case, the rocks surrounding
the aquifer confines the pressure in the porous rock and its
water.
Three Types of Aquifers
• Unconfined Aquifer
• Confined Aquifer
• Leaky Aquifer
• Unconfined aquifers are those into which water seeps
from the ground surface directly above the aquifer.
• Confined aquifers are those in which an
impermeable dirt/rock layer exists that prevent water
from seeping into the aquifer from the ground
surface located directly above.
• A leaky aquifer, also known as a semiconfined aquifer, is an aquifer whose upper and
lower boundaries are aquitards, or one boundary is
an aquitard and the other is an aquiclude.
Aquitard
An aquitard is a partly permeable geologic formation. It
transmits water at such a slow rate that the yield is insufficient.
Pumping by wells is not possible. For example, sand lenses in a
clay formation will form an aquitard.
Aquiclude
An aquiclude is composed of rock or sediment that acts as a
barrier to groundwater flow. Aquicludes are made up of low
porosity and low permeability rock/sediment such as shale or
clay. Aquicludes have normally good storage capacity but
low transmitting capacity.
Aquifuge
An aquifuge is a geologic formation which doesn’t have
interconnected pores. It is neither porous nor permeable.
Thus, it can neither store water nor transmit it. Examples of
aquifuge are rocks like basalt, granite, etc. without fissures.
Additional: An aquitard is a zone within the Earth that restricts
the flow of groundwater from one aquifer to another. A
completely impermeable aquitard is called an aquiclude or
aquifuge. Aquitards comprise layers of either clay or nonporous rock with low hydraulic conductivity.
Storage coefficient or Storativity
• which is the volume of water that an aquifer releases
from or takes into storage per unit surface area of
aquifer per unit change in the component of area
normal to surface.
• capacity of an aquifer to release groundwater
Importance of Groundwater
• Groundwater, which is in aquifers below the surface
of the Earth, is one of the Nation's most important
natural resources. Groundwater is the source of
about 33 percent of the water that county and
city water departments supply to households and
businesses (public supply)
• Groundwater prospecting and extraction can both
be part of general water resource management
strategies to increase supply, or respond to climate
change induced water scarcity or variability.
• Groundwater, the great salvation of parched cities
and agricultural development, is the world's largest
freshwater resource. The volume of fresh water in all
the world's lakes, rivers and swamps adds up to less
than 1% of that of fresh groundwater
•
•
•
•
How it affects Civil Engineering?
• The presence of ground water beneath a foundation
can reduce the allowable bearing pressure of the
soil. The geotechnical report will take that into
consideration when they provide you with allowable
bearing pressures. It can also create problems with
the subgrade during construction- trucks or
equipment can cause it to “pump”.
Additional: The allowable bearing pressure is the maximum
load that the footing can support without failure with
appropriate factors of safety; AND. the maximum load that
the footing can support without intolerable settlements
(serviceability)
• During construction, if groundwater seeps into the
excavation, it will need to be removed. This can be
done by placing a pump in a sump at the low end of
the excavation to remove water as it accumulates,
or by placing pumps in wells around the excavation
to draw down the water table.
How do Civil Engineers Deal with Groundwater?
The first thing that needs to be done to ensure that
groundwater can be effectively dealt with is to gather
information to understand the problem. This involves a site
investigation, which might involve drilling and testing of
boreholes, measurement of groundwater levels and tests to
measure the permeability of the ground. Permeability is a
measure of how easily water flows through soils or rocks. High
permeability soils and rocks tend to be water-bearing and
are typical of the conditions where groundwater can cause
problems for construction projects.
The techniques used to control groundwater include:
Groundwater pumping (known as 'dewatering') – this
approach involves pumping groundwater from an array of
wells or sumps around the excavation. The objective is to
lower groundwater levels to below working level in the
excavation. Examples of this group of techniques include
sump pumping, well points, deep wells and ejector wells.
Low permeability cut-off walls – in this approach low
permeability barriers (known as 'cut-off walls') are installed
into the ground around the perimeter of the excavation.
These walls act as barriers to groundwater flow, and
effectively exclude groundwater from the excavation. The
requirement to pump groundwater is limited to pumping out
of the water trapped within the area enclosed by the cut-off
walls. Examples of the techniques used to form cut-off walls
include steel sheet-piling, concrete diaphragm walls,
concrete bored piles and bentonite slurry walls.
Grout barriers – this involves the injection into the ground of
fluid grouts that set or solidify in the soil pores and rock fissures.
The grout blocks the pathways for groundwater flow and can
produce a continuous zone of treated soil or rock around the
excavation that is of lower permeability than the native
material. This reduces groundwater inflow in a similar way to
cut-off walls. The most commonly used grouts are based on
suspensions of cement in water.
Artificial ground freezing – in this technique a very low
temperature refrigerant (either calcium chloride brine or
liquid nitrogen) is circulated through a series of closelyspaced boreholes drilled into the ground. The ground around
the boreholes is chilled and ultimately frozen. Frozen soil or
rock has a very low permeability, and will significantly reduce
groundwater inflow into any excavation.
Each of these approaches to groundwater control has
different advantages and disadvantages, and is applicable
only to certain soil or rock types. Selection of suitable
groundwater control measures is one of the key aspects of
the design of underground works.
THE WORK OF RIVERS
RIVER
A river is a natural flowing watercourse, usually freshwater,
from a high land towards an ocean, sea, lake or another
river. The route of a river is called a course of a river.
Anatomy of a River
HEADWATERS/SOURCE OF A RIVER
Place where a river begins its course/journey
Glacial headwaters (the source of water is snow
mountains)
Rain-fed Rivers (Starts from a particular area)
Springs (a place where water in the Earth, called
groundwater, flows to the surface naturally; forms when an
aquifer, or natural underground reservoir, fills with
groundwater and overflows)
Tributary or Affluent (a stream feeding a larger stream or a
lake)
TRIBUTARY
A tributary is a river that feeds into another river, rather than
ending in a lake, pond, or ocean.
CHANNEL
The shape of a river channel depends on how much water
has been flowing in it for how long, over what kinds of soil or
rock, and through what vegetation. The bends in a river
called “meanders” are caused by the water taking away soil
on the outside of a river bend and laying it down the inside of
a river bend over time.
RIVERBANK
The land next to the river is called the riverbank, and the
streamside trees and other vegetation is sometimes called
the “riparian zone.” This is an important, nutrient-rich area for
wildlife, replenished by the river when it floods.
MOUTH/DELTA
The end of a river is its mouth, or delta. At a river‟s delta, the
land flattens out and the water loses speed, spreading into a
fan shape. Usually this happens when the river meets an
ocean, lake, or wetland. As the river slows and spreads out, it
can no longer transport all of the sand and sediment it has
picked up along its journey from the headwaters. Because
these materials and nutrients help build fertile farmland,
deltas have been called “cradles” of human civilization.
Deltas are “cradles” for other animals as well, providing
breeding and nesting grounds for hundreds of species of fish
and birds.
UP, DOWN, LEFT, RIGHT
Downstream always points to the end of a river, or its
“mouth.” “Upstream” always points to the river‟s source, or
“headwaters.” As you look downstream, your right hand
corresponds to “River Right.” Your left hand corresponds to
“River Left.”
Three Functions of Rivers
A. EROSION
Erosional work of rivers carves and shapes the landscape
through which they flow. The energy in a river causes erosion.
The bed and banks can be eroded making it wider, deeper
and longer.
Headward erosion makes a river longer. This erosion
happens near its source. Surface run-off and through flow
causes erosion at the point where the water enters the valley
head.
Vertical erosion makes a river channel deeper. This
happens more in the upper stages of a river (the V of vertical
erosion should help you remember the v-shaped valleys that
are created in the upper stages).
Lateral erosion makes a river wider. This occurs mostly in the
middle and lower stages of a river.
C. DEPOSITION
The process of eroded material being dropped.
When a river loses energy, it will drop or deposit some of the
material it is carrying.
Deposition may take place when a river enters an area of
shallow water or when the volume of water decreases - for
example, after a flood or during times of drought.
Deposition is common towards the end of a river's journey,
at the mouth.
Deposition at the mouth of a river can form deltas.
RIVER‟S DROPPING OF LOADS
1. WHEN VOLUME DECREASES
DRY SEASON
DRY REGION WITH HIGH EVAPORATION
PRESENSE OF PERMEABLE ROCKS
RECEDING FLOOD WATERS
2. WHEN SPEED DECREASES
RIVER MAY ERODE IN 4 WAYS
IT ENTERS A LAKE
1. ABBRASION/CORRASION
IT ENTERS A CALM SEA
The process of sediments wearing down the bedrock and the
banks.
IT ENTERS A GENTLY SLOPING PLAIN
2. ATTRITION
The collision between sediment particles that break into
smaller and more rounded pebbles
3. HYDRAULIC ACTION
The force of water against the banks compressing air pockets
into cracks, which expand and fracture the rock over time
4. SOLUTION/CORROSION
The process of acidic water dissolving soluble sediment
B. TRANSPORTATION
Transportation of material in a river begins when friction is
overcome. Material that has been loosened by erosion may
be then transported along the river.
RIVER TRANSPORTATION IN 4 WAYS
1. TRACTION - Large boulders and rocks are rolled along the
river bed
2. SALTATION - Small pebbles and stones are bounced along
the river bed
3. SUSPENSION - Fine light material is carried along in the
water
4. SOLUTION - Minerals are dissolved in the water and carried
along in solution
THE WORKS OF RIVERS
POTHOLES
These are various shaped depressions of different dimensions
that are developed in the river bed by excessive localized
erosion by the streams. The pot holes are generally cylindrical
or bowl shaped in outline these are commonly formed in the
softer rocks occurring at critical location in the bedrock of a
stream. The formation process for a pothole may be initiated
by a simple plucking out of a protruding or outstanding rock
projection at the river bed by hydraulic action.
GEORGES AND CANYONS
Georges are very deep and narrow valley with very steep
and high walls on either side. A canyon is a specific type of
George where the layers cut down by a river are essentially
stratified and horizontal in attitude.
RIVER MEANDERING
When a stream flows along a curved, zigzag path acquiring a
loop-shaped course, it is said to mender. Menders are
developed mostly in the middle and lower reaches of major
stream where lateral erosion and depositions along opposite
banks become almost concurrent geological activities of the
stream, when a stream is flowing through such a channel it
cannot be assumed to have absolutely uniform velocities all
across its width. Thus the same river is eroding its channel on
the concave side and making its progress further inland
whereas on the convex side it is depositing. A loop shaped
outline for the channel is a natural outcome where a stream
seen from a distance.
OXBOW LAKES
In the advanced stages of a meandering stream only
relatively narrow strips of land separate the individual loops
from each other. During high-water times, as during small
floods, when the stream acquires good volume of water, it
has a tendency to flow straight, some of the intervening strips
of land between the loops get eroded. The stream starts
flowing straight in those limited stretches, thereby leaving the
loops or loops on the sides either completely detached or
only slightly connected. This isolated curved or looped
shaped area of the river, which often contains some water
are called oxbow lakes.
THE WORK OF WIND
WIND
Air in motion is called Wind. Wind is one of the three major
agents of change on the surface of the earth, other two
being river and glaciers. Wind act as agent of erosion, as a
carrier for transporting particles and grains so eroded from
one place and also for depositing huge quantities of such
wind-blown material at different places.
Three Functions of Wind
A. WIND EROSION
THREE DIFFERENT METHODS OF WIND EROSION
1. DEFLATION
Wind possess not much erosive power over rocks the ground
covered with vegetation. But when moving with sufficient
velocity over dry and loose sand it can remove or swept
away huge quantity of the loose material from the surface.
This process of removal of particle of dust and sand by strong
wind is called deflation.
2. ABRASION
Wind becomes a powerful agent for rubbing and abrading
the rock surface when naturally loaded with sand and dust
particles. This type of erosion involving rubbing, grinding,
polishing the rock surface by any natural agent is termed as
abrasion.
3. ATTRITION
The sand particles and other particles lifted by the wind from
different places are carried away to considerable distances.
The wear and tear of load particles suffered by them due to
mutual impacts during the transportation process is termed as
attrition.
B. SEDIMENTATION TRANSPORT OF WIND
Sources of sediments: Wind is an active agent of sediment
transport in nature. Materials of fine particle size such as Clay,
silt and sand occurring on surface of the earth are
transported in huge volumes from one place to another in
different regions of the world.
METHOD OF TRANSPORT:
1. SURFACE CREEP
In a wind erosion event, large particles ranging from 0.5 mm
to 2 mm in diameter are rolled across the soil surface. This
causes them to collide with, and dislodge, other particles.
Surface creep wind erosion results in these larger particles
moving only a few meters.
2. SUSPENSION
The light density clay and silt particles may be lifted by the
wind from the ground and are carried high up to the upper
layer of the wind where they move along with the wind. This is
called transport in suspension.
3. SILTATION
The heavier and coarse sediments such as sand grains,
pebbles and gravels are lifted up periodically during high
velocity wind only for short distance. They may be dropped
and picked up again and again during the transport process
saltation is therefore, a process of sediment transport in a
series of jumps. The transport power of wind: The transporting
power of wind depends on its velocity as also on the size,
shape and density of the particles. The amount of load
already present in the wind at a given point of time also
determines its capacity to take up further load.
C. DEPOSITION BY WIND AEOLIAN DEPOSITS
Sediments and particles once picked up by the wind from
any source on the surface are carried forward for varying
distances depending on the carrying capacity of the wind.
Wherever and whenever the velocity of wind suffers a check
from one reason or another a part or whole of the wind load
is deposited at that place. These wind made deposits may
ultimately take the shape of landform that are commonly
referred as aeoline deposits.
TWO MAIN TYPES OF DEPOSIT
1. DUNES
These are variously shaped deposits of sand-grade particles
accumulated by wind. A typical sand dune is defined as
broad conical heap. A dune is normally developed when a
sand laden wind comes across some obstruction. The
obstruction causes some check in the velocity of the wind ,
which is compelled to drop some load over, against or along
the obstruction when the process is continued for a long time,
the accumulated sand takes the shape of mound or a ridge.
A typical dune is characterized with a gentle windward side
and a steep leeward slope.
2. LOESS
Used for wind-blown deposits of silt and clay grade particles.
Typically Loess is unconsolidated, unratified and porous
accumulation of particles. Strong winds blowing over very
extensive area of deserts, outwash plains and soil loosened
by plough pick up vast amount of fine grade particles for
transportation in suspension, when such dust laden winds
passing over steppes and other flat surfaces are intercepted
by precipitation they drop their entire loads on the surface
below. This process is repeated for years. Accumulations of
such sediments over years have resulted in the present loess
deposits.
THE WORKS OF WIND
1. NEEDLES
Complete to erosion of soft rocks by high speed winds allows
steep gradient rocks stand uneroded and still. They look like
needles and therefore known as rocky Needles.
2. MUSHROOM OR PEDESTAL ROCKS
Wind erosion takes place at the average height of 1 meter
from the Earth‟s surface. While above height of average 2
meters, erosional process is again very low. Resultantly middle
portion of vertical rocks is eroded by high speed winds and
after erosion rocks look like mushrooms.
3. ZEUGEN
„Zeugen‟ is a word from German language which means
„Like Table‟. When soft rocks covered by hard rocks are
eroded by winds, hard rocks left behind looks like table and
known as „Zeugen‟. Their length may vary from 1 meter to 30
meters. Along with winds, rainfall and weathering also help in
formation of „Zeugen‟.
4. WINDOW AND BRIDGE
Continuous erosion by high velocity winds forms holes in the
rocks. Such holes are called Wind Windows. Further, the
combined action of deflation and abrasion makes the wind
windows larger and wider which assumes an arch like shape
with solid roof over them. Such land forms are called Wind
Bridges.
It is the solvent action of seawater which is particularly strong
in environment where the shore is of vulnerable chemical
composition.
B. MARINE DEPOSITION
Seas are regarded as most important and extensive
sedimentation basins, this becomes evident from the fact
that marine deposits of practically of all the geological ages.
CLASSIFICATION OF DEPOSITS
1. SHALLOW WATER DEPOSITS (NERITIC DEPOSITS)
These include marine deposits laid down in neritic zone of the
sea, which extends from the lowest tide limit to the place of
the continent shelf where the slope becomes steeper.
EX. BEACHES, SPLITS AND BARS; TAMBOLO
2. DEEP WATER DEPOSITS
These deposits consists mostly of Mud and oozes and are
called as pelagic deposits. The oozes that form bulk of some
such deposits consist of small organisms known collectively as
planktons. Death and decay of these organisms and plants
followed by their accumulation in regular and irregular
shapes These deposits are commonly called as reefs.
EX. CORAL REEFS
THE WORKS OF OCEAN/SEA
THE WORK OF SEA
1. SEA CLIFFS
The work of sea water is performed by several marine agents
like sea waves, oceanic currents, tidal waves and tsunamis
but the sea waves are most powerful and effective erosive
agent of coastal areas.
A Sea cliff is seaward facing steep front of a moderately high
shoreline and indicates the first stage of the work of waves on
the shore rocks. There may be a number of sea cliffs seen on
a shore line. They are outstanding rock projection having
smoothened seaward sloping surface.
All the geological work performed by marine water is due to
regular and irregular disturbances taking places in the body
of water. Mostly in the surface layer and distinguished as
waves and currents.
2. WAVE-CUT TERRACES
THREE WAYS OF MARINE EROSION
A wave-Cut Terrace is a shallow shelf type structure, carved
out from the shore rocks by the advancing sea waves. The
waves first of all cut a notch where they strike against the cliff
rock again and again. The notch is gradually extended
backward to such a depth below the overlying rock that the
latter becomes unsupported from below. The cliff eventually
falls down along the notch. A platform or bench is thus
created over which the seawater may rush temporarily and
periodically. The resulting structure is called a wave curt
terrace.
1. HYDRAULIC ACTION
3. SPITS AND BARS
This is the process of erosion by water involving breaking,
loosening and plucking out of loose, disjointed blocks of rocks
from their original places by the strong forces created by the
impact of sea waves and currents.
These are ridge shaped deposits of sand and shingle that
often extends across the embayment.
2. MARINE ABRASION
It is the form of marine deposit that connects a headland
and an island or one island with another island.
Works of Ocean/Sea
A. MARINE EROSION
Marine water erodes the rocks at the shore and elsewhere
with which it comes in contact in a manner broadly similar to
that of stream water.
This involves the rubbing and grinding action of seawater on
the rocks of the shore with the help of sand particles and
other small fragments that are hurdled up again these rocks.
3. CORROSION
4. TOMBOLA
SYMMETRY ELEMENTS OF CRYSTALLOGRAPHGIC SYSTEM
MINERALOGY VS CRYSTALLOGRAPHY
Mineralogy - is the science of minerals, which
includes their crystallography, chemical composition,
physical properties, genesis, their identification and their
classification
Crystallography - is the study of crystals and the
crystalline state. It is the
key in understanding the structures of crystalline materials
It is imperative to learn the key concepts of
Crystallography in order to further understand and answer
the question ‘how’ and ‘why’ do Minerals form?
MINERALS VS CRYSTALS
Crystals - A Crystal is a solid body bounded by
natural planar surfaces generally called crystal faces that are
the external expression of a regular internal arrangement of
constituent atoms or ions. Crystals are known as anisotropic
substances. Meaning, the physical properties exhibit
variations along different directions.
Minerals - Minerals are naturally occurring inorganic
elements or compounds having an orderly internal structure
and characteristic chemical composition, crystal form, and
physical properties. Although it is contestable that there are
some organic substances that are considered minerals, like
seashells, but generally, what we are looking for are inorganic
substances.
All in all, minerals and crystals shares lots of similarities.
One of these is its most important property, the structured
internal arrangement of atoms. The physical properties of
minerals mainly depends on its chemical composition as well
as the organized pattern found inside the crystals.
Key Differences between Crystals and Minerals
Crystals are artificially or naturally made whereas
Minerals only form naturally. Crystals can either be organic or
inorganic while Minerals are mostly inorganic. Therefore,
Minerals are all Crystals but not all Crystals are minerals.
WHEN DO MINERALS FORM?
•
•
•
Their constituent atoms and ions are free to
come together in the correct proportions.
The existing conditions are such that growth
will take place at a reasonably slow and
steady state.
The external surface of the growing crystal is
not constrained physically.
HOW DO NATURAL CRYSTALS FORM?
Crystallization – also known as solidification is the process of
crystal formation via mechanisms of crystal growth.
Minerals form in various conditions at different rates:
•
•
High temperatures and pressures (Earth’s Core)
Evaporation of Liquid Solutions
The formation of crystals is only possible if correct proportions
of atoms required to make the minerals or crystals are
present. For an example, iron and sulfur is abundant in a
certain area, it is highly probable for Iron Sulfide (FeS 2) or
Pyrite to be produced when both elements are subjected to
high pressure and heat. We must also consider the fact that it
needs a long period of time in order to consolidate all the
materials eventually turning into minerals. If there such cases
wherein the external surfaces of the crystals are physically
constrained, the growth of mineral will be hindered as well.
However, if only one or two external faces of the crystals are
only subjected to resistance, the other faces will continue
grow larger until it ceases to grow anymore.
BASIC TERMS USED IN CRYSTALLOGRAPHY
Crystal Structure - is the orderly arrangement of atoms or
group of atoms (within a crystalline substance) that constitute
a crystal.
Morphological Crystals - are finite crystallographic bodies
with finite faces that are parallel to lattice planes.
Lattice - is an imaginary three-dimensional framework that
can be referenced to a network of regularly spaced points,
each of which represents the position of a motif.
Unit Cell - This is a pattern that yields the entire pattern when
translated repeatedly without rotation in space.
Motif - This is the smallest representative unit of a structure. It is
an atom or group of atoms that, when repeated by
translation, give rise to an infinite number of identical
regularly organized units.
Crystal Structure, as the definition suggests, is the
arrangement of atoms or group of atoms composing the
crystals. The shape created in accordance with the internal
arrangement of the atoms, and faces relative to lattice
planes are under what we call Crystal Morphology, thus the
term Morphological Crystals.
It must be iterated that Crystal Structure is not the same as
Lattice and Motif. It should be given emphasis that the Crystal
Structure is made up of Lattice and Motif. Lattice being an
imaginary three-dimensional framework represents the
translational properties of the crystal structure in which the
motif are located thus, Lattice is also the representation of
the Motif. Motif in some other term is called the base and can
be consisted of atoms, molecules, or ions depending on the
chemical composition of the concerned mineral.
Within the lattice, the lattice points are shown. These lattice
points are the exact location of the motif. The distance
between the lattice points are what we call the lattice
parameters or lattice constants, it is the difference in length
and angular displacement between two lattice points. With
the given conjecture, it is safe to conclude that each lattice
point have identical surroundings. Furthermore, these lattice
points define the corner of the unit cell which is the building
blocks of a crystal structure. The principle of translation
applies to every unit cell in every direction. By repeating the
unit cells in several direction, one must create the crystal
structure.
BASIC
CRYSTAL STRUCTURE
CRYSTAL SHAPE
Key Features of Crystal Boundaries
a.
the angles between them are determined only by
the internal crystal structure.
b.
the relative sizes of the crystal boundaries depend on
the rate of growth of the crystal boundaries.
Factors in Variation of Crystal Boundaries
A combination of Lattice and
the Crystal structure:
Motif creates
a.
absorption of impurity atoms that may hinder growth
on some boundary faces
b.
Atomic bonding that may change with temperature
etc.
A set of of 2d Crystal Structures parallel with each other
create a 3d Crystal Lattice and Structure in which each unit
cells and the position of each particles are defined.
Law of Constancy of Angles by Steno, 1669
Quartz (SiO2 )
““The angles between corresponding faces on
different crystals of a substance are constant””
CLASSIFICATION OF CRYSTALS
The figure shown is a typical shape of a Quartz. It has
chemical properties of SiO4 -tetrahedra. However, the quartz
does not look like tetrahedron just like as shown above.
Remember that a unit cell is the building block of the crystal,
when we create a bigger piece of atomic arrangement, it still
doesn’t look like the quartz in the picture above until we see
the whole structure consisting a stack of SiO 4 -tetrahedra
forming the quartz we’ve seen in the picture.
Crystals are classified based on the fundamental
property of patterns, which is repetition. It was discussed that
a collection of unit cells form a lattice, and together with
motif, it creates a crystal structure or crystal lattice that are
then repeated together at a certain direction through
translation and other symmetry operation to form a distinct
and unique minerals.
3 Categories of Symmetry Operations
•
translation (parallel periodic displacement)
• point group symmetry (rotations, rotation inversion axes,
reflection planes)
• space-group symmetry (screw axes, glide planes).
Note: Directions may or may not be perpendicular to
each other. Hexagonal Crystal System has 4 axes while nonHexagonal has 3 axes.
Bravais Lattices
Bravais Lattice - is as an infinite set of discrete points with an
arrangement and orientation that appears exactly the same
from whichever of the points the array is viewed
Symmetry Elements
It was demonstrated by Auguste Bravais in 1850 that only
these 14 types of unit cells are compatible with the orderly
arrangements of atoms found in crystals.
Symmetry is the most important of all properties in the
identification of crystalline substances.
Crystal Systems
Plane of Symmetry - plane along which the crystal may be
cut into exactly similar halves each of which is a mirror image
of the other.
•
32 Combinations of Crystal Systems by PointSymmetry
•
6 Classifications of Crystal by Crystallographic Axes
and Point-Symmetry
•
14 Classifications of Crystal by Bravais Lattices
In case of a Cube, there are 9 ways to cut a cube resulting to
Unit Cell Particles
identical pairs.
Axis of Symmetry - is a line about which the crystal may be
rotated so as to show the same view of the crystal more than
once per revolution
Unit Cell Structure
Center of Symmetry - is the point from which all similar faces
are equidistant. It is a point inside the crystal such that when
a line passes through it, you’ll have similar parts of the crystal
on either side at same distances.
CLASSIFICATION OF CRYSTALS BASED ON CRYSTALLOGRAPHIC
AXES
As shown in the figure, there is a center of symmetry in a
cube while a tetrahedron does not have one. It only means
that not all crystal structures have the center of symmetry.
Cell Constants Angles
CUBIC
a=b=c
α=γ=β=90°
Crystallographic Axes
Crystallographic Axis- is an imaginary line that
defines the coordinate system within a crystal. It is a line
perpendicular to the faces of the crystals.
Cell Constants Angles
a=b
α=γ=β=90°
TETRAGONAL
ORTHOROMBIC
Cell Constants Angles
none
HEXAGONAL
α=γ=β=90°
HEXAGONAL
Cell Constants Angles
a=b
MONOCLINIC
α=B=90°; γ=120°
MONOCLINIC
Cell Constants Angles
None
α=γ=90°
TRICLINIC
TRICILINIC
Edge Lengths Angles
None
RHOMBOHEDRAL
none
CLASSIFICATION OF CRYSTALS BASED ON BRAVAIS LATTICE
CUBIC
PHYSICAL PROPERTIES OF MINERALS
TETRAGONAL
ORTHOROMBIC
Isotropic minerals are minerals with properties in any
directions. The travel of light is the same in any direction as
well as the velocity. Substances such as gases, liquids, glasses,
and minerals with crystallize is isotropic. The opposite of is
anisotropic minerals wherein the travel of light is different in
every direction as well as its velocity. Polymorphism minerals
"many forms" chemical composition can exist with two or
more different crystal structures. Cohesion is the force
between molecules of minerals it is the same with elasticity
but the difference is elasticity is responsible for molecules to
go back to its original position after expose to foreign force
the result was cleavage the tendency ng mineral to break
along smooth or weak planes parallel to zones, parting ability
ng mineral crystals or crystalline to split, fracture or it has
irregular surface. Hardness or ability of mineral crystals or
crystalline to split into pieces. Tendency resistance to break or
bend. Specific Gravity – also known as relative density, is a
unitless number that expresses the ratio between the weight.
density of minerals is the ratio of mass to volume. Diaphaneity
ability of minerals to transmit ng light. Minerals have different
colors depending on its chemical composition and such, for
color streak is the one defines its true color. Luster classify was
based if it is metallic or not. Magnetism is as simple as if it
reacts to magnetic field.
Quartz
- Quartz is a chemical compound consisting of one part
silicon and two parts oxygen. It is silicon dioxide (SiO2).
- It is the most abundant mineral found at Earth's surface, and
its unique properties make it one of the most useful natural
substances.
- It is abundant in igneous, metamorphic, and sedimentary
rocks.
Amethyst quartz: Purple crystalline quartz is known as
"amethyst." When transparent and of high quality, it is often
cut as a gemstone. This specimen is about four inches (ten
centimeters) across and is from Guanajuato, Mexico.
-It is highly resistant to both mechanical and chemical
weathering.
-This durability makes it the dominant mineral of mountaintops
and the primary constituent of beach, river, and desert sand.
Chemical
Classification
Color
Streak
Luster
Diaphaneity
Cleavage
Mohs Hardness
Specific Gravity
Diagnostic
Properties
Chemical
Composition
Crystal System
Uses
Physical Properties of Quartz
Silicate
Quartz occurs in virtually every color.
Common colors are clear, white, gray,
purple, yellow, brown, black, pink, green,
red.
Colorless (harder than the streak plate)
Vitreous
Transparent to translucent
None - typically breaks with a conchoidal
fracture
7
2.6 to 2.7
Conchoidal fracture, glassy luster, hardness
SiO2
Hexagonal
Glass making, abrasive, foundry sand,
hydraulic fracturing proppant, gemstones
Flint: Flint is a variety of microcrystalline or cryptocrystalline
quartz. It occurs as nodules and concretionary masses and
less frequently as a layered deposit. It breaks consistently with
a conchoidal fracture and was one of the first materials used
to make tools by early people.
Quartz glass sand: High-purity quartz sandstone suitable for
the manufacture of high-quality glass. "Glass sand" is a
sandstone that is composed almost entirely of quartz grains.
Blue Aventurine Quartz: Aventurine is a colorful variety of
quartz that contains abundant shiny inclusions of minerals
such as mica or hematite.
Rock crystal quartz: Transparent "rock crystal" quartz. This
specimen shows the conchoidal fracture (fracture that
produces curved surfaces) that is characteristic of the
mineral. Specimen is about four inches (ten centimeters)
across and is from Minas Gerais, Brazil.
Chert: Chert is a microcrystalline or cryptocrystalline quartz. It
occurs as nodules and concretionary masses and less
frequently as a layered deposit.
Uses
Crushed and powdered feldspar are
important raw materials for the manufacture
of plate glass, container glass, ceramic
products, paints, plastics and many other
products. Varieties of orthoclase, labradorite,
oligoclase, microcline and other feldspar
minerals have been cut and used as
faceted and cabochon gems.
Silicified wood: Silicified "petrified" wood is formed when
buried plant debris is infiltrated with mineral-bearing waters
which precipitate quartz.
USES of Quartz
1 Glass Making
2 Abrasive
3 Foundry Sand
4. Petroleum Industry
Feldspar
-"Feldspar" is the name of a large group of rock-forming
silicate minerals that make up over 50% of Earth's crust.
-They are found in igneous, metamorphic, and sedimentary
rocks in all parts of the world.
-Feldspar minerals have very similar structures, chemical
compositions, and physical properties.
-Common feldspars include orthoclase (KAlSi3O8), albite
(NaAlSi3O8), and anorthite (CaAl2Si2O8).
-Feldspar minerals have many uses in industry.
- They are used to manufacture a wide variety of glass and
ceramic products.
-They are also widely used as fillers in paints, plastics and
rubber.
-Several popular gemstones are feldspar minerals. These
include moonstone, sunstone, labradorite, amazonite and
spectrolite.
Chemical
Classification
Color
Streak
Luster
Diaphaneity
Cleavage
Mohs
Hardness
Specific
Gravity
Diagnostic
Properties
Chemical
Composition
Crystal
System
Physical Properties of Feldspar
Silicate
Usually white, pink, gray or brown. Also
colorless, yellow, orange, red, black, blue,
green.
White
Vitreous. Pearly on some cleavage faces.
Usually translucent to opaque. Rarely
transparent.
Perfect in two directions. Cleavage planes
usually intersect at or close to a 90 degree
angle.
6 to 6.5
2.5 to 2.8
Perfect cleavage, with cleavage faces
usually intersecting at or close to 90 degrees.
Consistent hardness, specific gravity and
pearly luster on cleavage faces.
A generalized chemical composition of
X(Al,Si)4O8, where X is usually potassium,
sodium, or calcium, but rarely can be
barium, rubidium, or strontium.
Triclinic, monoclinic
Feldspar from the Moon: The "Genesis Rock" is one of the most
famous rocks ever collected. Apollo 15 astronauts James
Irwin and David Scott collected it from the Moon in 1971.
Analysis revealed that it is made up almost entirely of
anorthite, a plagioclase feldspar, and is approximately 4
billion years old.
Feldspar in a Martian meteorite NWA 7034 is made of
cemented fragments of basalt, a rock that forms from rapidly
cooled lava. The fragments within the meteorite are mostly
feldspar and pyroxene.
USES OF FELDSPAR IN CIVIL ENGINEERING
Feldspars are used as fluxing agents to form a glassy
phase at low temperatures and as a source of alkalies and
alumina in glazes. They improve the strength, toughness, and
durability of the ceramic body, and cement the crystalline
phase of other ingredients, softening, melting and wetting
other batch constituents.
Augite
• A common rock-forming mineral of dark-colored
igneous rocks.
• Note: Igneous rocks are formed from the solidification
of
molten rock material.
•
Augite is a rock-forming mineral that commonly
occurs in mafic and intermediate igneous rocks such
as basalt, gabbro, andesite, and diorite.
• Note: A mafic mineral or rock is a silicate mineral or
igneous rock rich in magnesium and iron.
Common Rock-forming Mineral
• A mineral must:
• A) be one of the most abundant minerals in Earth’s
crust;
• B) be one of the original minerals present at the time
of a crustal rock’s formation; and,
•
C) be an important mineral in determining a rock’s
classification.
•
Note: Minerals that easily meet these criteria include:
plagioclase
feldspars,
alkali
feldspars, quartz, pyroxenes,
amphiboles,
micas,
clays, olivine, calcite and dolomite
•
It is found in these rocks throughout the world,
wherever they occur.
•
Augite is also found in ultramafic rocks and in
some metamorphic rocks that form under high
temperatures.
•
Note: ULTRAMAFIC ROCKS-An igneous rock with a
very low silica content and rich in minerals such as
hypersthene, augite, and olivine. These rocks are also
known as ultrabasic rocks.
Examples
lamprophyre,
include: peridotite,
kimberlite,
lamproite, dunite, and komatiite.
•
Augite
has
a
chemical
composition
of
(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6 with many paths of solid
solution.
•
Commonly
associated minerals include orthoclase, plagioclase,
olivine, and hornblende.
•
•
•
Luster
Diaphaneity
Augite
•
Streak
Augite is the most common pyroxene mineral and a
member of the clinopyroxene group.
Pyroxenes are a group of dark-colored rock-forming
minerals found in igneous and metamorphic rocks
throughout the world. They form under conditions of
high temperature and/or high pressure.
Note: Some people use the names "augite" and
"pyroxene" interchangeably, but this usage is strongly
discouraged.
•
There are a large number of pyroxene minerals,
many of which are distinctly different and easy to
identify.
•
Augite, diopside, jadeite, spodumene,
and
hypersthene are just a few of the distinctly different
pyroxene minerals.
•
Clinopyroxene- a member of the pyroxene group of
minerals having a monoclinic crystal structure, such
as augite, diopside, or jadeite
Physical Properties of Augite
Chemical
A single chain inosilicate
Classification
Color
Dark green, black, brown
Cleavage
Mohs Scale
Specific
Gravity
Diagnostic
Properties
Chemical
Composition
Crystal
System
Uses
White to gray to very pale green. Augite is
often brittle, breaking into splintery
fragments on the streak plate. These can be
observed with a hand lens. Rubbing the
debris with a finger produces a gritty feel
with a fine white powder beneath.
Vitreous on cleavage and crystal faces. Dull
on other surfaces.
Usually translucent to opaque. Rarely
transparent.
Prismatic in two directions that intersect at
slightly less than 90 degrees
5.5 to 6
3.2 to 3.6
Two cleavage directions intersecting at
slightly less than 90 degrees. Green to black
color. Specific gravity.
A complex silicate.
(Ca,Na)(Mg,Fe,Al)(Si,Al)2 O6
Monoclinic
No significant commercial use.
Hornblende
•
Hornblende is a field and classroom name used for a
group of dark-colored amphibole minerals found in
many types of igneous and metamorphic rocks.
•
These minerals vary in chemical composition but are
all double-chain inosilicates with very similar physical
properties.
•
A generalized composition for the hornblende group
is shown below.
•
(Ca,Na)2-3 (Mg,Fe,Al)5 (Si,Al)8 O22 (OH,F)2
•
Note that calcium, sodium, magnesium, iron,
aluminum, silicon, fluorine and hydroxyl can all vary in
abundance. This creates a huge number of
compositional variants. Chromium, titanium, nickel,
manganese, and potassium can also be part of the
complex composition and further indicates the
generalization of the formula given above.
Hornblende Minerals
•
A small list of the hornblende minerals is given below
with their chemical compositions.
Mineral
Chemical Composition
Edenite
Ca2 NaMg5 (AlSi7 )O22(OH)2
Ferro-actinolite
Ca2 (Fe,Mg5 )(Si8 O22 (OH)2
Ferro-edenite
Ca2 NaFe5 (AlSi7 )O22 (OH)2
Ferro-pargasite
Ca2 NaFe4 Al(Al2 Si6 )O22 (OH)2
Ferro-tschermakite
Ca2 Fe3 Al2 (Al2 Si6)O22 (OH)2
Glaucophane
Na2 Mg3 Al2 Si8 O22 (OH)2
Kaersutite
Ca2 Na(Fe,Mg)4Ti(Al2 Si6 O22 (OH)2
•
Pargasite
Ca2 NaMg4 Al(Al2 Si6 )O22 (OH)2
•
Tremolite
Ca2 (Mg,Fe5 )(Si8 O22 (OH)2
Tschermakite
Ca2 Mg3 Al2 (Al2 Si6)O22 (OH)2
•
As noted above, hornblende is a name used for a
number of dark-colored amphibole minerals that are
compositional variants with similar physical
properties. These minerals cannot be distinguished
from one another without laboratory analysis.
Hornblende as a Rock-Forming Mineral
• Hornblende is a rock-forming mineral that is an
important constituent in acidic and intermediate
igneous
rocks
such
as granite, diorite,
syenite, andesite, and rhyolite.
Hornblende as a Rock-Forming Mineral
• It is also found in metamorphic rocks such
as gneiss and schist.
• A few rocks consist almost entirely of hornblende.
• Amphibolite is the name given to metamorphic rocks
that are mainly composed of amphibole minerals.
Lamprophyre is an igneous rock that is mainly
composed
of
amphibole
and biotite with
a feldspar ground mass.
Identification of Hornblende
• Hornblende minerals as a group are relatively easy to
identify. The diagnostic properties are their dark color
(usually black) and two directions of excellent
cleavage that intersect at 124 and 56 degrees. The
angle between the cleavage planes and
hornblende's elongate habit can be used to
distinguish it from augite and other pyroxene minerals
that have a short blocky habit and cleavage angles
intersecting at about 90 degrees. The presence of
cleavage can be used to distinguish it from
black tourmaline that often occurs in the same rocks
• Identifying the individual members of the hornblende
group is difficult to impossible unless a person has the
skills and equipment to do optical mineralogy, x-ray
diffraction, or elemental analysis.
• The introductory student or the beginning mineral
collector can be satisfied to assign the name of
"hornblende" to a specimen.
Uses of Hornblende
• The mineral hornblende has very few uses. Its primary
use might be as a mineral specimen. However,
hornblende is the most abundant mineral in a rock
known as amphibolite which has a large number of
uses.
• It is crushed and used for highway construction and
as railroad ballast. It is cut for use as dimension stone.
The highest quality pieces are cut, polished, and sold
•
•
under the name "black granite" for use as building
facing,
floor
tiles,
countertops, and other
architectural uses.
Amphibolite is a coarse-grained metamorphic
rock that is composed mainly of green, brown, or
black amphibole minerals and plagioclase feldspar.
The
amphiboles
are
usually
members
of
the hornblende group.
It can also contain minor amounts of other
metamorphic
minerals
such
as biotite, epidote, garnet,
wollastonite, andalusite, staurolite, kyanite,
and
sillimanite.
Quartz, magnetite, and calcite can also be present in
small
amounts.
•
Hornblende has been used to estimate the depth of
crystallization of plutonic rocks. Those with low
aluminum content are associated with shallow
depths of crystallization, while those with higher
aluminum content are associated with greater
depths of crystallization. This information is useful in
understanding the crystallization of magma and also
useful for mineral exploration
• Intrusive
rocks or Plutonic
rocks
When magma never reaches the surface and cools
to form intrusions (dykes, sills etc) the resulting rocks
are called plutonic. Depending on their silica
content, they are called (in ascending order of silica
content) gabbro, diorite, granite and pegmatite. By
quantity, these are the by far most common rock
types. Most magmas actually never reach the
surface of the earth.
Physical Properties of Hornblende
Chemical
Classification
Color
Silicate
Streak
Luster
White, colorless - (brittle, often leaves
cleavage debris behind instead of a
streak)
Vitreous
Diaphaneity
Translucent to nearly opaque
Cleavage
Two directions intersecting at 124 and 56
degrees
Mohs Hardness
5 to 6
Specific Gravity
2.9 to 3.5 (varies
composition)
Diagnostic
Properties
Chemical
Composition
Crystal System
Cleavage, color, elongate habit
Uses
Very little industrial use
The Mica Group
Usually black, dark green, dark brown
depending
(Ca,Na)2–3 (Mg,Fe,Al)5(Al,Si)8 O22 (OH,F)2
Monoclinic
upon
The micas are a group of monoclinic minerals whose property
of splitting into very thin flakes is characteristic and easily
recognized. It is due to the perfect cleavage parallel to the
basal plane in mica crystals, which in turn results from the
layered atomic structure of the minerals.
The commonly occurring micas, muscovite (colorless or
slightly tinted) and biotite (dark brown to nearly black), are
described below.
• Six-sided, with pseudo-hexagonal symmetry
• Cleavage flakes are flexible, elastic, and transparent
Muscovite, KAl2 (Si3 Al) O10 (OH)2
• Form and cleavage as stated above. White in colour,
unless impurities are present to tint the mineral; pearly
lustre. H=2 to 2½ (easily cut with a knife). G=about 2.9
(variable).
• Muscovite occurs in granites and other acid rocks as
silvery crystals, from which flakes can be readily
detached by the point of a penknife; also, in some
gneisses and mica-schists. It is a very stable mineral,
and persists as minute flakes in sedimentary rocks
such as micaceous sandstones.
• The name sericite is given to secondary muscovite,
which may be produced by the alteration of
orthoclase. The mica of commerce comes from large
crystals found in pegmatite veins (p. l 06).
• In thin section: vertical sections (i.e., across the
cleavage) are often parallel-sided and show the
perfect cleavage (Fig. 4.17); basal sections appear
as 6-sided or irregular colourless plates. Alteration
uncommon.
• Mean R.I. = 1.59
• Biref: Strong (max. =0.04), giving bright pinks and
greens in vertical sections.
• Extinction: Straight, with reference to the cleavage.
Biotite, K(MgFeMSi3Al)O 10(OH)2
• Crystals are brown to nearly black in hand specimen;
single flakes are pale brown and have a sub-metallic
or pearly lustre. Form and cleavage as stated above.
H = 2½ to 3. G=2.8 to 3.1.
• Biotite occurs in many igneous rocks, e.g., granites,
syenites, diorites, and their lavas and dyke rocks, as
dark lustrous crystals, distinguished from muscovite by
their colour. Also, a common constituent of certain
gneisses and schists.
• In thin section: Sections showing the cleavage often
have two parallel sides and ragged ends (Fig. 4.17).
In some biotites, small crystals of zircon enclosed in
the mica have developed spheres of alteration
around themselves by radioactivity. These spheres in
section appear as small dark areas or 'haloes' around
the zircon and are pleochroic.
• Colour: Shades of brown and yellow in sections
across the cleavage, which are strongly pleochroic;
the mineral is. darkest (i.e. light absorption is a
maximum) when the cleavage is parallel to the
vibration direction of the polarizer. Basal sections
have a deeper tint and are only feebly pleochroic.
• Mean R.I. = about 1.64.
• Biref: Strong, about 0.05 (max.). Basal sections are
almost isotropic.
• Extinction: Parallel to the cleavage.
Alteration to green chlorite is common, when the
mineral loses its strong birefringence and polarizes in
light greys (see under Chlorite, p. 80).
Optical Properties:
R.I = Refractive Index
Biref = Birefringence
CLASSIFICATION OF ROCKS: IGNEOUS & SEDIMENTARY
ROCKS
• It is aggregate of mineral. They form a major part of the
earth’s crust
Rocks are divided into three major groups:
1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks
IGNEOUS ROCKS
Igneous rocks are formed by cooling and solidification of
magma.
Magma is hot, viscous, siliceous, melts, contains water vapor,
and gases. It comes from great
depth below the earth’s surface.
It is mainly composed of O, Si, Al, Fe, Na, Mg, Ca, and K.
• General characteristics of magma:
• Parent material of igneous rocks
• Forms from partial melting of rocks
• Magma at surface is called lava
CHEMICAL COMPOSITION OF IGNEOUS ROCKS
• Acid Magma – is rich in Si, Na, & K. Poor in Ca, Mg, & Fe.
• Basic Magma – is rich in Ca, Mg, & Fe. Poor in Si, Na, & K.
CLASSIFICATION OF IGNEOUS ROCKS
Over saturated
- contains high amount of Si & abundant quartz with alkali
feldspars
Saturated
- contains sufficient amount of Si with no quartz.
Under saturated
- contains less Si & high in alkali with aluminum oxides.
IGNEOUS ROCKS TEXTURES
Texture refers to the size, shape and arrangement of minerals’
grains and is an important characteristic of igneous rocks.
Grain size records cooling history. It all comes down to the
rate at which the rock cools. Other factors include the
diffusion rate, which is how atoms and molecules move
through the liquid.
The rate of crystal growth is another factor, and that's how
quickly new constituents come to the
surface of the growing crystal. New crystal nucleation rates,
which is how enough chemical components can come
together without dissolving, is another factor affecting the
texture.
DIFFERENT TEXTURES OF IGNEOUS ROCKS
1. Aphanitic Texture
- An aphanitic texture consists of an aggregate of very small
mineral grains, too small to be seen clearly with the naked
eye. Aphanitic textures record rapid cooling at or very near
Earth’s surface and are characteristic of extrusive (volcanic)
igneous rock.
2. Phaneritic Texture
- A phaneritic texture consists of an aggregate of large
mineral grains, easily visible without magnification. Phaneritic
textures record slow cooling within Earth and are
characteristic of intrusive (plutonic) igneous rocks.
3. Glassy Texture
- Very rapid cooling of lava produces a “glassy texture”. The
lava cools so quickly that atoms do not have time to arrange
in an ordered three dimensional network typical of minerals.
The result is natural glass, or obsidian.
4. Vesicular Texture
- Gases trapped in cooling lava can result in numerous small
cavities, vesicles, in the solidified rock.
5. Pyroclastic Texture
- Igneous rocks formed of mineral and rock fragments
ejected from volcanoes by explosive eruptions have
pyroclastic textures. The ejected ash and other debris
eventually settles to the surface where it is consolidated to
form a Pyroclastic igneous rock. Much of this material consists
of angular pieces of volcanic glass
measuring up to 2mm.
6. Porphyritic Texture
- Igneous rocks comprised of minerals of two or more
markedly different grain sizes have a porphyritic texture. The
coarser grains are called phenocrysts and the smaller grains
groundmass. Porphyritic textures result from changes in
cooling rate and include both aphanitic porphyrys and
phaneritic porphyrys.
FORMS OF IGNEOUS BODIES
1. Extrusive Igneous Bodies
- Volcanic (extrusive) igneous rocks form by cooling and
crystallization of lava or by consolidation of pyroclastic
material, such as volcanic ash, ejected from volcanoes.
2. Intrusive Igneous Bodies
- Plutonic (intrusive) igneous rocks form as magma cools and
crystallizes within Earth.
It is not possible to study magma directly. However, studying
lavas can tell us a lot.
• Magmas have a range of compositions
• Characterized by high temperatures
• Have the ability to flow
SEDIMENTARY ROCKS
Sedimentary rocks are the type of rocks that are formed by
the deposition of material at earth's
surface and within the bodies of rocks.
- Contributes about 8% of total volume of crust.
- Sedimentary rocks are those which have formed out of
sediments.
- The study of sedimentary rocks and rock strata provides
information about the subsurface that is useful for civil
engineering.
- Sediments are rock fragments which are product of
weathering.
- Weathering has already been defined as natural processes
of disintegration and
decomposition of rocks.
- Sediments, which have formed out of disintegration, are
loose materials of various
sizes like clay, sand, and pebbles.
FORMATION OF SEDIMENTARY ROCKS
Sedimentary rocks are formed at, or near the Earth’s surface
by accumulation and lithification of fragments of pre-existing
rocks or by precipitation from solution at normal surface
temperatures.
On the basis of their mode of formation, sedimentary rocks
are classified as:
1. Clastic sedimentary rocks
2. Bioclastic sedimentary rocks
3. Crystalline sedimentary rocks
1. Clastic Sedimentary Rocks
- Clastic sedimentary rocks are made up of pieces (clasts) of
pre-existing rocks. Pieces of rock are loosened by weathering,
then transported to some basin or depression where sediment
is trapped. If the sediment is buried deeply, it becomes
compacted and cemented, forming sedimentary rock
2. Bioclastic Sedimentary Rocks
- Such as coal, and some limestones are formed from the
accumulation of plant or animal debris.
- Organic sedimentary rocks are those containing large
quantities of organic molecules. Organic molecules contain
carbon, but in this context we are referring specifically to
molecules with carbon-hydrogen bonds, such as materials
from the soft tissues of plants
3. Crystalline Sedimentary Rocks
- are formed when dissolved materials precipitate from
solutions.
DISTINCTION BETWEEN IGNEOUS & SEDIMENTARY ROCKS
IGNEOUS ROCKS:
- Igneous rocks form when molten rock (magma or lava)
cools, crystallizes, and solidifies.
- Metamorphic rocks form from heat and pressure.
- Igneous and metamorphic rocks make up 90–95% of the top
16 km of the Earth's
crust by volume.
- Igneous rocks form at temperatures and pressures that
destroys fossil remnants.
- The structures of igneous rocks are large scale features,
which are dependent on several factors like:
o Composition of magma.
o Viscosity of magma.
o Temperature and pressure at which cooling and
consolidation takes place.
o Presence of gases and other volatiles.
- Igneous rocks are classified according to mode of
occurrence, texture, mineralogy,
chemical composition, and the geometry of the igneous
body
SEDIMENTARY ROCKS:
- Sedimentary rocks originate when particles settle out of
water or air, or by precipitation of minerals from water. They
accumulate in layers.
- Sedimentary rocks are formed from pressure, compaction
and cementation.
- The sedimentary rock cover of the continents of the Earth's
crust is extensive, but the total contribution of sedimentary
rocks is estimated to be only 8% of the total volume of the
crust.
- Fossils are most commonly found in sedimentary rock.
- Structures in sedimentary rocks can be divided into 'primary'
structures (formed during deposition) and 'secondary'
structures (formed after deposition). Structures are always
large-scale features that can easily be studied in the field.
- Based on the processes responsible for their formation,
sedimentary rocks can be subdivided into three groups:
clastic sedimentary rocks, bioclastic sedimentary rocks, and
crystalline sedimentary rocks
CLASSIFICATION OF ROCKS: METAMORPHIC
Introduction:
Metamorphic rocks have been modified by heat, pressure,
and chemical processes, usually while buried deep below
Earth's surface. Exposure to these extreme conditions has
altered the mineralogy, texture, and chemical composition of
the rocks. Metamorphic rocks arise from the transformation of
existing rock to new types of rock, in a process called
metamorphism. The original rock (protolith) is subjected to
temperatures greater than 150 to 200 °C (300 to 400 °F) and,
often, elevated pressure (100 megapascals (1,000 bar) or
more), causing profound physical or chemical changes.
During this process, the rock remains mostly in the solid state,
but gradually recrystallizes to a new texture or mineral
composition. The protolith may be a sedimentary, igneous, or
existing metamorphic rock. Metamorphic rocks make up a
large part of the Earth's crust and form 12% of the Earth's land
surface. They are classified by their protolith, their chemical
and mineral makeup, and their texture. They may be formed
simply by being deeply buried beneath the Earth's surface,
where they are subject to high temperatures and the great
pressure of the rock layers above. They can also form from
tectonic processes such as continental collisions, which
cause
horizontal
pressure,
friction,
and
distortion.
Metamorphic rock can be formed locally when rock is
heated by the intrusion of hot molten rock called magma
from the Earth's interior. The study of metamorphic rocks (now
exposed at the Earth's surface following erosion and uplift)
provides information about the temperatures and pressures
that occur at great depths within the Earth's crust. Some
examples of metamorphic rocks are gneiss, slate, marble,
schist, and quartzite. Slate and quartzite tiles are used in
building construction. Marble is also prized for building
construction and as a medium for sculpture. On the other
hand, schist bedrock can pose a challenge for civil
engineering because of its pronounced planes of weakness.
Metamorphic Minerals
Because every mineral is stable only within certain limits, the
presence of certain minerals in metamorphic rocks indicates
the approximate temperatures and pressures at which the
rock underwent metamorphosis. These minerals are known as
index minerals. Examples include sillimanite, kyanite,
staurolite, andalusite, and some garnet. Other minerals, such
as olivines, pyroxenes, hornblende, micas, feldspars, and
quartz, may be found in metamorphic rocks, but are not
necessarily the result of the process of metamorphism.
These minerals can also form during the crystallization of
igneous rocks. They are stable at high temperatures and
pressures and may remain chemically unchanged during the
metamorphic process.
Texture
Metamorphic rocks are typically more coarsely crystalline
than the protolith from which they formed. Atoms in the
interior of a crystal are surrounded by a stable arrangement
of neighboring atoms. This is partially missing at the surface of
the crystal, producing a surface energy that makes the
surface thermodynamically unstable. Recrystallization to
coarser crystals reduces the surface area and so minimizes
the surface energy. Although grain coarsening is a common
result of metamorphism, rock that is intensely deformed may
eliminate strain energy by recrystallizing as a fine-grained
rock called mylonite. Certain kinds of rock, such as those rich
in quartz, carbonate minerals, or olivine, are particularly
prone to form mylonites, while feldspar and garnet are
resistant to mylonitization.
Foliation
Many kinds of metamorphic rocks show a distinctive layering
called foliation (derived from the Latin word folia, meaning
"leaves"). Foliation develops when a rock is being shortened
along one axis during recrystallization. This causes crystals of
platy minerals, such as mica and chlorite, to become rotated
such that their short axes are parallel to the direction of
shortening. This results in a banded, or foliated, rock, with the
bands showing the colors of the minerals that formed them.
Foliated rock often develops planes of cleavage. Slate is an
example of a foliated metamorphic rock, originating from
shale, and it typically shows well-developed cleavage that
allows slate to be split into thin plates. The type of foliation
that develops depends on the metamorphic grade. For
instance, starting with a mudstone, the following sequence
develops with increasing temperature: The mudstone is first
converted to slate, which is a very fine-grained, foliated
metamorphic rock, characteristic of very low-grade
metamorphism. Slate in turn is converted to phyllite, which is
fine-grained and found in areas of low-grade metamorphism.
Schist is medium to coarse-grained and found in areas of
medium grade metamorphism. High-grade metamorphism
transforms the rock to gneiss, which is coarse to very coarsegrained.
Rocks that were subjected to uniform pressure from all sides,
or those that lack minerals with distinctive growth habits, will
not be foliated. Marble lacks platy minerals and is generally
not foliated, which allows its use as a material for sculpture
and architecture.
Classification
Metamorphic rocks are one of the three great divisions of all
rock types, and so there is a great variety of metamorphic
rock types. In general, if the protolith of a metamorphic rock
can be determined, the rock is described by adding the
prefix meta- to the protolith rock name. For example, if the
protolith is known to be basalt, the rock will be described as a
metabasaltic. Likewise, a metamorphic rock whose protolith
is known to be a conglomerate will be described as a
metaconglomerate. For a metamorphic rock to be classified
in this manner, the protolith should be identifiable from the
characteristics of the metamorphic rock itself, and not
inferred from other information.
Under the British Geological Society classification system, if all
that can be determined about the protolith is its general
type, such as sedimentary or volcanic, the classification is
based on the mineral mode (the volume percentages of
different minerals in the rock). Metasedimentary rocks are
divided into carbonate-rich rock (metacarbonates or
calcsilicate-rocks) or carbonate-poor rocks, and the latter
are further classified by the relative abundance of mica in
their composition. This ranges from low-mica psammite
through semipellite to high-mica pellite. Psammites
composed mostly of quartz are classified as quartzite.
Metaigneous rocks are classified similarly to igneous rocks, by
silica content, from meta-ultramafic-rock (which is very low in
silica) to metafelsic-rock (with a high silica content).
Hazards
Varieties
Schistose bedrock can pose a challenge for civil engineering
because of its pronounced planes of weakness. A hazard
may exist even in undisturbed terrain. On August 17, 1959, a
magnitude 7.2 earthquake destabilized a mountain slope
near Hebgen Lake, Montana, composed of schist. This
caused a massive landslide that killed 26 people camping in
the area. Metamorphosed ultramafic rock contains
serpentine group minerals, which includes varieties of
asbestos that pose a hazard to human health.
IGNEOUS ROCKS
GABBRO
Minerals
Essential minerals are a plagioclase (generally
labradorite) and a monoclinic pyroxene (augite or diallage).
The plagioclase composition reflects the high CaO and low
Na2O content in gabbro (see analysis, p. 100). Other minerals
which may be present in different gabbros are hypersthene,
olivine, hornblende, biotite, and sometimes nepheline.
Ilmenite, magnetite, and apatite are common accessories.
Texture
Coarsely crystalline, rarely porphyritic, sometimes with
finer modifications. Hand specimens appear mottled dark
grey to greenish-black in colour because of the large mafic
content. Under the microscope the texture appears as
interlocking crystals (Fig. 5.19).
Varieties
•
•
•
Coarse to medium-grained, rarely porphyritic. In hand
specimens’ minerals can usually be distinguished with the aid
of a lens. Under the microscope minerals show interlocking
outlines, the mafic minerals tending to be idiomorphic
(=exhibit a regular shape).
Norite is a variety containing essentially hypersthene
instead of augite, i.e. a hypersthene-labradorite rock,
and is of common occurrence.
Troctolite has olivine and plagioclase (no augite)
Quartz-gabbro contains a little interstitial quartz,
derived from the last liquid to crystallize from a
magma with slightly higher silica content than normal
DIORITE
Diorite is related to granite, and by increase of silica
content and the incoming of orthoclase grades into the acid
rocks,
•
•
Quartz-diorite (the amount of quartz is much less than
in granite) is perhaps more common than diorite as
defined above.
Fine-grained varieties are called microdiorite.
PEGMATITES
Pegmatites are very coarse-grained vein rocks that
represent the last part of a granitic magma to solidify. The
residual magmatic fluids are rich in volatile constituents,
which contain the rarer elements in the magma. Thus in
addition to the common minerals quartz, alkali feldspar and
micas, large crystals of less common minerals such as beryl,
topaz, and tourmaline are found in pegmatities. Also residual
fluids carrying other rare elements, e.g. lithium, cerium,
tungsten, give minerals in the pegmatites that can be worked
for their extraction, such as the lithium pyroxene spodumene,
the cerium phosphate monazite and wolfram. The mica used
in industry - mainly muscovite and phlogopite (q.v), is
obtained from pegmatites; individual crystals may be many
centimetres across, yielding large mica plates. Canada,
India, and the United States produce mica from such sources.
Pegmatites are found in the outer parts of intrusive granites
and also penetrating the country-rocks.
Dolerite
The chemistry of this intrusive rock corresponds to gabbro but
its texture is finer. Dolerite forms dykes, sills, and other
intrusions. The rock is dark grey in color, except where its
content of feldspar is greater than average. Dolerite is
important as a road-stone for surfacing because of its
toughness, and its capacity for holding a coating of bitumen
and giving a good 'bind'. In its un-weathered state dolerite is
one of the strongest of the building stones and used for vaults
and strong-rooms, as in the Bank of England.
Minerals
plagioclase, pyroxene, hornblende and quartz.
Texture
Medium to fine-grained; some dolerites have a coarser
texture, when the lath-like shape of the feldspar is less
emphatic and the rock tends towards a gabbro. When the
plagioclase 'laths' are partly or completely enclosed in augite
the texture is called ophitic; this interlocking of the chief
components gives a very strong, tough rock.
thus: diorite -> quartz diorite -> granodiorite -> granite.
Minerals
Plagioclase (andesine) and hornblende; a small amount of
biotite or pyroxene, and a little quartz may be present, and
occasional orthoclase. Accessories include Fe-oxides, apatite
and sphene. The dark minerals make up from 15% to 40% of
the rock, and hand specimens are less dark than gabbro.
Texture
Varieties
Normal dolerite = labradorite + augite •+• iron oxides; if
olivine is present the term olivine-dolerite is used. Much
altered dolerites, in which both the feldspars and mafic
minerals show alteration products are called diabase, though
in America the term is often used synonymously with the British
usage of dolerite.
DOLERITE & BASALT
(PETROLOGY)
Basalt
Basalt is a dark, dense-looking rock, often with small
porphyritic crystals, and weathering to a brown colour on
exposed surfaces. It is the commonest of all lavas, the basalt
flows of the world being estimated to have five times the
volume of all other extrusive rocks together. Basalt also forms
small intrusions in form of dyke and/or thin sill.
Minerals
Essentially
plagioclase
(labradorite)
and
augite;
but some basalts
have a
more
calcic
plagioclase. Olivine
occurs
in many basalts and
may
show alteration to
serpentine.
Magnetite
and
ilmenite
are
common accessories; if vesicles are present they may be
filled with calcite, chlorite, chalcedony, and other secondary
minerals. Nepheline, leucite, and analcite are found in
basalts with a low content of silica.
basalt glass, or tachylite, is formed by the rapid cooling.
Varieties
Basalt and olivine-basalt are abundant; varieties containing
feldspathoids include nepheline-basalt
and leucite-basalt (e.g. the lavas from Vesuvius). Soda-rich
basalts in which the plagioclase is mainly albite
are called spilites, and often show 'pillow-structure' in the
mass, resembling a pile of sacks; they are erupted on the sea
floor. Their rapid cooling in the sea prevents the minerals
crystallized from achieving chemical equilibrium; they are
reactive and alter readily. Between the pillows are baked
marine sediments, often containing chert and jasper (SiO2).
These features of pillow lavas make them a most unsuitable
form of basalt for concrete aggregate.
Some of the great flows of basalt in different parts of the
world have been referred to earlier; their virtually constant
composition suggests a common source, the basaltic layer of
the Earth’s crust.
Calcite
•
•
•
Texture
Fine-grained or partly glassy; hand specimens appear eventextured on broken, unless the rock is porphyritic or vesicular;
small porphyritic crystals of olivine or augite may need some
magnification for identification. Under the microscope the
texture is microcrystalline to cryptocrystalline or partly glassy.
At the chilled margins of small intrusions a selvedge of black
•
•
•
•
•
•
•
Calcite is a rock-forming mineral with a chemical
formula of CaCO3, a white insoluble powder-like
substance which occurs naturally in minerals, chalk,
marble, limestones, calcite, shells, pearls, etc.
It is extremely common and found throughout the
world
in sedimentary, metamorphic,
and igneous rocks. Some geologists consider it to be
a "ubiquitous mineral" - one that is found everywhere.
Calcite
is
the
principal
constituent
of limestone and marble. These rocks are extremely
common and make up a significant portion of Earth's
crust. They serve as one of the largest carbon
repositories on our planet. Limestone, a sedimentary
rock forms from both the chemical precipitation of
calcium carbonate and the transformation of shell,
coral, fecal and algal debris into calcite during
diagenesis. It also forms as a deposit in caves from
the precipitation of calcium carbonate Marble is a
metamorphic rock formed after limestone is
subjected to heat and pressure.
PHYSICAL PROPERTIES:
Chemical classification: CARBONATE
Color: USUALLY WHITE BUT ALSO COLORLESS, GRAY,
RED, GREEN, BLUE, YELLOW, BROWN, ORANGE
Streak: WHITE
Luster: VITREOUS
Diaphaneity: TRANSPARENT TO TRANSLUCENT
Cleavage:
PERFECT,
RHOMBOHEDRAL,
THREE
DIRECTIONS
Mohs hardness: 3
•
•
•
•
•
Specific gravity: 2.7
Diagnostic properties: RHOMBOHEDRAL CLEAVAGE,
POWDERED FORM EFFERVESCES WEAKLY IN DILUTE
HCL, CURVED CRYSTAL FACES AND FREQUENT
TWINNING
Chemical composition: CaCO3
Crystal system: HEXAGONAL
USES:
•
in Construction - primary consumer of calcite in the
form of limestone and marble
- These rocks have been used as dimension stones and in
mortar for thousands of years. Limestone blocks were the
primary construction material used in many of the pyramids
of Egypt and Latin America. Today, rough and polished
limestone and marble are still an important material used in
prestige architecture. Modern construction uses calcite in the
form of limestone and marble to produce cement and
concrete. These materials are easily mixed, transported, and
placed in the form of a slurry that will harden into a durable
construction material. Concrete is used to make buildings,
highways, bridges, walls, and many other structures.
•
in Acid Neutralization - limestones and marbles have
been crushed and spread on fields as an acidneutralizing soil treatment. They are also heated to
produce lime that has a much faster reaction rate in
the soil.
Calcite is used as an acid neutralizer in the chemical industry.
In areas were streams are plagued with acid mine drainage,
crushed limestone is dispensed into the streams to neutralize
their waters.
metamorphosed severely, some of their carbon
dioxide is released and returned to the atmosphere
• Other - Powdered calcite is often used as a white
pigment or "whiting." Some of the earliest paints were
made with calcite. It is a primary ingredient in
whitewash, and it is used as an inert coloring
ingredient of paint.
Other - Pulverized limestone and marble are
often used as a dietary supplement in animal
feed.
-- suitable as a low-hardness abrasive. It is softer than the
stone, porcelain, and plastic surfaces found in kitchens and
bathrooms but more durable than dried food and other
debris that people want to remove. Its low hardness makes it
an effective cleaning agent that does not damage the
surface being cleaned.
- used as a mine safety dust. This is a nonflammable dust that
is sprayed onto the walls and roofs of underground coal
mines to reduce the amount of coal dust in the air (which
can be an explosion hazard). The mine safety dust adheres to
the wall of the mine and immobilizes the coal dust. Its white
color aids in illumination of the mine. It is the perfect material
for this use.
Garnet
•
•
Calcium carbonate derived from high-purity limestones or
marbles is used in medicine. Mixed with sugar and flavoring,
calcium carbonate is made into chewable tablets used in
the neutralization of stomach acids. It is also an ingredient in
numerous medications used to treat digestive and other
ailments
•
•
•
Sorbents - Sorbents are substances that can
"capture" another substance. Limestone is often
treated and used as sorbent material during the
burning of fossil fuels. Calcium carbonate reacts with
sulfur dioxide and other gases in the combustion
emissions, absorbs them, and prevents them from
escaping to the atmosphere
Monuments and Statuary - Marble is an attractive
and easily worked rock that has long been used for
monuments and sculptures. Its lack of significant
porosity allows it to stand up well to freeze-thaw
action outdoors, and its low hardness makes it an
easy stone to work. It has been used in projects as
large as the pyramids and as small as a figurine. It is
widely used as cemetery markers, statues, mantles,
benches, stairways, and much more.
Carbon Dioxide Repository - The process of limestone
formation removes carbon dioxide from the
atmosphere and stores it away for long periods of
time. This process has been occurring for millions of
years - producing enormous volumes of stored
carbon dioxide. When these rocks are weathered,
used to neutralize acids, heated to make cement or
•
•
Garnet is the name used for a large group of rockforming minerals. These minerals share a common
crystal structure and a generalized chemical
composition of X3Y2(SiO4 )3 . In that composition, "X"
can be Ca, Mg, Fe 2+ or Mn2+, and "Y" can be Al, Fe 3+,
Mn3+, V 3+ or Cr 3+.
These minerals are found throughout the world
in metamorphic, igneous, and sedimentary rocks.
Most garnet found near Earth's surface forms when a
sedimentary rock with a high aluminum content,
such as shale, is subjected to heat and pressure
intense enough to produce schist or gneiss. Garnet is
also found in the rocks of contact metamorphism,
subsurface magma chambers, lava flows, deepsource volcanic eruptions, and the soils and
sediments formed when garnet-bearing rocks are
weathered and eroded.
Most people associate the word "garnet" with a
red gemstone; however, they are often surprised to
learn that garnet occurs in many other colors and
has many other uses.
Garnet Physical and Chemical Properties - The most
commonly encountered minerals in the garnet group
include almandine, pyrope, spessartine, andradite,
grossular, and uvarovite. They all have a
vitreous luster,
a
transparent-to-translucent
diaphaneity, a brittle tenacity, and a lack of
cleavage. They can be found as individual crystals,
stream-worn pebbles, granular aggregates, and
massive occurrences. Their chemical composition,
specific gravity, hardness, and colors are listed
below.
Garnet Minerals
Mineral
Composition
Specific
Gravity
Hardness Colors
Almandine Fe3 Al2 (SiO4 )3
4.20
7 - 7.5
red, brown
Pyrope
3.56
7 - 7.5
red
purple
to
to
to
Mg3 Al2 (SiO4 )3
Spessartine Mn3 Al2 (SiO4 )3
4.18
6.5 - 7.5
orange
red
brown
Andradite
Ca3 Fe2 (SiO4 )3
3.90
6.5 - 7
green,
yellow,
black
Grossular
Ca3 Al2 (SiO4 )3
3.57
6.5 - 7.5
green,
yellow, red,
pink, clear
Uvarovite
Ca3 Cr 2 (SiO4 )3
3.85
6.5 - 7
green
The compositions listed above are for end members of
several solid solution series. There are a number of other
garnet minerals that are less frequently encountered and not
as important in industrial use. They include goldmanite,
kimzeyite, morimotoite, schorlomite, hydrogrossular, hibschite,
katoite, knorringite, majorite, and calderite.
•
Uses of Garnet
o Garnet as an Industrial Mineral
Garnet Abrasives
The first industrial use of garnet was as an abrasive. Garnet is
a relatively hard mineral with a hardness that ranges
between 6.5 and 7.5 on the Mohs Scale. That allows it to be
used as an effective abrasive in many types of
manufacturing. When crushed, it breaks into angular pieces
that provide sharp edges for cutting and sanding. Small
granules of uniform size are bonded to paper to produce a
reddish color sandpaper that is widely used in woodworking
shops. Garnet is also crushed, screened to specific sizes, and
sold as abrasive granules and powders. In the United States,
New York and Idaho have been important sources of
industrial garnet for abrasives.
Waterjet Cutting
The largest industrial use of garnet in the United States is in
waterjet cutting. A machine known as a waterjet cutter
produces a high-pressure jet of water with entrained abrasiv e
granules. When these are directed at a piece of metal,
ceramic, or stone, a cutting action can occur that produces
very little dust and cuts at a low temperature. Waterjet cutters
are used in manufacturing and mining.
Abrasive Blasting
Garnet granules are also used in abrasive blasting
(commonly known as "sand blasting"). In these processes, a
tool propels a stream of abrasive granules (also known as
"media") against a surface using a highly pressurized fluid
(usually air or water) as a propellant. Abrasive blasting is done
in order to smooth, clean, or remove oxidation products from
metals, brick, stone, and other materials. It is usually much
faster than sanding by hand or with a sanding machine. It
can clean small and intricate surfaces that other cleaning
methods would miss. Abrasives of various hardnesses can be
used to clean a surface of greater hardness, without
damaging the surface.
Filtration
Garnet granules are often used as a filter media. Small garnet
particles are used to fill a container through which a liquid
flows. The pore spaces of the garnet are small enough to
allow passage of the liquid but are too small to allow
passage of some contaminant particles, which are filtered
from the flow. Garnet is suited for this use because it is
relatively inert and has a relatively high specific gravity.
Garnet granules, crushed and graded to about 0.3
millimeters in size, can be used to filter out contaminant
particles as small as a few microns in diameter. Garnet's high
specific gravity and high hardness reduce bed expansion
and particle abrasion during backflushing.
•
Garnet as a Geological Indicator Mineral
Although most of the garnets found at Earth's surface have
formed within the crust, some garnets are brought up from
the mantle during deep-source volcanic eruptions. These
eruptions entrain pieces of mantle rock known as "xenoliths"
and deliver them to the surface in a structure known as a
"pipe."
These
xenoliths
are
the
source
of
most diamonds found at or near Earth's surface.
Although xenoliths contain diamonds, they often contain a
tremendous number of garnets for every diamond, and those
garnets are generally larger in size. These deep-source
garnets are very different from the garnets that form in the
crust at shallow depth. So, a good way to prospect for
diamonds is to look for these unique garnets. The garnets
serve as "indicator minerals" for geologists exploring for
diamond deposits. As the xenoliths weather, their garnets are
liberated in large numbers. These unusual garnets then move
downslope in soils and streams.
•
Garnets as Gemstones
Garnet has been used as a gemstone for over 5000 years. It
has been found in the jewelry of many Egyptian burials and
was the most popular gemstone of Ancient Rome. It is a
beautiful gem that is usually sold without treatment of any
kind. It is also durable and common enough that it can be
used in jewelry at a relatively low cost.
It serves as a birthstone for the month of January and is a
traditional gem given on a second anniversary. Gem-quality
garnets occur in every color - with red being the most
common and blue garnets being especially rare.
COAL
At various times in the geologic past, the Earth had dense
forests in low-lying wetland areas. Due to natural processes
such as flooding, these forests were buried under the soil. As
more and more soil deposited over them, they were
compressed. The temperature also rose as they sank deeper
and deeper.
Under high pressure and high temperature, dead vegetation
was slowly converted to coal. As coal contains mainly
carbon, the conversion of dead vegetation into coal is called
carbonization.
CHARCOAL
Charcoal is mostly pure carbon, called char, made by
cooking wood in a low oxygen environment, a process that
can take days and burns off volatile compounds such as
water, methane, hydrogen, and tar.
You make charcoal by heating wood to high temperatures in
the absence of oxygen. This can be done with ancient
technology: build a fire in a pit, then bury it in mud. The results
is that the wood partially combusts, removing water and
impurities and leaving behind mostly pure carbon.
Origin and Occurrence of Coal in India
History of Coal in India(Pre Independence)
• Coal in India was first mined in 1774 with John Sumner
and Suetonius Heatly of the East India Company.
• The growth remained slow for nearly a century due
to low demand but later on, the demand increased
due to introduction of Steam Locomotives in 1853.
• Coal production rose steadily by 1920 and boosted
by demand due to World War I.
A steam locomotive is a type of railway locomotive that
produces its pulling power through a steam engine. These
locomotives are fueled by burning combustible material—
usually coal.
History of Coal in India(Post Independence)
• In the regions of British India known as Bengal, Bihar
and Odisha, the Indians pioneered Indian
involvement in coal mining from 1894.
• They broke monopolies held by British and other
Europeans and established many collieries.
Seth Khora Ramji was the first Indian to break the British
Monopoly.
Collieries
A coal mine and the buildings and equipment associated
with it.
History of Coal in India(Nationalization)
• The National Coal Development Corporation was
established in 1956.
• Coal mining in phases was nationalized, coking coal
mines in 1971 to 1972 and non-coking coal mines in
1973.
• All coal mines were nationalized on May 1, 1973 and
four decades later the government permitted the
private companies to mine coals for their own
plants.
• In 1975, Eastern Coalfields Limited, a subsidiary of
Coal India Limited, was formed and took over all the
earlier private collieries.
The National Coal Development
The National Coal Development Corporation (NCDC) was
established in 1956 with the aim of increasing coal production
efficiently by systematic and scientific development of the
coal industry.
Coking is the heating of coal in the absence of oxygen to a
temperature above 600 °C to drive off the volatile
components of the raw coal, leaving a hard, strong, porous
material of high carbon content called coke.
A coking coal is that coal which on heating in absence of air
leaves a solid residue. A non-coking coal also leaves a solid
coherent residue which may not possess the physical &
chemical properties of the coke.
In March 2015, the government permitted private companies
to mine coal for use in their own cement, steel, power or
aluminium plants.
History of Coal in India(Denationalization)
• On February 20, 2018, the Cabinet Committee on
Economic Affairs permitted private firms to enter
commercial coal mining industry in India.
• Coking Coal Mines(Nationalization) Act, 1972 and
the Coal Mines(Nationalization) Act, 1973 were
repealed by the Repealing and Amending(Second)
Act,2017 on January 8, 2018.
Under the new policy, mines will be auctioned to the firm
offering the highest per tonne price. The move broke the
monopoly over commercial mining that state-owned Coal
India has enjoyed since nationalization in 1973.
5 Highest Reserves of Coal in India
• 1. Jharkhand - 83.15 billion tonnes
Located in north-east India, tops the list of India’s
coal reserves at more than 26% and production.
• 2. Odisha – 79.30 billion tonnes
Located on the east coast of India. It has more than
24% of the country’s total reserves and is responsible for
about 15% of India total production.
•
3. Chhattisgarh – 57 billion tonnes
Central Indian state that holds about 17% of the
country’s coal deposits and is the third largest in terms of coal
reserves.
• 4. West Bengal – 31.67 billion tonnes
Holds about 11% of India’s total coal reserves.
• 5. Madhya Pradesh – 27.99 billion tonnes
Holds 8% of country’s coal deposits/coal reserve.
4 Main Types of Coal in India
• 1. Anthracite
It is the highest quality hard coal. It is found in parts of
Jammu
• 2. Bituminous
This coal has been buried deep and subjected to
increased temperatures. It is the most popular coal in
commercial use. Metallurgical coal is high grade bituminous
coal which has a special value for smelting iron in blast
furnaces and Kashmir.
• 3. Lignite
It is a low grade brown coal, which is soft with high
moisture content. The lignite reserves are in Neyveli in Tamil
Nadu. It is used for the generation of electricity.
• 4. Peat
Decaying plants in swamps produce peat, which has
low carbon content and high moisture content resulting in
low heating capacity.
GEO REPORT
Petroleum
Petroleum, also called crude oil, is a fossil fuel. Like coal and
natural gas, petroleum was formed from the remains of
ancient marine organisms, such as plants, algae, and
bacteria. Over millions of years of intense heat and pressure,
these organic remains (fossils) transformed into carbon-rich
substances we rely on as raw materials for fuel and a wide
variety of products.
Oil Location
Engineers use sophisticated equipment, including satellites, to
find potential oil reserves beneath the earth or the ocean.
Crude oil is usually black or dark brown, but can also be
yellowish, reddish, tan, or even greenish. Variations in color
indicate the distinct chemical compositions of different
supplies of crude oil. Petroleum that has few metals or sulfur,
for instance, tends to be lighter (sometimes nearly clear).
Chemistry and Classification of Crude Oil
Chemistry
Crude oil is composed of hydrocarbons, which are mainly
hydrogen (about 13% by weight) and carbon (about 85%).
Other elements such as nitrogen (about 0.5%), sulfur (0.5%),
oxygen (1%), and metals such as iron, nickel, and copper
(less than 0.1%) can also be mixed in with the hydrocarbons in
small amounts.
The way molecules are organized in the hydrocarbon is a
result of the original composition of the algae, plants, or
plankton from millions of years ago. The amount of heat and
pressure the plants were exposed to also contributes to
variations that are found in hydrocarbons and crude oil.
Due to this variation, crude oil that is pumped from the
ground can consist of hundreds of different petroleum
compounds. Light oils can contain up to 97% hydrocarbons,
while heavier oils and bitumens might contain only 50%
hydrocarbons and larger quantities of other elements. It is
almost always necessary to refine crude oil in order to make
useful products.
Oil Reserves
Oil reserves are reservoirs of petroleum trapped by rock deep
beneath the earth. Oil reserves are found all over the world,
and measured in barrels (bbl). A barrel of oil is about 100–200
liters (26–53 gallons).
Wildcatters
"Wildcatting" is the risky practice of drilling for petroleum in an
area where there are no proven oil reserves. Some of the
most famous wildcat operations took place around the turn
of the 20th century in rural California above, where enormous
oil reserves were discovered and working-class miners
became multi-millionaires.
Developmental Drilling
Developmental drilling is the safer practice of drilling where
oil reserves have already been found. These wells near Long
Beach, California, were established well after wildcatters
discovered petroleum in the area decades earlier.
Directional Drilling
Directional drilling is a relatively new technique of extracting
petroleum. Directional drilling involves drilling vertically to a
known source of oil, then veering the drill bit at an angle to
access additional resources.
Thirsty Bird
Most of the nations with the largest oil reserves belong to the
Organization of Petroleum Exporting Countries (OPEC).
According to OPEC, more than 80% of the world's proven oil
reserves are located in OPEC member countries, with the bulk
of OPEC oil reserves in the Middle East.
Extracting petroleum involves large, complex machinery. On
land, this machinery is called an oil rig. Oil rigs have both
drilling equipment and pumping equipment. One of the most
familiar pumps is the pumpjack, often nicknamed the
nodding donkey or "thirsty bird." This thirsty bird is painted to
look like a bustard, native to Bahrain, where this pumpjack is
found.
Classifying Petroleum
Oil Refinery
There are many ways to classify petroleum. One is
geography. Three primary sources of petroleum set reference
points for ranking and pricing other oil supplies: Brent Crude
(found beneath the North Sea), West Texas Intermediate
(drilled in Texas, such as here, in Padre Island), and Dubai and
Oman. Other ways of classifying petroleum are by API gravity,
which measures oil density to that of water, and by
petroleum's sulfur content. It is this classification that describes
petroleum as "sweet" (low sulfur) or "sour" (high sulfur).
Refining petroleum is the process of converting crude oil into
more useful products, such as fuel or asphalt. Refineries
remove "impurities," such as sulfur and sand, from petroleum.
This refinery in the province of Alberta, Canada, processes oil
from the region's "tar sands."
ALL ABOUT EXTRACTION
These nations have the world’s largest proven oil reserves.
1. Saudi Arabia
Prosthetic Limbs
Petroleum products are used in everything from gel capsules
to bubble gum. The plastics used in Lt. Col. Greg Gadson's
sophisticated prosthetic legs are made possible by
petroleum.
2.
3.
4.
5.
Venezuela
Canada
Iran
Iraq
Leading Petroleum Producers
1. Saudi Arabia
2. Russia
3. United States
4. Iran
5. China
Petroleum and Natural Gas basins in India
• The Upper Assam Basin
• The Western Bengal Basin
• The Western Himalayan Basin
• The Rajasthan Saurashtra-Kachchh Basin
Leading Petroleum Consumers
1. United States
2. China
3. Japan
4. India
5. Saudi Arabia
OCCURRENCE IN INDIA
Importance of Petroleum
(a) Petroleum is the major energy source in India.
(b) Provides fuel for heat and lighting.
(c) Provides lubricant for machinery.
(d) Provides raw material for several manufacturing industries.
(e) Petroleum refineries act as nodal industry for
synthetic, textile, fertilizer and chemical industries.
Its occurrence:
(a) Most of the petroleum occurrences in India are
associated with anticlines and fault traps.
(b) In regions of folding, anticline or domes, it occurs where
oil is trapped in the crest of the upfold.
(c) Petroleum is also found in fault traps between porous and
non-porous rocks.
Origin and Occurrence of Petroleum:
Petroleum has an organic origin and is found in sedimentary
basins, shallow depressions and in the seas (past and
present). Most of the oil reserves in India are associated with
anticlines and fault traps in the sedimentary rock formations
of tertiary times, about 3 million years ago. Some recent
sediment, less than one million years also show evidence of
incipient oil.
Oil and natural gas originated from animal or vegetable
matter contained in shallow marine sediments, such as sands,
silts and clays deposited during the periods when land and
aquatic life was abundant in various forms, especially the
minor microscopic forms of flora and fauna.
As already mentioned, oil as well as natural gas in India
occur in sedimentary rocks. About 14.1 lakh sq km or about
42 per cent of the total area of the country is covered with
sedimentary rocks out of which about 10 lakh sq km form
marine basins of Mesozoic and Tertiary times.
Besides, the country has offshore areas having Mesozoic and
Tertiary rocks of marine origin covering an area of 2.5 lakh sq
km up to a depth of 100 metre and another area of 0.7 lakh
sq km upto a depth between 100 and 200 metre. Thus the
total continental shelf of probable oil bearing rocks amounts
to 3.2 lakh sq km
• The Northern Gujarat Basin
• The Ganga Valley Basin
• The Coastal Tamil Nadu, Andhra & Kerala Basin
• The Andaman and Nicobar Coastal Basin
• Offshore of the Khambat, Bombay High & Bassein
Petroleum
Petroleum or mineral oil is the next major energy source in
India after coal. It provides fuel for heat and lighting,
lubricants for machinery and raw materials for a number of
manufacturing industries. Petroleum refineries act as a “nodal
industry” for synthetic textile, fertiliser and numerous chemical
industries. Most of the petroleum occurrences in India are
associated with anticlines and fault traps in the rock
formations of the tertiary age. In regions of folding, anticlines
or domes, it occurs where oil is trapped in the crest of the
unfold. The oil bearing layer is a porous limestone or
sandstone through which oil may flow. The oil is prevented
from rising or sinking by intervening non-porous layers.
Petroleum occurs in association with natural gas and water. It
lies in the sedimentary rock formations like sandstone,
limestone or shale. It is believed that petroleum has been
derived from plant and animal life hurried millions of years
ago.
Reserves:
Although India has vast areas covered by sedimentary rocks,
structures containing oil are not in proportion to the expanses
of these rocks and are found in limited situations. The Indian
Mineral Year Book 1982 estimated a reserve of 468 million
tonnes of which 328 million tonnes was available in Mumbai
High. In 1984 the reserves were estimated at 500 million
tonnes.
The Indian Petroleum and Natural Gas Statistics put the total
reserves of crude oil at 581.43 million tonnes in 1986-87. The
prognosticated hydrocarbon resource base in Indian
sedimentary basins including deep water has been estimated
at about 28 billion tonnes.
Of this only about one-fourth i.e., 7.2 billion tonnes of in place
hydrocarbon reserves have been established as on 1 April,
2002. About 70 per cent of the established hydrocarbon
reserves is oil and rest is gas. The recoverable hydrocarbon
reserves are of the order of 2.6 billion tonnes.
Production:
India was a very insignificant producer of petroleum at the
time of Independence and remained so till Mumbai High
started production on a large scale. In fact, off-shore
production did not start till the mid 1970s and the entire
production was received from on-shore oil fields.
In 1980-81 about half of the production of crude oil came
from on-shore fields while the remaining half was received
from the off-shore resources. After that juncture, the off-shore
production increased at a much faster rate than the on-shore
production. For more than two decades from 1990-91 to
2003-04, about two-thirds of production of crude oil is
provided by the off-shore fields.
The production touched the all time peak of 34.09 million
tonnes in 1989-90 but slumped to 30.44 million tonnes in 199192, 28.46 million tonnes in 1992-93 and further to 27.03 million
tonnes in 1993-94. Sharp drop of production by over 7 million
tonnes in a short span of four years is ascribed to overworking
of Mumbai High oil wells. This was a dangerous trend and was
to be reversed at all costs.
4 Categories of Mineral Formation
IGNEOUS or MAGMATIC in which minerals crystallize
from a melt or formed by the cooling and solidification
of molten earth material.
The word “igneous” is derived from the Latin word
“ignis” that means fire. In other words, igneous rocks
are formed by the cooling of the magma that has
different crystalline patterns and can form different
minerals.
They are formed by the cooling down and solidification
of magma or lava. They can usually be seen in the crust
or mantle.
Examples:
•
•
•
•
Fledspars
Quartz
Obsidian
Basalt
PROCESS OF FORMATION OF MINERALS COAL AND
PETROLEUM
What are minerals?
As defined in Merriam-Webster minerals are: "any of
various naturally occurring homogeneous substances
(such as stone, coal, salt, sulfur, sand, petroleum,
water, or natural gas) obtained usually from the
ground"
Minerals can be classified in two base on where they
came from. The two classifications are metallic and
non-metallic minerals.
SEDIMENTARY in which minerals are the result of
sedimentation, a process whose raw materials are
particles from other rocks that have undergone
weathering or erosion.
Sedimentary minerals are formed when disintegrated
parts of other kinds of minerals joined together. These
kinds of minerals have two types; the clastic and
chemical sediments.
Examples:
•
•
•
•
Calcite
Dolomite
Flint
Pyrite
METAMORPHIC in which new minerals form at the
expense of earlier ones owing to the effects of
changing—usually increasing—temperature or
pressure or both on some existing rock type.
They are formed by the rearrangement of mineral
components due to pressure or chemical reaction
when combining the fluids that they have absorbed.
Unlike igneous, they are formed by making the
minerals more densed or compact. Metamorphic
minerals have two types which foliated and nonfoliated.
years ago. These fossil fuels are then refined into
usable substances such as petrol, kerosene, etc.
How are Coals formed?
Coal is under the sedimentary category. The conditions
that would eventually create coal began to develop
about 300 million years ago, during the Carboniferous
period. During this time, the Earth was covered in
wide, shallow seas and dense forests. The seas
occasionally flooded the forested areas, trapping
plants and algae at the bottom of a swampy wetland.
Examples:
•
•
•
•
Slate
Marble
Quartzite
Granite
HYDROTHERMAL in which minerals are chemically
precipitated from hot solutions within Earth.
They are formed from the hot waters circulating in the
Earth’s crust through fractures. They are being
supersaturated when the minerals or rocks are
exposed in the waters for a long time.
Examples:
•
•
•
•
Malachite
Geodes
Petrified wood
Crocoite
Coal and Petroleum
Coal is a combustible rock mainly composed of carbon
along with variable quantities of other elements,
mostly hydrogen, sulfur, oxygen, and nitrogen.
Petroleum is a fossil fuel that naturally occurs in the
liquid form created by the decomposition of organic
matter beneath the surface of the earth millions of
Over time, the plants (mostly mosses) and algae were
buried and compressed under the weight of overlying
mud and vegetation. As the plant debris sifted deeper
under Earth’s surface, it encountered increased
temperatures and higher pressure. These areas of
buried plant matter are called peat bogs. Peat bogs
store massive amounts of carbon many meters
underground.
Under the right conditions, peat transforms into coal
through a process called carbonization.
How is Petroleum formed?
The geological conditions that would eventually create
petroleum formed millions of years ago, when plants,
algae, and plankton drifted in oceans and shallow seas.
These organisms sank to the seafloor at the end of
their life cycle. Over time, they were buried and
crushed under millions of tons of sediment and even
more layers of plant debris.
Deep under the basin floor, the organic material was
compressed between Earth’s mantle, with very high
temperatures, and millions of tons of rock and
sediment above. The organic matter began to
transform into a waxy substance called kerogen.
With more heat, time, and pressure, the kerogen
underwent a process called catagenesis and
transformed into hydrocarbons. Hydrocarbons are
simply chemicals made up of hydrogen and carbon
which result in coal, peat, and natural gas. these
natural gases and crude oil are then refined in oil
refineries thus, obtaining petroleum.
GUALINGCO, JEMINA P.
•An aggregate of mineral. They form major part of the Earth.
•It’s three major groups are: Igneous rocks, Sedimentary rocks, and
Metamorphic rocks.
2
ORIGIN OF IGNEOUS ROCKS
•Igneous rocks are any crystalline or glassy rocks that are formed from cooling and
solidification of magma.
•The igneous rocks can be held to derived from two kinds of magma, one granitic (acid)
and the other basaltic (basic), which originate different level below the Earth’s surface.
3
•It comes from great depth below the earth’s surface, it is mainly composed of O, Si, Al, Fe,
Na, Mg, Ca, and K.
4
5
Chemical composition
✘ ACID MAGMA – rich in Si, Na, and K
- poor in Ca, Mg, and Fe
✘ BASIC MAGMA – rich in Ca, Mg, and Fe
- poor in Si, Na, and K
○ BASIC MAGMA IS DIVIDED INTO THREE GROUPS
■ Ultra Basic Rock – this contains less than 45% of Si (ex: Periodite)
■ Basic Rock – this contain Si between 45% to 55%. (ex: Basalt)
6
■ Intermediate Rock – this contain Si between 55% to 65%. (ex: Diorite)
■ Acid Rock – this contains more than 65% of Si. (ex: Granite)
classification
1.
2.
3.
Over saturated – contains high amount of Si and
abundant quartz and Alkali Feldspars
Saturated – contains sufficient amount of Si and do not
contain quartz
Under saturated – contains less Si and high in Alkali and
aluminum oxides
7
TYPES OF IGNEOUS ROCKS
1.
2.
EXTRUSIVE ROCKS – any rock derived from magma
that was poured out or ejected at Earth’s surface
INTRUSIVE ROCKS – formed from magma that was
forced into older rocks at depth within Earth’s crust
8
Granite
✘ Granites usually have a coarse texture(individual
minerals are visible without magnification),
9
because the magma cools slowly underground, allowing
larger crystal growth.
✘ Granites are most easily characterized as light colored and
coarse grained as a result of cooling slowly below the
surface.
✘ Its three main minerals are feldspar, quartz, and mica, which
occur as silvery muscovite or dark biotite or both.
Granite
✘ Group- plutonic.
10
✘ Colour- variable but typically light-coloured.
✘ Texture- phaneritic (medium to coarse grained).
✘ Mineral content- orthoclase, plagioclase and quartz (generally more
orthoclase than plagioclase), often with smaller amounts of biotite,
muscovite or amphibole ( hornblende).
✘ Silica (SiO2) content -69%-77%.
✘ Uses- can be used as aggregate, fill etc. in the construction and roading
industries (often not ideal for concrete aggregate because of high silica
content); cut and polished for dimension stone for building facings, foyers
etc; cut and polished for bench tops and counters; cut and carved into
monuments, headstones, statues etc.
11
12
Chemical composition
A worldwide average of the chemical composition of granite, by weight percent,basedon 2485 analyses:
✘ SiO2 72.04% (silica)
✘ Al2O3 14.42% (alumina)
✘ K2O 4.12%
✘ Na2O 3.69%
✘ CaO 1.82%
✘ FeO 1.68%
✘ Fe2O3 1.22%
✘ MgO 0.71%
✘ TiO2 0.30%
✘ P2O5 0.12%
13
✘ MnO 0.05%
It always consists of the minerals quartz and feldspar, with or without a wide variety of other minerals
(accessory minerals). The quartz and feldspar generally give granite a light color, ranging from pinkish
to white.
Density + Melting Point
✘ The average density of it is between 2.65 and 2.75 g/cm3, its
compressive strength usually lies above 200 MPa, and its viscosity near
STP is 3–6 • 1019 Pa·s. Melting temperature is 1215–1260 °C. It has
poor primary permeability but strong secondary permeability.
14
TYPES OF IGNEOUS ROCKS
1.
2.
EXTRUSIVE ROCKS – any rock derived from magma
that was poured out or ejected at Earth’s surface
INTRUSIVE ROCKS – formed from magma that was
forced into older rocks at depth within Earth’s crust
15
SYENITE
✘ Syenite is intrusive igneous rock that basically composed of
an alkali feldspar and a ferromagnesian mineral.
16
✘ A unique group of alkali syenites is characterized by the
presence of a feldspathoid mineral inclusive of nepheline,
leucite, cancrinite, or sodalite (see nepheline syenite).
✘ Chemically, syenites comprise a slight amount of silica,
incredibly big amounts of alkalies, and alumina.
SYENITE
✘ Group- plutonic.
✘ Colour- variable but typically light coloured.
✘ Texture- phaneritic (medium to coarse grained).
17
✘ Mineral content- orthoclase, with lesser to minor plagioclase, minor mica,
augite, hornblende, magnetite etc.
✘ Silica (SiO2) content -60%-65%.
✘ Uses- dimension stone for building facings, foyers etc (often preferred to
granite due to its better fire-resistant qualities); can be used as
aggregate in the building and roading industries.
✘ New Zealand occurrences -Inland Kaikoura Range, Dunedin Volcano.
18
19
Chemical composition
✘ Syenite predominant mineral is alkaline charecter. Plagioclase feldspar may be present
small amaount less than 10%. Such feldspars often are interleaved as perthitic
components of the rock. if ferromagnesian minerals are present in syenite most of all, they
usually occur hornblende, amphibole and clinopyroxene. Biotite is rare. Other common
accessory minerals are apatite, titanite, zircon and opaques.
✘ Most syenites are either peralkaline with high proportions of alkali elements relative to
aluminum, or peraluminous with a higher concentration of aluminum relative to alkali
and earth-alkali elements (predominantly K, Na, Ca).
Thank you for listening!
20
Jonard A. Maallo
BSCE-2A
April 03, 2021
GEO-C
IGNEOUS ROCKS
GABBRO
Minerals
Essential minerals are a plagioclase (generally labradorite) and a monoclinic
pyroxene (augite or diallage). The plagioclase composition reflects the high CaO and
low Na2O content in gabbro (see analysis, p. 100). Other minerals which may be
present in different gabbros are hypersthene, olivine, hornblende, biotite, and
sometimes nepheline. Ilmenite, magnetite, and apatite are common accessories.
Texture
Coarsely crystalline, rarely porphyritic, sometimes with finer modifications. Hand
specimens appear mottled dark grey to greenish-black in colour because of the large
mafic content. Under the microscope the texture appears as interlocking crystals (Fig.
5.19).
Varieties
● Norite is a variety containing essentially hypersthene instead of augite, i.e. a
hypersthene-labradorite rock, and is of common occurrence.
● Troctolite has olivine and plagioclase (no augite)
● Quartz-gabbro contains a little interstitial quartz, derived from the last liquid to
crystallize from a magma with slightly higher silica content than normal
DIORITE
Diorite is related to granite, and by increase of silica content and the incoming of
orthoclase grades into the acid rocks,
thus: diorite -> quartz diorite -> granodiorite -> granite.
Minerals
Plagioclase (andesine) and hornblende; a small amount of biotite or pyroxene,
and a little quartz may be present, and occasional orthoclase. Accessories include
Fe-oxides, apatite and sphene. The dark minerals make up from 15% to 40% of the rock,
and hand specimens are less dark than gabbro.
Texture
Coarse to medium-grained, rarely porphyritic. In hand specimens’ minerals can
usually be distinguished with the aid of a lens. Under the microscope minerals show
interlocking outlines, the mafic minerals tending to be idiomorphic (=exhibit a regular
shape).
Varieties
●
●
Quartz-diorite (the amount of quartz is much less than in granite) is
perhaps more common than diorite as defined above.
Fine-grained varieties are called microdiorite.
PEGMATITES
Pegmatites are very coarse-grained vein rocks that represent the last part of a
granitic magma to solidify. The residual magmatic fluids are rich in volatile constituents,
which contain the rarer elements in the magma. Thus in addition to the common
minerals quartz, alkali feldspar and micas, large crystals of less common minerals such
as beryl, topaz, and tourmaline are found in pegmatities. Also residual fluids carrying
other rare elements, e.g. lithium, cerium, tungsten, give minerals in the pegmatites that
can be worked for their extraction, such as the lithium pyroxene spodumene, the cerium
phosphate monazite and wolfram. The mica used in industry - mainly muscovite and
phlogopite (q.v), is obtained from pegmatites; individual crystals may be many
centimetres across, yielding large mica plates. Canada, India, and the United States
produce mica from such sources. Pegmatites are found in the outer parts of intrusive
granites and also penetrating the country-rocks.
Drewberry C. Intal
BSCE-2A
April 08, 2021
WRITTEN REPORT
CLASSIFICATION OF ROCKS: METAMORPHIC
Introduction:
Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while
buried deep below Earth's surface. Exposure to these extreme conditions has altered the
mineralogy, texture, and chemical composition of the rocks. Metamorphic rocks arise from the
transformation of existing rock to new types of rock, in a process called metamorphism. The
original rock (protolith) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F)
and, often, elevated pressure (100 megapascals (1,000 bar) or more), causing profound physical or
chemical changes. During this process, the rock remains mostly in the solid state, but gradually
recrystallizes to a new texture or mineral composition. The protolith may be a sedimentary,
igneous, or existing metamorphic rock.
Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land
surface. They are classified by their protolith, their chemical and mineral makeup, and their texture.
They may be formed simply by being deeply buried beneath the Earth's surface, where they are
subject to high temperatures and the great pressure of the rock layers above. They can also form
from tectonic processes such as continental collisions, which cause horizontal pressure, friction,
and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of
hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now
exposed at the Earth's surface following erosion and uplift) provides information about the
temperatures and pressures that occur at great depths within the Earth's crust.
Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite. Slate and
quartzite tiles are used in building construction. Marble is also prized for building construction and
as a medium for sculpture. On the other hand, schist bedrock can pose a challenge for civil
engineering because of its pronounced planes of weakness.
Metamorphic Minerals
Because every mineral is stable only within certain limits, the presence of certain minerals in
metamorphic rocks indicates the approximate temperatures and pressures at which the rock
underwent metamorphosis. These minerals are known as index minerals. Examples include
sillimanite, kyanite, staurolite, andalusite, and some garnet.
Other minerals, such as olivines, pyroxenes, hornblende, micas, feldspars, and quartz, may be
found in metamorphic rocks, but are not necessarily the result of the process of metamorphism.
These minerals can also form during the crystallization of igneous rocks. They are stable at high
temperatures and pressures and may remain chemically unchanged during the metamorphic
process.
Texture
Metamorphic rocks are typically more coarsely crystalline than the protolith from which they
formed. Atoms in the interior of a crystal are surrounded by a stable arrangement of neighboring
atoms. This is partially missing at the surface of the crystal, producing a surface energy that makes
the surface thermodynamically unstable. Recrystallization to coarser crystals reduces the surface
area and so minimizes the surface energy.
Although grain coarsening is a common result of metamorphism, rock that is intensely deformed
may eliminate strain energy by recrystallizing as a fine-grained rock called mylonite. Certain kinds
of rock, such as those rich in quartz, carbonate minerals, or olivine, are particularly prone to form
mylonites, while feldspar and garnet are resistant to mylonitization.
Foliation
Many kinds of metamorphic rocks show a distinctive layering called foliation (derived from the
Latin word folia, meaning "leaves"). Foliation develops when a rock is being shortened along one
axis during recrystallization. This causes crystals of platy minerals, such as mica and chlorite, to
become rotated such that their short axes are parallel to the direction of shortening. This results in
a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them.
Foliated rock often develops planes of cleavage. Slate is an example of a foliated metamorphic
rock, originating from shale, and it typically shows well-developed cleavage that allows slate to
be split into thin plates.
The type of foliation that develops depends on the metamorphic grade. For instance, starting with
a mudstone, the following sequence develops with increasing temperature: The mudstone is first
converted to slate, which is a very fine-grained, foliated metamorphic rock, characteristic of very
low-grade metamorphism. Slate in turn is converted to phyllite, which is fine-grained and found
in areas of low-grade metamorphism. Schist is medium to coarse-grained and found in areas of
medium grade metamorphism. High-grade metamorphism transforms the rock to gneiss, which is
coarse to very coarse-grained.
Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with
distinctive growth habits, will not be foliated. Marble lacks platy minerals and is generally not
foliated, which allows its use as a material for sculpture and architecture.
Classification
Metamorphic rocks are one of the three great divisions of all rock types, and so there is a great
variety of metamorphic rock types. In general, if the protolith of a metamorphic rock can be
determined, the rock is described by adding the prefix meta- to the protolith rock name. For
example, if the protolith is known to be basalt, the rock will be described as a metabasaltic.
Likewise, a metamorphic rock whose protolith is known to be a conglomerate will be described as
a metaconglomerate. For a metamorphic rock to be classified in this manner, the protolith should
be identifiable from the characteristics of the metamorphic rock itself, and not inferred from other
information.
Under the British Geological Society classification system, if all that can be determined about the
protolith is its general type, such as sedimentary or volcanic, the classification is based on the
mineral mode (the volume percentages of different minerals in the rock). Metasedimentary rocks
are divided into carbonate-rich rock (metacarbonates or calcsilicate-rocks) or carbonate-poor
rocks, and the latter are further classified by the relative abundance of mica in their composition.
This ranges from low-mica psammite through semipellite to high-mica pellite. Psammites
composed mostly of quartz are classified as quartzite. Metaigneous rocks are classified similarly
to igneous rocks, by silica content, from meta-ultramafic-rock (which is very low in silica) to
metafelsic-rock (with a high silica content).
Hazards
Schistose bedrock can pose a challenge for civil engineering because of its pronounced planes of
weakness. A hazard may exist even in undisturbed terrain. On August 17, 1959, a magnitude 7.2
earthquake destabilized a mountain slope near Hebgen Lake, Montana, composed of schist. This
caused a massive landslide that killed 26 people camping in the area.
Metamorphosed ultramafic rock contains serpentine group minerals, which includes varieties of
asbestos that pose a hazard to human health.
References:
https://en.wikipedia.org/wiki/Metamorphic_rock
https://geology.com/rocks/metamorphic-rocks.shtml
https://www.usgs.gov/faqs/what-are-metamorphic-rocks-0?qt-news_science_products=0#qtnews_science_products
https://www.nationalgeographic.org/encyclopedia/metamorphic-rocks/
LABARDA, JOHN ERNEST T.
GEO
APRIL 7, 2021
GEOLOGY REPORT
CLASSIFICATION OF ROCKS: IGNEOUS & SEDIMENTARY
ROCKS
•
It is aggregate of mineral. They form a major part of the earth’s crust
Rocks are divided into three major groups:
1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks
IGNEOUS ROCKS
Igneous rocks are formed by cooling and solidification of magma.
Magma is hot, viscous, siliceous, melts, contains water vapor, and gases. It comes from great
depth below the earth’s surface.
It is mainly composed of O, Si, Al, Fe, Na, Mg, Ca, and K.
• General characteristics of magma:
• Parent material of igneous rocks
• Forms from partial melting of rocks
• Magma at surface is called lava
CHEMICAL COMPOSITION OF IGNEOUS ROCKS
•
Acid Magma – is rich in Si, Na, & K. Poor in Ca, Mg, & Fe.
•
Basic Magma – is rich in Ca, Mg, & Fe. Poor in Si, Na, & K.
CLASSIFICATION OF IGNEOUS ROCKS
Over saturated
- contains high amount of Si & abundant quartz with alkali feldspars
Saturated
- contains sufficient amount of Si with no quartz.
Under saturated
- contains less Si & high in alkali with aluminum oxides.
IGNEOUS ROCKS TEXTURES
Texture refers to the size, shape and arrangement of minerals’ grains and is an important
characteristic of igneous rocks.
Grain size records cooling history. It all comes down to the rate at which the rock cools. Other
factors include the diffusion rate, which is how atoms and molecules move through the liquid.
LABARDA, JOHN ERNEST T.
GEO
APRIL 7, 2021
The rate of crystal growth is another factor, and that's how quickly new constituents come to the
surface of the growing crystal. New crystal nucleation rates, which is how enough chemical
components can come together without dissolving, is another factor affecting the texture.
DIFFERENT TEXTURES OF IGNEOUS ROCKS
1. Aphanitic Texture
- An aphanitic texture consists of an aggregate of very small mineral grains, too small
to be seen clearly with the naked eye. Aphanitic textures record rapid cooling at or
very near Earth’s surface and are characteristic of extrusive (volcanic) igneous rock.
2. Phaneritic Texture
- A phaneritic texture consists of an aggregate of large mineral grains, easily visible
without magnification . Phaneritic textures record slow cooling within Earth and are
characteristic of intrusive (plutonic) igneous rocks.
3. Glassy Texture
- Very rapid cooling of lava produces a “glassy texture”. The lava cools so quickly
that atoms do not have time to arrange in an ordered three dimensional network
typical of minerals. The result is natural glass, or obsidian.
4. Vesicular Texture
- Gases trapped in cooling lava can result in numerous small cavities, vesicles, in the
solidified rock.
5. Pyroclastic Texture
- Igneous rocks formed of mineral and rock fragments ejected from volcanoes by
explosive eruptions have pyroclastic textures. The ejected ash and other debris
eventually settles to the surface where it is consolidated to form a Pyroclastic
igneous rock. Much of this material consists of angular pieces of volcanic glass
measuring up to 2mm.
6. Porphyritic Texture
- Igneous rocks comprised of minerals of two or more markedly different grain sizes
have a porphyritic texture. The coarser grains are called phenocrysts and the smaller
grains groundmass. Porphyritic textures result from changes in cooling rate and
include both aphanitic porphyrys and phaneritic porphyrys.
FORMS OF IGNEOUS BODIES
1. Extrusive Igneous Bodies
- Volcanic (extrusive) igneous rocks form by cooling and crystallization of lava or by
consolidation of pyroclastic material, such as volcanic ash, ejected from volcanoes.
2. Intrusive Igneous Bodies
- Plutonic (intrusive) igneous rocks form as magma cools and crystallizes within Earth.
LABARDA, JOHN ERNEST T.
GEO
APRIL 7, 2021
It is not possible to study magma directly. However, studying lavas can tell us a lot.
• Magmas have a range of compositions
• Characterized by high temperatures
• Have the ability to flow
SEDIMENTARY ROCKS
Sedimentary rocks are the type of rocks that are formed by the deposition of material at earth's
surface and within the bodies of rocks.
-
Contributes about 8% of total volume of crust.
Sedimentary rocks are those which have formed out of sediments.
The study of sedimentary rocks and rock strata provides information about the
subsurface that is useful for civil engineering.
Sediments are rock fragments which are product of weathering.
Weathering has already been defined as natural processes of disintegration and
decomposition of rocks.
Sediments, which have formed out of disintegration, are loose materials of various
sizes like clay, sand, and pebbles.
FORMATION OF SEDIMENTARY ROCKS
Sedimentary rocks are formed at, or near the Earth’s surface by accumulation and lithification of
fragments of pre-existing rocks or by precipitation from solution at normal surface temperatures.
On the basis of their mode of formation, sedimentary rocks are classified as:
1. Clastic sedimentary rocks
2. Bioclastic sedimentary rocks
3. Crystalline sedimentary rocks
1. Clastic Sedimentary Rocks
- Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks.
Pieces of rock are loosened by weathering, then transported to some basin or
depression where sediment is trapped. If the sediment is buried deeply, it becomes
compacted and cemented, forming sedimentary rock
2. Bioclastic Sedimentary Rocks
- Such as coal, and some limestones are formed from the accumulation of plant or
animal debris.
- Organic sedimentary rocks are those containing large quantities
of organic molecules. Organic molecules contain carbon, but in this context we are
referring specifically to molecules with carbon-hydrogen bonds, such as materials
from the soft tissues of plants
3. Crystalline Sedimentary Rocks
- are formed when dissolved materials precipitate from solutions.
LABARDA, JOHN ERNEST T.
GEO
APRIL 7, 2021
DISTINCTION BETWEEN IGNEOUS & SEDIMENTARY ROCKS
IGNEOUS ROCKS:
-
-
Igneous rocks form when molten rock (magma or lava) cools, crystallizes, and
solidifies.
Metamorphic rocks form from heat and pressure.
Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earth's
crust by volume.
Igneous rocks form at temperatures and pressures that destroys fossil remnants.
The structures of igneous rocks are large scale features, which are dependent on
several factors like:
o Composition of magma.
o Viscosity of magma.
o Temperature and pressure at which cooling and consolidation takes place.
o Presence of gases and other volatiles.
Igneous rocks are classified according to mode of occurrence, texture, mineralogy,
chemical composition, and the geometry of the igneous body
SEDIMENTARY ROCKS:
-
-
-
Sedimentary rocks originate when particles settle out of water or air, or by
precipitation of minerals from water. They accumulate in layers.
Sedimentary rocks are formed from pressure, compaction and cementation.
The sedimentary rock cover of the continents of the Earth's crust is extensive, but
the total contribution of sedimentary rocks is estimated to be only 8% of the total
volume of the crust.
Fossils are most commonly found in sedimentary rock.
Structures in sedimentary rocks can be divided into 'primary' structures (formed
during deposition) and 'secondary' structures (formed after deposition). Structures
are always large-scale features that can easily be studied in the field.
Based on the processes responsible for their formation, sedimentary rocks can be
subdivided into three groups: clastic sedimentary rocks, bioclastic sedimentary rocks,
and crystalline sedimentary rocks
JOHN DARLY J. MANANSALA
BSCE-2A
DOLERITE & BASALT
(PETROLOGY)
Dolerite
The chemistry of this intrusive rock
corresponds to gabbro but its texture is finer.
Dolerite forms dykes, sills, and other
intrusions. The rock is dark grey in color,
except where its content of feldspar is
greater than average. Dolerite is important
as a road-stone for surfacing because of its
toughness, and its capacity for holding a
coating of bitumen and giving a good 'bind'.
In its un-weathered state dolerite is one of
the strongest of the building stones and used
for vaults and strong-rooms, as in the Bank
of England.
Minerals
plagioclase, pyroxene, hornblende and
quartz.
Texture
Medium to fine-grained; some dolerites
have a coarser texture, when the lath-like
shape of the feldspar is less emphatic and
the rock tends towards a gabbro. When the
plagioclase 'laths' are partly or completely
enclosed in augite the texture is called
ophitic; this interlocking of the chief
components gives a very strong, tough rock.
Varieties
Normal dolerite = labradorite + augite •+•
iron oxides; if olivine is present the term
olivine-dolerite is used. Much altered
dolerites, in which both the feldspars and
mafic minerals show alteration products are
called diabase, though in America the term
is often used synonymously with the British
usage of dolerite.
Basalt
Basalt is a dark, dense-looking rock, often
with small porphyritic crystals, and
weathering to a brown colour on exposed
surfaces. It is the commonest of all lavas, the
basalt flows of the world being estimated to
have five times the volume of all other
extrusive rocks together. Basalt also forms
small intrusions in form of dyke and/or thin
sill.
Minerals
Essentially plagioclase (labradorite) and
augite; but some basalts have a more calcic
plagioclase. Olivine occurs in many basalts
and may show alteration to serpentine.
Magnetite and ilmenite are common
accessories; if vesicles are present they may
be filled with calcite, chlorite, chalcedony,
and other secondary minerals. Nepheline,
leucite, and analcite are found in basalts
with a low content of silica.
Texture
Fine-grained or partly glassy; hand
specimens appear even-textured on broken,
unless the rock is porphyritic or vesicular;
small porphyritic crystals of olivine or
augite may need some magnification for
identification. Under the microscope the
texture
is
microcrystalline
to
cryptocrystalline or partly glassy. At the
chilled margins of small intrusions a
selvedge of black basalt glass, or tachylite,
is formed by the rapid cooling.
Varieties
Basalt and olivine-basalt are abundant;
varieties containing feldspathoids include
nepheline-basalt
and leucite-basalt (e.g. the lavas from
Vesuvius). Soda-rich basalts in which the
plagioclase is mainly albite
are called spilites, and often show
'pillow-structure' in the mass, resembling a
pile of sacks; they are erupted on the sea
floor. Their rapid cooling in the sea prevents
the minerals crystallized from achieving
chemical equilibrium; they are reactive and
alter readily. Between the pillows are baked
marine sediments, often containing chert and
jasper (SiO2). These features of pillow lavas
make them a most unsuitable form of basalt
for concrete aggregate.
Some of the great flows of basalt in different
parts of the world have been referred to
earlier; their virtually constant composition
suggests a common source, the basaltic layer
of the Earth’s crust.