Rocks: Materials of the Solid Earth
Prepared by :
Ms Stefany May P. Indico
IV-BEEd
Earth and its Environment
Rocks: Materials of the Solid Earth
This report contains
the following information:
1. Geologists: 'We May Be Slowly Running Out Of
Rocks'
2. The rock Cycle
a. Crystallization
b. Weathering
c. Lithification
3. Classes of rocks:
a. Igneous Rocks
b. Sedimentary Rocks
c. Metamorphic Rocks
4. Resources from Rock
5. References
Earth and its Environment
Rocks: Materials of the Solid Earth
Geologists: 'We May Be Slowly Running Out Of
Rocks'
MAY 1, 2010
RALEIGH, NC—A coalition of geologists are challenging the way we look at global
stone reserves, claiming that, unless smarter methods of preservation are
developed, mankind will eventually run out of rocks.
"If we do not stop using them up at our current rate, rocks as we know them will be
a thing of the past," renowned geologist Henry Kaiser said at a press conference
Tuesday. "Igneous, metamorphic, even sedimentary: all of them could be gone in
as little as 500,000 years."
"Think about it," Kaiser added. "When was the last time you even saw a boulder?"
The scientists warned that, although people have long considered the world's rock
supply to be inexhaustible, it has not created a significant number of new rocks
since the planet cooled some 3.5 billion years ago. Moreover, the earth's rocks
have been very slowly depleting in the last century due to growing demand for
fireplace mantels, rock gardens, gravel, and paperweights.
Kaiser claims that humanity has "wreaked havoc" on the earth's stones by picking
them up, carrying them around, and displacing them from their natural habitat.
"A rock can take millions of years to form, but it only takes a second for someone to
skip a smooth pebble into a lake, and then it is gone." Dr. Kaiser said. "Perhaps
these thoughtless rock-skippers don't care if they leave our planet completely
devoid of rocks, but what about our children? Don't they deserve the chance to
hold a rock and toss it up and down a few times?"
Continued Kaiser, "We are on a collision course to a world without rocks."
Geologist Victoria Merrill, who has been at the forefront of the rock conservation
battle since 2004, said there are simple steps people can take to reduce their rock
consumption.
"Only take as many rocks as you absolutely need," said Dr. Merrill, author of the
book No Stone Unturned: Methods For Modern Rock Conservation. "And once you
are finished with your rocks, do not simply huck them into the woods. Place the rock
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Rocks: Materials of the Solid Earth
down gently where you found it so that others may look at the rock and enjoy it for
years to come."
Merrill went on to point out that, even if there were some "magic hole" in the earth's
crust that could miraculously spew out rocks every 10 years or so, modern society's
obsession with rocks means that we would still run out of them far more quickly than
they could be replenished.
"Just look at the pet rock craze: In 10 years, millions upon millions of rocks were
painted, played with, and discarded like trash," Merrill said. "Looking back,
mankind's arrogance and hubris is startling."
But critics of the movement have already begun to surface, claiming that Kaiser
and his colleagues are simply preying on people's fears of losing rocks.
While acknowledging that we should reduce our dependence on foreign rocks,
many have argued that the current rock supply could easily last for the next 2
million years, by which time technology will have advanced enough to allow for
the production of endless quantities of cheap, durable basalt.
Others who oppose the rock-loss theory claim that rocks were put on the earth to
be used by humans in marble statues or kitchen countertops as they see fit.
"Take the Rocky Mountains, for example: There's plenty of rocks right there,"
Colorado resident Kyle Peters said. "It's our right as Americans to use as many rocks
as we need for whatever purposes we decide, and no scientist is going to scare me
into thinking otherwise."
"This country was built on rocks," he added. "Remember that."
Rock Cycle
The Rock Cycle views many of the interrelationships among different parts of
the earth. It helps us understand the origin of igneous, sedimentary and
metamorphic rocks. It is a group of changes. Igneous rock can change into
sedimentary rock or into metamorphic rock. Sedimentary rock can change into
metamorphic rock or into igneous rock. Metamorphic rock can change into
igneous or sedimentary rock.
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Rocks: Materials of the Solid Earth
Igneous rock forms when magma cools and makes crystals. Magma is a hot
liquid made of melted minerals form inside the earth. The minerals can form crystals
when they cool. Igneous rock can form underground, where the magma cools and
solidifies slowly. Or, igneous rock (ignis-fire) can form above ground, where the
magma cools quickly. And this process is called Crystallization.
Igneous rocks are exposed to the surface, and they will undergo weatheringis the breaking down of rocks, soils and minerals as well as artificial materials
through contact with the Earth's atmosphere, biota and waters. On Earth's surface,
wind and water can break rock into pieces. They can also carry rock pieces to
another place. Usually, the rock pieces, called sediments, drop from the wind or
water to make a layer. The layer can be buried under other layers of sediments.
Next, the sediments undergo lithification, a term meaning “conversion into
rock”. After a long time the sediments can be cemented together to make
sedimentary rock. In this way, igneous rock can become sedimentary rock.
If the resulting sedimentary rock is buried deep within earth and involved in
the dynamics of mountain building or intruded by mass of magma, it will be
subjected to great pressure or intense heat. The sedimentary rock will react to the
changing environment and turn into the third type, metamorphic rock. When
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Rocks: Materials of the Solid Earth
metamorphic rock is subjected to additional pressure changes or to still higher
temperatures, it will melt, creating magma, which eventually crystallizes into
igneous rock.
Processes driven by heat from earth’s interior are responsible for creating
igneous and metamorphic rocks. Weathering and erosion, external processes
powered by energy from the sun, produce the sediments from which sedimentary
rocks form. And this rock cycle never stop.
Classes of Rocks
Rocks are generally classified by mineral and chemical composition, by
the texture of the constituent particles and by the processes that formed them.
These indicators separate rocks into igneous, sedimentary, and metamorphic. They
are further classified according to particle size. The transformation of one rock type
to another is described by the geological model called the rock cycle.
Igneous rocks are formed when molten magma cools and are divided into
two main categories: plutonic and volcanic. Plutonic or intrusive rocks result when
magma cools and crystallizes slowly within the Earth's crust (example granite), while
volcanic or extrusive rocks result from magma reaching the surface either as lava or
fragmental eject (examples pumice and basalt)
Sedimentary rocks are formed by deposition of either clastic sediments,
organic matter, or chemical precipitates (evaporates), followed by compaction of
the particulate matter and cementation during diagenesis. Sedimentary rocks form
at
or
near
the
Earth's
surface.
Mud
rocks
comprise
65%
(mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to
15% (limestoneand dolostone).
Metamorphic rocks are formed by subjecting any rock type (including
previously
formed
metamorphic
rock)
to
different temperature and
pressure conditions than those in which the original rock was formed. These
temperatures and pressures are always higher than those at the Earth's surface and
must be sufficiently high so as to change the original minerals into other mineral
types or else into other forms of the same minerals (e.g. by recrystallisation).
The three classes of rocks — the igneous, the sedimentary and the
metamorphic — are subdivided into many groups. There are, however, no hard
and fast boundaries between allied rocks. By increase or decrease in the
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Rocks: Materials of the Solid Earth
proportions of their constituent minerals they pass by every gradation into one
another, the distinctive structures also of one kind of rock may often be traced
gradually merging into those of another. Hence the definitions adopted in
establishing rock nomenclature merely correspond to selected points (more or less
arbitrary) in a continuously graduated series.
Igneous Rocks: “Formed by Fire”
Igneous
rock (derived
from
the Latin word
meaning
of
fire,
from ignis meaning fire) is one of the three main rock types, the others
being sedimentary and metamorphic rock. Igneous rock is formed through the
cooling and solidification of magma or lava. Igneous rock may form with or
without crystallization, either below the surface as intrusive (plutonic) rocks or on the
surface as extrusive (volcanic) rocks. The rocks that result when lava solidifies are
classified as volcanic or extrusive, because they are extruded onto the surface. The
magma not able to reach the surface eventually crystallizes at depth. Igneous
rocks produced in this manner are termed plutonic, or intrusive, because they
intruded existing rocks.
Intrusive igneous rocks
Close-up of granite (an intrusive igneous rock)
exposed in Chennai, India.
Extrusive igneous rocks
Basalt (an extrusive igneous rock in this case);
light coloured tracks show the direction of lava
flow
Classifying Igneous Rocks
Igneous rocks can be classified based on their texture and mineral
constituents.
Texture
Describe the overall appearance of an igneous rocks based on their
size, shape, and arrangement. Igneous rocks could be fine-grained texture,
coarse grained texture, porphyritic texture, and glassy texture. An igneous
rocks that form rapidly at the surface or as small masses within the upper
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Rocks: Materials of the Solid Earth
crust have a fine-grained texture, with the individual crystals too small to be
seen with the unaided eye. When large masses of magma solidify far below
the surface, they form igneous rocks that exhibit a coarse-grained texture.
These coarse-grain rocks have the appearance of a mass of intergrown
crystals, which are roughly equal in size and large enough that the individual
minerals can be identified with the unaided eye. When the magma that
already contains some large crystals suddenly erupts at the surface, the
remaining molten portion of the lava would cool quickly the resulting rock,
which has large crystals embedded in a matrix of smaller crystals, is said to
have a porphyritic texture. During some volcanic eruptions, molten rock is
ejected into the atmosphere, where it is quenched very quickly. Rapid
cooling of this type may generate with a glassy texture.
Mineral Composition
The mineral make-up of an igneous rock depends on the chemical
composition of the magma from which it crystallize. N>I. Bowen discovered
that as magma cools in laboratory, certain minerals crystallize first, at very
high temperature. At successively lower temperature, other minerals
crystallize.
Bowen also demonstrated that if mineral remains in the molten solution
after crystallization, it will react with the sequence shown in the figure below.
For this reason, this arrangement of minerals became known as Bowen’s
reaction series.
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Rocks: Materials of the Solid Earth
Sedimentary Rocks: “Compacted and Cemented Sediment”
Sedimentary rock is a type of rock that is formed by sedimentation of
material at the Earth's surface and within bodies of water. Sedimentation is the
collective name for processes that cause mineral and/or organic particles (detritus)
to settle and accumulate or minerals to precipitate from a solution. Particles that
form a sedimentary rock by accumulating are called sediment. Before being
deposited, sediment was formed by weathering and erosion in a source area, and
then transported to the place of deposition by water, wind, mass movement or
glaciers which are called agents of denudation.
Classifying sedimentary rocks
Materials accumulating as sediment have two principal sources. First,
sediments may originate as solid particles from weathered rocks, such as the
igneous rocks. These particles are called detritus, and the sedimentary rocks
that they form are called detrital sedimentary rocks.
The second major source of sediment is soluble materials produces
largely by chemical weathering. When they dissolved substances are
precipitated back as solids, they are called chemical sediments, and they
form chemical sedimentary rocks.
Metamorphic Rocks: New Rock from Old
Metamorphic rock is the transformation of an existing rock type, the protolith,
in a process called metamorphism, which means "change in form". The protolith is
subjected to heat and pressure (temperatures greater than 150 to 200 °C and
pressures of 1500 bars[1]) causing profound physical and/or chemical change. The
protolith may be sedimentary rock, igneous rock or another older metamorphic
rock. Metamorphic rocks make up a large part of the Earth's crust and are
classified by texture and by chemical and mineral assemblage (metamorphic
facies). They may be formed simply by being deep beneath the Earth's surface,
subjected to high temperatures and the great pressure of the rock layers above it.
They can form from tectonic processes such as continental collisions, which cause
horizontal pressure, friction and distortion. They are also formed when rock is heated
up 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
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Rocks: Materials of the Solid Earth
at great depths within the Earth's crust. Some examples of metamorphic rocks
are gneiss, slate, marble, schist, and quartzite.
Metarmorphism is the transformation of one rock type into another.
Metamorphic rocks are produced from preexisting igneous, sedimentary and
metamorphic rocks. Metamorphism occurs in one of two settings: 1. when rock is
intruded by magma body, contact or thermal metamorphism may take place.
Here, change is driven by a rise in temperature within the host rock surrounding a
molten igneous body; 2. During mountain building great quantities of rock are
subjected to directed pressures and high temperature associated with large-scale
deformation called regional metamorphism.
Three Classes of Rocks
Class and Origin
Igneous
From the hot, molten
magma which either
comes to the surface as
lava, or is cooled and
solidified within the crust.
The rate of cooling and the
mineral content of the
magma determine the
kind of igneous rock.
Rocks with visible mineral
crystals result from slow
cooling. The faster the
magma cools, the smaller
are the crystals.
Texture
Large crystals
Small crystals
Large and
very small
crystals
Very small
crystals
Glassy
Common Types
PEGMATITE originates deep
in the crust, forming very
large crystals due to slow
cooling.
GRANITE results from slow
cooling and consists of
crystals of quartz, mica,
feldspar, and hornblende
which are easily visible.
PORPHYRY is formed from
magma that cooled deep
in the crust first and then
moved nearer the surface.
Large crystals are set in a
background of very small
crystals.
BASALT is a dark, dense
rock. Crystals are
microscopic in size, which
tells us that this rock once
flowed near or on the
surface or the earth.
OBSIDIAN is commonly
called volcanic glass. It
cooled so quickly, it has no
crystals.
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Rocks: Materials of the Solid Earth
Fragmental
Sedimentary
Rocks are broken up into
small particles by
weathering and erosion.
These materials, or
sediments, are carried by
streams and deposited in
the oceans in layers.
Eventually these layers are
buried by more sediments
and compressed into rock.
Some sedimentary rock is
made of tiny particles that
settle out of sea water
onto the ocean floor, and
some is made from the
actual remains of plants
and animals.
Coarse and
fine particles
Medium
coarse
particles
Fine particles
Fine particles
Fragmental to
compact
Crystalline
Metamorphic
Metamorphic means
change of form. When
rocks are subjected to
sufficient heat, pressure, or
movement (like faulting),
there is a recooking of
minerals within the rocks
and the minerals are
rearranged, in some cases
in distinct bands.
Coarse
banding
Thin banding
Very fine
banding
Compact
PUMICE is very light, is full of
holes, and floats in water.
Its origin is volcanic.
CONGLOMERATE consists
of pebbles and finer
material. It resembles
concrete.
SANDSTONE is made of
sand particles, principally
quartz.
SHALE, the most common
sedimentary rock, is made
of visible layers of silt and
clay.
LIMESTONE can be made
up of tiny particles of
calcium carbonate that
settled to the ocean floor,
or it can be entirely made
of shells or coral.
PEAT is the compressed
remains of plants.
Compressed further, it
forms lignite, then
bituminous coal.
GYPSUM results from
evaporation of water from
ancient seas.
GNEISS was once granite
or conglomerate. It has
dark and light minerals in
wide bands.
SCHIST may have originally
been shale, slate, granite,
basalt, sandstone, or
limestone. It is usually rich in
mica.
SLATE, once shale, breaks
easily into layers.
QUARTZITE was originally
sandstone.
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Rocks: Materials of the Solid Earth
Compact
Crystalline
ANTHRACITE, or hard coal,
was originally bituminous
coal.
MARBLE was once
limestone.
Resources from Rocks and Minerals
The outer layer of Earth, which we call the crust, is only as thick when
compared to the remainder of the Earth as a peach skin is to a peach, yet it is of
supreme importance to us. We depend on it for fossil fuels and as a source of such
diverse minerals as the talc for baby powder, salt to flavor food and gold for world
trade. In fact, on occasion, the availability or absence of a certain Earth material s
requirement of modern society grow, the need to locate additional supplies of
useful minerals also grows and becomes more challenging.
Metallic Mineral Resources
Some of the most important accumulation of minerals such as gold,
silver, copper, mercury, lead, platinum, and nickel, are produced by igneous
and metamorphic processes.
Ore minerals of important metals
metals
Ore Mineral
Aluminum
Bauxite
Chromium
Chromite
Copper
Bornite
Chalcocite
Gold
Native Gold
iron
Hematite
Magnetite
limonite
Among the best-known and most important ore deposit are those
generated from hydrothermal solution. Included in this group are gold,
deposits. Some of the fluids move along fractures or bedding plates, where it
cools and precipitates the metallic ions to produce vein deposits. Many of
the most deposits of gold, silver, and mercury. Another important type of
hydrothermal activity is called disseminated deposit. Rather than being
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Rocks: Materials of the Solid Earth
concentrated in narrow veins and dikes, these ores are distributed as minute
masses throughout the entire rock mass.
Non-metallic Mineral Resources
Mineral resources not used for fuels or processes for the metals they
contain are referred to as nonmetallic mineral resources. These materials are
extracted and processed either to make use of the nonmetallic elements
they contain or for the physical or chemical properties they posses. Non
metallic minerals are commonly divided into two broad groups: building
materials and industrial materials.
References:
http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html
http://www.windows2universe.org/earth/geology/rock_cycle.html
http://www.robinsonlibrary.com/science/geology/petrology/classes.htm
http://en.wikipedia.org/wiki/Rock_(geology)
http://www.theonion.com/articles/geologists-we-may-be-slowly-running-out-ofrocks,17341/
Earth and its Environment