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Lecture # 3
Geological Cycle Rock Formation
and Types of Rocks
Instructor:
Dr. Attaullah Shah
Department of Civil Engineering
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City University of Science and IT Peshawar
Outlines of the Presentation
1. Geological Cycle: Rock formation
2. Types of Rocks
3. Major rocks and their use in Civil Engineering
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The Geological Cycle: Rock formation
Geological
cycle
includes
many
processes
acting
simultaneously. The most important of these begin with molten
magma from within the earth forming into rock, then continue
with rocks being broken down into soil, and that soil being
converted back into rock. It is sometimes called as Rock cycle
as well.
The rock cycle is a fundamental concept in geology that
describes the dynamic transitions through geologic time among
the three main rock types:
• Sedimentary,
• Metamorphic, and
• Igneous.
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The Geological Cycle: Rock formation
Rocks are classified according to their place in the geologic cycle.
The three major categories are:
1.Igneous,
2.Sedimentary and
3.Metamorphic
A
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2
3
4
5
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diagram of the rock cycle. Legend:
= magma;
= crystallization (freezing of rock);
= igneous rocks;
= erosion;
= sedimentation;
= sediments & sedimentary rocks;
= tectonic burial & metamorphism;
= metamorphic rocks;
= melting.
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Types of Rocks
Igneous Rock: Igneous rock (derived from the Latin word
"Igneus" meaning of fire, from "Ignis" meaning fire) is one of
the three main rock types (the others being sedimentary and
metamorphic rock).
The geologic cycle begins with magma, a molten rock deep inside the
earth. This magma cools as it moves upward toward the ground
surface, forming igneous rocks.
When rocks are pushed deep under the Earth's surface, they may melt
into magma. If the conditions no longer exist for the magma to stay in
its liquid state, it will cool and solidify into an igneous rock.
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Qualities of magma
 Natural magmas are hot, viscous siliceous melts in which the chief
elements present are silicon and oxygen, and the metals potassium,
sodium, calcium, magnesium, aluminum, and iron (in the order of
their chemical activity).
• Many other elements, and gases such as CO2, SO2, and H2O
• Magmas are thus complex bodies and the rocks derived from them
have a wide variety of composition.
• Cooled quickly, a magma solidifies as a rock-glass, without
crystals; cooled slowly, rock-forming minerals crystallize out from
it.
• The content of silica (as SiO2) in igneous rocks varies from over
80% to about 40% and results in some, e.g. granites, containing
visible quartz (SiO2) and others, e.g. gabbros, having no quartz
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Types of Rocks
Classification of Igneous Rock: On the basis texture (size, shape and
arrangement of mineral grains in a rock) and mode of occurrence,
Igneous rock is divided broadly into two types:
1. Intrusive (also called plutonic rocks): form below the ground
surface, where they cool slowly,
2. Extrusive (also called volcanic rocks) arrive at the ground surface
in a molten state, such as through volcanic eruption. This type of
igneous rock cool very rapidly.
Structures of Igneous Rock.
Legend: A = magma chamber (batholith); B =
dyke/dike;
C = laccolith;
D = pegmatite;
E = sill;
F = stratovolcano;
processes: 1 = newer intrusion cutting through older
one;
2 = xenolith or roof pendant;
3 = contact metamorphism;
4 = uplift due to laccolith emplacement.
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Volcanoes and Extrusive Rocks
•
•
•
•
•
During an eruption lava is extruded from the volcanic vent and
gases contained in the lava are separated from it.
They may be discharged quietly if the lava is very fluid and the
gas content small, but commonly they are discharged with
explosive violence.
Different styles of volcanic action are distinguished as
i) fissure eruptions: Lava issues quietly from long cracks in the
Earth's surface, with little gas emission.
ii) central eruptions: A central eruption builds a volcano that
has a cone with a summit crater connected to the volcanic 'pipe',
through which are ejected lava, gases, and fragments of
exploded lava (ash) and broken rock. Vesuvius, Etna, and
Stromboli in the Mediterranean region, Popocatapetl, and
Cotopaxi in the Andes, the Mounts St Helens, Rainier, Crater
Lake, Shaster and Lassen Peak in the Cascades of N. America,
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Volcanic Eruptions
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Igneous Rocks-Volcanic Eruption
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Intrusive rocks and rock forms
• A body of magma in the Earth's crust may rise to higher levels
and penetrate the rocks above it without reaching the surface;
it is then said to be intrusive.
• A large mass of magma, many cubic km in volume, is a major
intrusion and cools slowly because of its size. Large crystals
are able to form and the rocks so formed are coarsely
crystalline
• When the magma rises and fills fractures or other openings in
the country-rocks ,it forms minor intrusions, i.e. smaller
igneous bodies. These include dykes, which are wall-like
masses, steep or vertical, with approximately parallel sides
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Major intrusions
Plutons, stocks, and batholiths
• The term pluton is used to denote a moderately large body of
magma which is intruded essentially at one time and is contained
within a single boundary. Plutons have various shapes but are
commonly nearly circular in cross-section; an average area for
many granitic plutons is about 150 km2 but many are larger
• The older term stock was introduced by R.A. Daly (1912) to
denote a vertical nearly cylindrical body of igneous rock, cutting
across the rocks into which it is intruded, with a cross-sectional
area up to 100 km2
• Most batholiths consist of a cluster of plutons, located by some
structural control during their intrusion. Examples in Britain are the
Donegal batholith, Ireland, which consists of 8 separate plutons
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Composition of Igneous Rocks
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Igneous Rocks
Hypabyssal
Rock:
Hypabyssal
rocks
are
formed
when
consolidation of magma takes place very close to the earth’s
surface in the form of smaller sheet like bodies (known as sills and
dykes) that fill cracks inside other rocks.
Some extrusive rocks generally have finer grained, smoother
surfaces. Some extrusive materials, such as volcanic ash, bypasses
the rock stage and forms directly into sediment
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Close-up of granite (an intrusive igneous rock) exposed
Basalt (an extrusive igneous rock in this case); light colored tracks
show the direction of lava flow.
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Gabbros Specimen
Granite containing potassium feldspar, plagioclase feldspar,
quartz, and biotite and/or amphibole
Common Igneous Rocks
Some common igneous rocks include:
Granite: is coarse grained, an intrusive rock. It is the most common
and familiar igneous rocks. Granite contains primarily orthoclase
feldspar and quartz, with some biotite and amphibole. It is mostly light
in color with a white or pink tint according to the color of the feldspar.
Engineering properties:
Granite have absorption as low as 0.24 per cent.
It has an excellent frost resistance.
Because of the minerals composition and interlocking of crystals, granite is hard
and abrasion resistant.
The compressive strength of granite is on average 24,500 psi.
It can be concluded that granite can be used to support any load of ordinary
structures.
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Common Igneous Rocks
Diorite: is coarse grained, an intrusive rock. It is mainly composed
of plagioclase feldspar (more than 50 %) and horn blends.
However, in some varieties augite and biotite may be present. It is
more abundant than syenites but less abundant than granite.
Diorite has been used for crushed stone for monumental and
decorative purposes than for structural purposes.
Syenite: is grained igneous rocks composed essentially of
potassium felspare (80-85 %). Biotite and hornblende are
commonly present. Quartz is present in small amount. The general
properties of syenites is similar to granite. Because of the rarity of
syenite, it is of little commercial use as structural material.
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Common Igneous Rocks
Some other types of igneous rocks are: Rhyolite, Pumice (can be
used as pozzolanic materials with cement), Dolerite, Basalt and
Gabbro.
Texture: Texture is size, shape and arrangement of mineral grains
in a rock. Texture of rock can either of coarse-crystalline or it can
be glassy or amorphous. The texture of the rock is governed by the
cooling time of the magma. Crystallization is governed by slow
cooling, however, glassy texture or amorphous form is the result of
rapid cooling.
Types of rock: Holocrystalline, Coarse grained, fine grained,
cryptocrystalline and glassy (amorphous)
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Dike and sill
Sill: A sill is igneous rock which vary in thickness from a few centimeter to
several hundred meters. The sill is parallel to the bedding of rock and may be
horizontal, inclined or vertical depending upon the strata.
Dike: A dike is vertical wall-like igneous body that cuts the bedding of the rock.
The thickness of the dike may vary from a few centimeters to a hundred meter
or more.
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Geological significance of Igneous Rocks
The upper 16 kilometers (10 mi) of Earth's crust is composed of
approximately 95% igneous rocks with only a thin, widespread covering of
sedimentary and metamorphic rocks.
Igneous rocks are geologically important because:
 Their minerals and global chemistry give information about the
composition of the mantle, from which some igneous rocks are extracted,
and the temperature and pressure conditions that allowed this extraction,
and/or of other pre-existing rock that melted;
Their absolute ages can be obtained from various forms of radiometric
dating and thus can be compared to adjacent geological strata, allowing a
time sequence of events;
Their features are usually characteristic of a specific tectonic
environment, allowing tectonic reconstitutions.
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Common Igneous Rocks
Geological significance of Igneous Rocks
In some special circumstances they host important mineral deposits (ores):
for example, tungsten, tin, and uranium are commonly associated with
granites and diorites, whereas ores of chromium and platinum are
commonly associated with gabbros.
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Uses of Igneous Rocks (granites)
Because they are so hard, Igneous rocks make useful road building materials.
When sheets of igneous rock are cut and polished, they are used inside
buildings such as banks and offices, and are also used as gravestones.
There are different types of igneous rock, therefore each type has its own
uses, such as:
Granite: Used for long lasting monuments, for trim and decoration on
buildings.
Pumice: Because they are so light, it is used quite often as a decorative
landscape stone. If grounded to a powder, it is used as an abrasive in polish
compound.
Crystalline Igneous rocks can be used for jewelry and other similar things.
Countertops and building stone.
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Sedimentary Rocks
1. Classification of sedimentary Rock
2. Description of common sedimentary rock
3. Types of metamorphism
4. Description of common metamorphic rock
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Classification of Sedimentary Rocks
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.
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Development
• The components of sediments become hardened into sedimentary
rocks such as sandstone, quartzite, limestone and shale by changes
which commence soon after the sediment has accumulated.
• Water percolating through the voids (or pores) between the
particles of sediment carries mineral matter which coats the grains
and acts as a cement that binds them together such processes are
known as cementation', they may eventually completely fill the
pores and are responsible for converting many coarse-grained
sediments to rock
• In course of time mud will become a coherent mass of clay,
mudstone, or shale
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Classification of Sedimentary Rocks
Sedimentary rock is formed by deposition and consolidation of minerals and
organic materials and from precipitation of minerals from solution. The
processes that form sedimentary rock occur at the surface of the earth and
within bodies of water.
Rock formed from sediments covers 70-80 % of the earth’s land area, and
includes common types such as limestone, chalk, sandstone, conglomerate and
shale.
Sedimentary rocks are only a thin veneer over a crust consisting mainly of
igneous and metamorphic rocks and constitute a total of 5% of the earth crust
volume.
Sedimentary rocks are deposited in layers as strata, forming a structure called
bedding. The study of sedimentary rocks and rock strata provides information
about the subsurface that is useful for civil engineering, for example in the
construction of roads, houses, tunnels canals or other constructions.
Sedimentary rocks are also important sources of natural resources like coal,
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fossil fuels, drinking water or ores.
Classification of Sedimentary Rocks
The scientific discipline that studies the properties and origin of sedimentary
rocks is called sedimentology.
Sedimentology is both part of geology and physical geography and overlaps
partly with other disciplines in the Earth sciences, such as penology,
geomorphology, geochemistry or structural geology.
The study of the sequence of sedimentary rock strata is the main source for
scientific knowledge about the Earth's history, including palaeogeography,
paleoclimatology and the history of life.
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Classification of Sedimentary Rocks
Mechanically formed: consisting of materials (gravels, sand, silt and clay)
suspended in flowing water. The suspended materials are then deposited and
consolidated.
Water percolates into cracks and fissures within the rock, freezes, and
expands. The force exerted by the expansion is sufficient to widen cracks and
break off pieces of rock. Heating and cooling of the rock, and the resulting
expansion and contraction, also aids the process. Mechanical weathering
contributes further to the breakdown of rock by increasing the surface area
exposed to chemical agents.
The mechanically formed sedimentary rocks are of three types:
1. Rudaceous rocks which is the cementing together of boulders, for example,
conglomerate.
2. Arenaceous rocks for example sandstone,
3. Argillaceous rocks which is clay rocks for example shale
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Clay stone deposited in Glacial Lake
Missoula, Montana, USA.
Outcrop of Ordovician oil shaleNorthern Estonia.
Cross-bedding and scour in a fine sandstone.
Cyclic alternation of competent 33
and less
competent beds in the Blue Lias
Classification of Sedimentary Rocks
Organically formed: Consisting of accumulated animals and plants
remains.
Organic sedimentary rocks contain materials generated by living
organisms, and include carbonate minerals created by organisms, such as
corals, mollusks (Snail, slug, Octopus) , and foraminifera (seawater
Organism) , which cover the ocean floor with layers of calcium carbonate,
which can later form limestone. Other examples include stromatolites, the
flint nodules found in chalk (which is itself a biochemical sedimentary
rock, a form of limestone), and coal and oil shale (derived from the
remains of tropical plants and subjected to heat).
They are:
1. Calcareous rocks, lime stone
2. Carbonaceous rocks, coal
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Classification of Sedimentary Rocks
Chemically formed: this type of rocks is formed by precipitation and
accumulation of soluble constituents.
Chemical sedimentary rocks form when minerals in solution become
supersaturated and precipitate. In marine environments, this is a method for
the formation of limestone. Another common environment in which chemical
sedimentary rocks form is a body of water that is evaporating. Evaporation
decreases the amount of water without decreasing the amount of dissolved
material. Therefore, the dissolved material can become oversaturated and
precipitate. Sedimentary rocks from this process can include the evaporite
minerals halite (rock salt), sylvite, barite and gypsum.
These are
1. Carbonate rocks, Limestone, dolomite
2. Sulphate rocks, Gypsum
3. Chloride rocks, salt
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Consolidation
Consolidation is a process by which soft and loose sediments are
converted into hard and firm rocks. Consolidation is of three types:
1. Compaction and Dehydration: The squeezing out of water from the
pores of the sediments and its changing to solid mass by cohesion
between the particles and pressure from overlying rock is called
compaction and dehydration.
2. Cementation: Many coarse grained sediments are consolidated by
cementation, which is the process of precipitation of some cementing
materials, for example, silica, calcium carbonate, iron oxides and clay
minerals.
3. Crystallization: Chemically formed sedimentary rocks such as
limestone, dolomites, gypsum etc are consolidated chiefly by the
crystallization of their constituents.
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Structural Features
Structural features of sedimentary rocks are of great value in
determining their origin. The main structures are as follows:
Stratification: The deposition of sediments into layer or beds is called
stratification. The thickness of a single bed may vary from a few
centimeters to many meters. The stratification is formed due to the
following.
I. Difference in the kinds of materials deposited for example shale and
lime stone
II. Difference in the size of particles deposited for example coarse
grained and fine grained sandstone beds
III.Difference in the color of the materials deposited for example light
grey and dark grey layers of limestone
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Lamination: Thin bedding, less than one centimeter in thickness,
are called lamination. It is usually fined grained sedimentary
rocks like shales.
Cross-bedding: It is also called current bedding or false bedding.
Cross-bedding are the minor bedding or lamination which lie
at an angle to the planes of general stratification. This
structure is found in shallow water and wind formed deposits.
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Different types of sedimentary rocks
Conglomerate: The pebbles and gravels on consolidation and cementation
produce a rock known as conglomerate. Gravels are deposited for the most
part by water. Water circulating through gravel deposits may precipitate out
silica, calcium carbonate, or iron oxides, which act as cements binding the
gravels together into conglomerates.
Sandstones: Most sand is a water deposit. In arid regions, widespread sands
have been laid down by wind action. Volcanic eruptions, glacial action,
mechanical and chemical weathering, and organisms produce sands. The
sand particles are deposited and then cemented together by materials like
silica, calcite, iron oxide or clay. Sandstones may be siliceous sandstone that
is the cementing materials is silica; it may be calcarious sandstone in which
the cementing materials is calcium carbonate; ferruginous sandstone and
argillaceous sandstone having iron oxide and clay as cementing materials
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Different types of sedimentary rocks
The thoroughly cemented sandstone with quartz are termed as
orthoquartzite.
Argillaceous rocks: variously called mudstone, claystone, and shale
(compacted or cemented) are among the most abundant of sedimentary
rocks. It is a laminated fine grained sedimentary rock which is mainly
composed of clay minerals and some silt-size grains of quartz.
The claystones, because they are characteristically soft and weak are not
suited to most construction purposes. The compacted shale lose strength
when wet and are subject to plastic deformation. Under load they are
subject to failure by flow. The cemented shales have a strength comparable
to concrete but have a relatively high elasticity. Clay stones underlying the
sites of heavy structures should be test in both wet and dry conditions. Clay
stone has a limited use. It serves as a raw materials for the ceramic industry
in some places and also used as raw materials for cement production.
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Different types of sedimentary rocks
Carbonate rocks: The carbonate rocks are chiefly the products of marine
or fresh water sedimentation. They are predominantly chemical sediments
either formed by metabolic process of organism or precipitated
inorgainically. Mineralogically, the carbonate rocks are comparatively
simple. There are two main varieties; the limestone composed chiefly of the
calcite, and the dolomite composed chiefly of dolomite.
The carbonate rocks, particularly the limestones, have a very wide use in
modern industry. The largest single use is as crushed stone. Limestone is
one of the leading dimension stones being utilized both for internal and
external work. Commercial lime is derived from the burning of limestone.
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Quartzite, a form of metamorphic rock,
Metamorphic Rocks
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Metamorphic rocks
Metamorphic rock is the result of the transformation of an existing rock
type, the protolith, in a process called metamorphism, which means "change
in form".
When the pre-existing rocks (sedimentary or igneous rock) are subjected to
increased temperature, pressure and action of chemically active fluids,
metamorphic rocks are formed. During metamorphism re-crystallization of
mineral constituent takes place, as a result new minerals and new texture are
produced.
The metamorphic processes generally improve the engineering behavior of
these rocks by increasing their hardness and strength. Nevertheless, some
metamorphic rocks still can be problematic. Some metamorphic rocks are
foliated, which means they have oriented grains similar to bedding plains in
sedimentary rocks. These foliation is important because the shear strength is
less for stresses acting parallel to the foliation.
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Metamorphic rocks
Un-weathered non-foliated rocks generally provide excellent support for
engineering works, and are similar to intrusive igneous rocks in their quality.
However, some foliated rocks are prone to slippage along the foliation planes.
Schist is the most notable in this regard because of its strong foliation ad the
presence of mica. The 1928 failure St.Fancis Dam in California has been
partially attributed to shearing in schist and the 1959 failure of Malpasset
dam in France to shearing in a schistose gneiss.
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Folded foliation in a metamorphic rock
Types of Metamorphism
Contact metamorphism is the name given to the changes that take place
when magma is injected into the surrounding solid rock. The changes that
occur are greatest wherever the magma comes into contact with the rock
because the temperature are highest at this boundary and decrease with
distance from it. Around the igneous rock that forms from the cooling
magma is a metamorphosed zone called a contact metamorphism aureole.
-shale may become a dark argillaceous hornfels,
-Limestone may change to a grey, yellow or greenish
lime-silicate-hornfels or siliceous marble,
A contact metamorphic rock made of
inter layered calcite and serpentine
from the Precambrian of Canada
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Types of Metamorphism
Regional metamorphism is the name given to changes in great masses of
rock over a wide area. Rock can be metamorphosed simply by being at
great depths below the earth’s surface, subjected to high temperatures
and the great pressure caused by the immense weight of the rock layers
above. Much of the lower continental crust is metamorphic.
Mississippian marble in Big Cottonwood
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Different Metamorphic rocks
Marble: Marbles are metamorphosed carbonate rocks, derived from
limestones and dolomites. The color of marble is variable, however, if the
rock is pure calcite or dolomite marble it is generally white. Various
impurities give rise to various shades. Green, pinks and buffs are common
shades.
The principal uses of marble are as cut stone for building and ornamental or
decorative use.
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Different Metamorphic rocks
Slate: Slate is a dense metamorphic rock, with a strongly developed
foliation. It is produced by the metamorphism of shale. The rock
cleavage, or split-ability is therefore excellent and is the outstanding
characteristic of slates. The color of slate varies from iron-tinted reds
through various shades of gray and green. The gray shades are due to
carbonaceous matter, the greens to chloritic micas. The texture of slates
is very fine or dense and foliation is good to perfect.
Slate is used widely in the electrical industries as switchboards.
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Different Metamorphic rocks
Phyllite: Phyllite are strongly foliated metamorphic rocks similar to the
slates but of slightly coarser texture. Phyllite have shiny luster due the
presence of large amount of fine flakes of mica. Phyllite gradually pass into
slates which are the first stage in the metaphorphism of shale.
It has little use. It is too soft for crushed stone, and too weak for structural
uses.
Schist: Schist are foliated metamorphic rocks of medium to coarse texture.
They are the product of the same processes of rock flow and recrystallization
that produce slates and phyllite. The color of schist vary according to the
mineralogical composition, as does also the perfection of cleavage.
Schist has of little use. Because of the foliation, they are generally weak
rocks. Some schists especially rich in muscovite are a source of scrap mica.
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