Sedimentary Petrology
SEDIMENTARY ROCKS
Disintegration
Decomposition
(Mechanical)
(Chemical)
Air
Water
Temperature
Frost
Chemical
changes
Abrasion
by ice
Wind
Decay resulting in weathering
The decomposition and disintegration of rocks on the earth’s
surface usually occur together, but one process is usually
predominant.
Decomposition is more active in warm, moist, low-lying areas;
disintegration occurs mainly in the drier, higher and colder
regions of the earth’s surface.
DECOMPOSITION: The principal AGENTS of decomposition are water
and air. The chief PROCESSES of decomposition are solution,
oxidation, hydration and carbonation. Nearly all minerals are
acted upon to some extent by water, especially when it contains
certain dissolved substances. Some, however, are more susceptible
than others and minerals may thus be divided into those which are
relatively resistant, such as quartz, muscovite and zircon, and
those which are altered with comparative ease, such as the
feldspars and most of the ferromagnesian minerals.
The process of oxidation involves the alteration of minerals,
with the production of oxides. It is especially active with ironbearing minerals, forming the iron oxides haematite and limonite.
Hydration is a process by which minerals are altered into
substances rich in combined water. Magnesium-bearing minerals,
such as olivine, are thus altered into serpentine and talc.
(Mg,Fe)2SiO4  Mg6[Si4O10](OH)
(olivine)
(serpentine)
In carbonation, the minerals are altered, with the formation of
carbonates. It is especially effective with those minerals
containing the alkali metals sodium and potassium, as well as
calcium and magnesium.
The decomposition of a granite furnishes many different kinds of
minerals:
 Unaltered minerals: Includes quartz and zircon, which form
sand grains. Muscovite produces mica grains.
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 Insoluble residues: Includes hydrous aluminium silicates,
which are fundamental constituents of clays; and iron oxides,
which are the colour matters of rocks.
 Soluble substances: Includes salts of potassium, sodium,
calcium, magnesium, iron, etc., and silica.
DISINTEGRATION: In high mountains, deserts and snow- or icecovered regions, the process of decomposition is largely in
abeyance and disintegration is the dominant mode of breaking down
rocks. Disintegration may result from a variety of causes. The
great diurnal variations of temperature in deserts and
mountainous regions cause strains to be set up in the surface
layers of rocks, by which fragments are scaled off. The process
is known as exfoliation. The freezing of water in fissures tends
to disrupt rocks into angular fragments and much of the
weathering in high mountains takes place in this way, the summits
being covered with a thick layer of rock debris. The abrasive
action of sand carried by wind or water causes the disintegration
of rocks in deserts, or in the channels of swift-running, sandladen rivers. Glaciers my pluck and rend boulders from their
beds; and by their slow restless movement grind the material they
carry against the sides of the containing valleys, with the
formation of sand and mud. Most streams issuing from glaciers are
heavily laden with materials derived from this action. The
pounding of waves may result in much disintegrative action, as is
proved by extensive coast erosion. Finally, organic agents often
have a marked mechanical effect upon rocks. The roots of plants
prise open the fissures or rocks in their search for moisture and
nourishment; burrowing animals turn over the soil and subsoil;
and man himself, by tilling the ground, deforestation,
tunnelling, quarrying, mining and in numerous other ways, helps
to disintegrate the rocks.
By disintegration, a granite will break up into a coarse sand
composed of fragments of quartz, feldspar and micas, mixed with
pieces of rock not yet broken down into the component minerals.
Many granite areas carry sands of this composition, which are
called arkose sands, or, when accumulated, arkose. A basic rock
broken up in the same way gives rise to a rock called wacke or
greywacke, which is composed of plagioclase feldspar,
ferromagnesian minerals and quartz. Disintegration may also
produce rough, angular rubble consisting of any kind of rock,
which may mantle a mountain-top or accumulate by the action of
gravity at the foot of a slope. These accumulations are called
talus or scree when unconsolidated, and breccia when consolidated
or cemented into a coherent mass. The resultant of the twin
processes of decomposition and disintegration is weathering, and
the product thereof, in the first place, is the mantle of loose,
broken and largely decomposed material, the regolith, which
covers the surface of the earth. The finely broke upper layer of
the regolith, well aerated and mixed with decayed organic matter,
is the soil.
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TRANSPORTATION: The soluble or insoluble material supplied by
weathering is either accumulated in place or is transported and
deposited elsewhere. The agents of transport are rivers, waves,
oceans currents, wind, and glaciers. The loess of China is
believed to be simply an extensive deposit of wind-blown dust
derived from the Asian deserts. Wind is by far the most efficient
agent of rounding, and grains which have suffered long transport
by wind show almost perfect spherical forms. Ice transport,
however, permits very little rounding. Wind, again, is the most
efficient sorted of grains, and deposits carried by wind are
often characterised by their homogeneity. In ice transport,
however, there is little or no sorting of materials, and on
melting or retreat of the ice, it is dumped down into an
unassorted and heterogeneous mixture of rock flour, grains,
pebbles and boulders of all sizes.
DEPOSITION: The ultimate destination of transported material,
whether carried by water, wind or ice, is the sea, but it may be
temporarily deposited on the land, and the deposits thus formed
may persist for several geological periods before they resume
their march to the sea. This leads to a distinction between
continental and marine deposits. Deposition may be either
mechanical or chemical, according to whether it affects the
mechanically transported insoluble material or the substances
carried in solution. The material carried in suspension or in
other ways by water, wind and ice is deposited when the
transporting medium is overloaded, when its velocity is checked,
or when it suffers a chemical or physical change. Very extensive
deposits of clay, silt and sand thus occur in the lower parts of
river systems and also where rivers debauch into the sea(in
deltas). The settlement of material entering the sea is aided not
only by decrease in velocity of the river current, but also by
admixture of salt water, which promotes a physical change
(flocculation) favourable to the deposition of suspended
material.
The soluble material derived from weathering may be deposited
either on land or in water, directly by physicochemical processes
such as precipitation, or indirectly by the agency of organisms.
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Sedimentary Rocks
MINERALOGICAL, TEXTURAL AND STRUCTURAL CHARACTERS:
 Mineral composition: The minerals of sedimentary rocks fall
into two classes:
 Insoluble residues of rock decomposition: This includes the
groups of:
 Clay minerals such as kaolinite, halloysite, etc.
 Micaceous minerals, including the hydromicas and chlorite.
 Aluminium hydroxides like bauxite, gibbsite, etc.
 Ferric oxides and hydroxides.
 Comparatively durable minerals from pre-existing rocks.
These include:
 Quartz (most abundant)
 Accessory minerals like zircon, rutile, tourmaline,
garnet, kyanite, magnetite, etc.
Mineral composition also depends upon the nature of the rocks
forming the gathering round of the material. If the country
rock consists mainly of some mineralogically uniform rock such
as quartzite or a granite poor in ferromagnesian minerals and
accessory minerals, the composition of the sediment resulting
from its denudation will be simpler than that resulting from
the waste of a lithologically or mineralogically heterogeneous
region. The duration and nature of the transport is also a
factor in determining the mineral composition. Long, continued
drifting of particles separates them according to mass and
surface area, and therefore according to composition. Wind is
a particularly efficient sorter of sand grains. In deserts,
mica flakes and dust are blown far away, and the remaining
sands are sifted and redistributed until there is an approach
to mineral uniformity. Long, continued transport in rivers or
along shores may be almost equally effective in producing
clean, graded and uniform deposits. Transportation tends to
destroy the softer, more cleavable and brittle mineral grains,
and thus produces greater mineral uniformity in the final
material.
Those constituents, such as boulders, pebbles or mineral
grains which have been formed elsewhere and have been brought
into a sediment from outside are termed allogenic (originating
elsewhere); those constituents which have been formed de
novo/in situ are called authigenic (formed in place or on the
spot).
TEXTURES OF SEDIMENTARY ROCKS:
Textures of sedimentary rocks are defined by at least six
factors:
 Origin Of Grains: A sedimentary rock may be partially or
wholly composed of clastic(allogenic) grains, or chemically or
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organically evolved(authigenic) components, giving it
contrasting textures. Thus, rocks rich in clastic grains of
any size, shape and composition are said to show clastic
textures and these form the two principle types of sedimentary
textures.
 Size OF Grains: The grain size in sedimentary rocks varies
within wide limits. Individual grains of less than 0.002mm or
more than 250mm may form a part or whole of these rocks.
Accordingly, rocks are divided into fine grained (grain size <
1mm), medium grained (grain size between 1mm and 5mm) and
course grained (grain size > 5mm). The type of weathering, the
nature of the parent rock and the duration of transport are
some of the factors that cause a variation in the grain size
of the sediments.
HOLMES’ CLASSIFICATION OF SEDIMENTARY FRAGMENTS:
GRADE
Boulders
Cobbles
Pebbles
Gravel
Very Coarse Sand
Coarse Sand
Medium Sand
Fine Sand
Silt
Dust, Mud & Clay
SIZE RANGE
>200mm
200mm - 50mm
50mm - 10mm
10mm - 2mm
2mm - 1mm
1mm - 0.5mm
0.5mm - 0.25mm
0.25mm - 0.10mm
0.10mm - 0.01mm
<0.01mm
MAIN GROUP
RUDYTES
GRAVEL
SAND
SILT
CLAY
WENTWORTH-UDDEN SCALE (SI):
SIZE RANGE
> 265mm
64mm - 256mm
4mm - 64mm
2mm - 4mm
1/16mm - 2mm
½56mm - 1/16mm
< 1/256mm
PARTICLE
Boulder
Cobble
Pebble
Gravel
Sand
Silt
Clay
 Shape Of Grains: Individual outlines of sediments are
generally of considerable significance in defining the
textural characteristics. These grains may be round, smooth
and spherical, or angular or rough. Roundness and sphericity
are the indications of a greater amount of abrasion and
generally of a large amount of transportation in the clastic
rocks.
 Packing of the Grains: Sediments may be open-packed or closepacked. The density of the packing is generally related to the
pressure, either from above (because of overlying strata) or
from the sides (because of compressive forces originating
during mountain-building periods).
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 Fabric of the Grains: A given sedimentary rock may contain
many elongated particles. Their orientation, which is studied
in terms of their long axis, is of great textural importance.
If all or most of the elongated particles are arranged in such
a way that their long axes lie in the same direction, the rock
is said to show a high degree of preferred orientation. The
direction of preferred orientation is commonly related to the
direction of the current flow of the medium of transport.
 Crystallisation Trends: In sedimentary rocks of chemical
origin, textures are usually defined on the basis of degree
and nature of crystallisation of the component grains. Rocks
may show perfectly interlocking grains, giving rise to
crystalline granular textures, or they may be composed of noncrystalline, colloidal particles, when textures are termed
amorphous.
STRUCTURES OF SEDIMENTARY ROCKS:
The term structure includes some large-scale features of the
sedimentary rocks that have been imposed on them during their
formation. These can be best studied under three headings:
 Mechanical Structures
 Chemical Structures
 Organic Structures
 Mechanical Structures: They include those structures that have
developed because of some physical processes operating at the
time of deposition of the sediments. These include:
 Stratification: By stratification is understood a layered
arrangement in a sedimentary rock and this may be very
prominent or only mildly displayed. The different layers may
be of similar or dissimilar colour, grain size and
composition. These layers, also known as beds or strata if
more than 1 cm thick, are separated from each other by
planes of weakness - the bedding planes. When the bedding
planes are very close to each other, or, in other words, the
beds are very thin (generally <1cm thick), the term
lamination is used instead of stratification, and the layers
are known as laminae. Lamination is a characteristic feature
of very fine-grained rocks like shale.
 Cross Bedding: Changes in velocity and direction of the
currents of the transporting agent result in an irregular
type of stratification, variously called false bedding,
current bedding or cross bedding. The cross-bedding is
described as tabular when successive sets have essentially
parallel top and bottom surfaces. It is termed as lenticular
when layers show extreme irregularity in their shape and
disposition; each layer or set of beds may be intersected by
other lying at different angles. The cross-bedding is known
as wedge-shaped when the structure is highly complex; the
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laminae of different beds dip in different direction and at
different angles.
Tabular Bedding
Lenticular Bedding
Wedge-Shaped Bedding
 Graded Bedding: In some stratified rocks, the component
sediments in each layer appear to be characteristically
sorted and arranged according to their grain size, i.e. the
coarsest being towards the bottom and the finest towards the
top of each of the two layers. Such an individual layer is
said to be graded and if a number of such graded beds occur
one above the another, as invariable is the case, the
structure is termed as graded bedding. Normally, such beds
are the result of sedimentation in bodies of standing water
where there are seasonal variations in the process.
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 Mud Cracks: They are features of common observation in
those sedimentary masses of fine grain size that have
been exposed to drying under sub-aerial (i.e. under the
influence of sun rays) conditions.
 Rain Prints: They are the marks left on the top surface
of loose sediments by rain water.
 Ripple marks: They are symmetrical or asymmetrical
undulations that may be seen on some sedimentary
deposits. These are essentially the product of wind or
wave action during the deposition of sediments in a
shallow water environment.
 Chemical Structures: These include those types that result
during the segregation of the surfaces through chemical
processes. Some important chemical sedimentary structures
are:
 Concretionary Structure: Concretions are rounded,
nodular, or irregularly shaped material present in some
rock masses. Their chemical and mineralogical composition
is generally different from the enclosing rock.
 Oolitic & Pisolitic Structures: The presence of small,
more or less spherical particles (ranging from 0.1mm to
1mm), called oolites, give rise to the oolitic structure.
Sometimes these particles are of bigger size (>2mm) and
are termed pisolites; the structure is termed pisolitic.
Limestones and bauxites show both structures.
 Nodular Structure: This structure is exhibited generally
by limestones and s characterised by the development of
irregularly shaped nodules of chert, iron oxides, iron
carbonates and clay ironstone. Sometimes, these nodules
show an elongation or flattening parallel to the bedding
planes.
 Geode structure: A geode is actually a hollow shell, the
interior or which is lines with inwardly projecting
crystals. Generally, the outer shell is made of
chalcedony and the inner encrustations are of quartz
crystals. The formation of a geode requires the presence
of an original cavity.
 Organic Structures: They include those structural features
that have been imposed, directly or indirectly, by the
organisms on sedimentary rocks. The rock is described as
fossiliferous if it contains remains of some organisms.
Limestones are sometimes highly fossiliferous. Another kind of
structure which is produced by some kinds of algae is termed
stromatolitic.
CLASSIFICATION OF SEDIMENTARY ROCKS:
Sedimentary rocks have been variously classified on the basis of
their mineralogical composition, environment of deposition, mode
of formation and textural/structural features. In the
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classification, all sedimentary rocks are grouped under two
divisions:
 Clastic (Detrital)
 Non-Clastic (Chemical)
 CLASTIC(MECHANICALLY FORMED)ROCKS: Clastic rocks include all
those sedimentary rocks that have been formed from preexisting rocks through the mechanical action of denuding
agents like wind, water, glaciers, etc. Their formation is
achieved through the processes of erosion, deposition and
lithification of the sediments. The clastic rocks are further
subdivided into the following three classes on the basis of
average grain size of the sediments:
 Rudites/Rudaceous rocks/Psephites: These include coarsegrained clastic rocks of heterogeneous composition. The
average grain size of the sediments of rudites is always
more than 2mm. In other words, they may composed of
boulders(>200mm), cobbles(200mm-50mm), pebbles(50mm-10mm)
and gravel(10mm-2mm) that are generally held together by
cementing material. For example, breccia and conglomerate.
 Arenites/Arenaceous rocks/Psammites: They include mediumgrained clastic rocks. These are made up of sediments of
grain size between 2mm and 1/16mm. Most commonly the grains
are siliceous in composition; sandstones, greywackes, arkose
and quartzite are some common examples.
 Lutites/Argillaceous rocks/Pelites: These are the finest
grained clastic rocks which are made up of sediments with
average grain size less that 1/256mm. They include common
rocks such as shale, mudstone, claystone, etc. Clastic rocks
with particles of grain size between 1/16mm and 1/256mm are
also grouped under lutites, although they are generally
described as silt rocks. Siltstone is a common example.
 NON-CLASTIC (CHEMICALLY FORMED) ROCKS: These include
sedimentary rocks that have been formed through
precipitation/evaporation of natural solutions. These also
include the sedimentary rocks of organic origin in which the
process of formation has been distinctly biochemical in
nature. Non-detrital rocks are generally homogeneous in
character, with interlocking crystalline texture and are
formed mostly at the site of deposition. They are further
divided into two main classes, namely the precipitates and the
organic rocks.
 Precipitates: The group includes sedimentary rocks that have
been formed as a result of chemical processes like
crystallisation, precipitation and evaporation from aqueous
solutions carrying the weathered material dissolved in them.
On the basis of chemical composition, the precipitates are
further divided into:
 Siliceous deposits: Here silica is the chief constituent.
Some forms of silica like chalcedony, opal, etc. are
slightly soluble in water and may be deposited in various
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forms, forming siliceous deposits. E.g. flint, jasper,
chert.
 Carbonate deposits: They include sedimentary rocks of
carbonate composition, chief among which are carbonates
of calcium and magnesium that form widespread deposits of
limestone and dolomite.
 Ferruginous deposits: These include sedimentary rocks of
ferruginous composition and chemical origin. Generally,
they are composed of oxides and hydroxides of the metal,
though carbonates and silicates are also formed. The socalled bog iron ores are chemically precipitated
hydroxides or iron.
 Phosphatic deposits: Common example of phosphatic
deposits are rock phosphates that have formed from sea
water rich in phosphoric acid. Similarly, other rocks
like limestones and shales may be rich in phosphate
content.
 Evaporites: They are the chemically formed sedimentary
rocks in which evaporation is the process involved. These
include some of the very important sedimentary deposits
of economic value like gypsum, rock salt, anhydrite,
calcium carbonate, borate, rock sulphur and nitrate. The
deposits have formed from bodies of sea water that were
detached from the ocean because of any reason and were
then concentrated to the point of saturation and
subsequent precipitation under continued evaporation.
 Organic deposits: Those sedimentary deposits in the
formation of which organisms (both plants and animals) have
played a prominent part are grouped under this heading. The
organisms might have contributed directly or indirectly.
Thus rocks in which the bulk of the material is supplied by
organisms (as, for instance, coal and some limestones) are
simply the refined remains of some plants and animals
respectively. Indirect contribution is made in a different
way; some types of bacteria may help or even be solely
responsible from precipitating the rock components from
solutions. Organic deposits are further distinguished into
the following types on the basis of their chemical
composition:
 Carbonate rocks: These are formed by gradual accumulation
of shells and skeletons of sea animals like foraminifera,
corals, crinoids and crustacea. Some types of limestone
are purely organic in origin.
 Carbonaceous rocks: These are the sedimentary deposits
rich in carbon. In these, the raw material have mostly
been supplied by plants of various groups. Most important
of such deposits are coals of various types.
 Phosphatic deposits: Guano is an example of the
phosphatic deposits of organic origin. The guano deposits
are actually accumulations of phosphatic excreta of
certain birds that inhabit certain islands and live
mainly on fish.
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
Ferruginous deposits: These include some iron deposits in
the precipitation of which certain types of bacteria are
believed to have taken active part.
 Miscellaneous deposits: Some sedimentary rocks have a
complex mode of formation, and thus cannot be easily grouped
under any of the above headings of non-clastic rocks. It is
customary to describe them separately. Some of these are
clearly of residual nature, i.e. they were formed by the
decomposition of pre-existing rocks involving their
alteration into new types. Examples of such deposits are
bauxite and laterite.
TABULAR CLASSIFICATION OF SEDIMENTARY ROCKS
COMPOSITION
Siliceous
Argillaceous
Calcareous
Carbonaceous
Ferruginous
Miscellaneous
CLASTIC
ROCKS
RUDITES
(>2mm)
a)Breccia
b)Conglomerate
ARENTES
Sandstone
LUTITES (21/256mm)
Shale
Clay
Siltstone
Marls
Calcareous
conglomerates and
sandstones
Carbonaceous shale
Ferruginous
sandstones
-
NON-CLASTIC
ROCKS
1. Flint
ORGANIC
ROCKS
Radiolarian
earth
RESIDUAL
ROCKS
2.Chert
3.Siliceous
Sinter
Diatomaceous earth
-
-
-
Limestones
Kankar
Travertine
COALS:
Lignite
Bituminous
coal
Anthracite
Bog iron
ore
SALTS:
Gypsum
Anhydrite
Rock salt
Caliche
Phosphate
rocks
Limestone
Chalk
Some iron
ores
Phosphate
rocks
Guano
CLASTIC ROCKS:
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Terra Rosa
-
Bauxite
Laterite
 RUDYTES:
 Breccia: Breccia is a mechanically formed sedimentary rock
which consists of angular fragments of heterogeneous
composition embedded in a fine matrix of cement. The
fragments are generally greater than 2mm in diameter. They
are of various types:
 Basal Breccia: This is formed by sea water advancing over
a cherty region.
 Fault Breccia: This rock is formed by the cementation of
fragments formed due to the braking of rocks by the
process of faulting. Also called crush breccia. Sometimes
other tectonic processes like folding and intrusion may
also produce breccias; all these types are commonly known
termed as fault/tectonic breccias.
 Agglomeratic Breccia: They are those rudaceous rocks in
which the angular fragments are of volcanic origin.
 Conglomerate: These are sedimentary rocks of clastic nature
and consist of rounded pebbles, gravel, boulders etc.
cemented together. The consequent fragments range in size
from 2mm and above, and their roundness is indicative of the
fact that they have undergone a good deal of transport by
water whereby their original angularities have been removed.
The rounded fragments may be of any composition; they may be
mineral or rock fragments. Similarly, the cementing material
may be siliceous or calcareous in composition, or a mixture
of these. Various types of conglomerates are:
 Volcanic conglomerates: The fragments are of volcanic
origin (but have undergone transport before deposition).
 Basal conglomerates: The fragments were deposited by sea
waves during their advance over a subsiding land mass.
 Glacial conglomerate: The fragments are of glacial
origin.
 ARENITES:
 Sandstone: These are mechanically formed sedimentary rocks
which result from compaction and consolidation of sand beds.
The component grains are generally of a diameter between 2mm
and 1/16mm. Silica is always the dominant constituent in
sandstone. The types of sandstone are:
 Siliceous sandstone: The cementing material or matrix is
siliceous in character.
 Calcareous sandstone: The matrix is made up of carbonates
of Ca, Mg, etc.
 Argillaceous sandstone: They are generally soft in
nature, the matrix is clayey in character.
 Ferruginous sandstone: they contain cementing material of
ferruginous composition.
On the basis of mineralogical composition, the following
types are commonly recognised:
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



Arkoses: These are sandstone exceptionally rich in
feldspars. These are assumed to have been derived from
granitic parent rocks.
Greywackes: These are impure sandstones of grey
appearance and contain quartz, feldspars and bits of
rocks like granites, feldsite, shales, etc.
Flagstones: These are sandstones rich in mica. Sometimes
mica flakes are present in parallel or sub-parallel
positions, resulting in the stone becoming weak in these
directions.
Freestones: They are massive sandstones that contain no
or very little divisional planes, assuming on the whole a
compact character.
 LUTITES:
 Shale: This is a fine-grained sedimentary rock of
argillaceous(clayey) composition. Shales are generally
characterised by a distinct fissility (property of easy
partition) parallel to he bedding and are made up of fine
clay particles of 1/256mm diameter. They are composed of
minute particles of uncertain composition; clayey minerals
like illite, montmorillonite and kaolin are generally
present. Montmorillonite and kaolin are invariable the chief
constituents. The types of shale are:
 Calcareous shale: They contain certain carbonates.
 Carbonaceous shale: These rocks are rich in organic
matter, especially carbon and are generally black.
 Alum shales: They are rich in iron sulphide (pyrites) or
sulphate.
 Oil shale: They are carbonaceous shales that yield oil on
destructive distillation.
NON-CLASTIC/CHEMICAL/NON-DETRITAL ROCKS:
 CARBONATE ROCKS:
 Limestone: Limestones are very important and widespread
sedimentary rocks that have formed from chemical as well as
organic processes. Pure limestones are chiefly composed of
calcite, whereas in common limestones, impurities like
clays, feldspars, quartz and pyrite may be present in
considerable amounts. Magnesium carbonate is generally a
common impurity. In some limestones, the magnesium
carbonates predominate, and he rock is called DOLOMITE. The
various types of limestone are:
 Chalk: It is he purest form of limestone, characterised
by fine-grained, earthy texture. The common colour is
white; some chalks may be exceptionally rich in the
remains of very small organisms like foraminifera.
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




Argillaceous Limestones: They are those in which clay is
present in considerable proportions. When carbonate and
clay are present in equal proportions, the rock is called
MARL.
Shell/Fossiliferous Limestone: The remains of some
organisms are preserved as fossils in the rock. When the
limestone is composed largely of shells and shell
fragments, it is called COQUINA.
Lithographic Limestones: They are compact, homogeneous
and extremely fine-grained calcareous rocks.
Kankar: It is a nodular or concretionary form of
carbonate formed by evaporation of subsoil water (rich in
CACO3) just near the surface.
Calc-sinter: It is a carbonate-rich deposit formed by
precipitation from carbonate-rich spring waters. These
deposits are also known as travertine or calc-tuff.
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