Rock types in India

1
INDIA- ROCK TYPES
By
PROF.A.BALASUBRAMANIAN
Centre for Advanced Studies in Earth Science,
University of Mysore,
Mysore-6

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Introduction:
The resources pertaining to rocks and
minerals are important components of land
resources of the country.
Mining in India is an important economic
activity which contributes very significantly
to the national economy.
Mining Industry is also a much profitable
industry today.

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Increasing industrial activities continue to
demand production of more minerals,
mineral fuels, oil and other geological
resources. Minerals which are essential raw
materials for manufacture of metals
witnessed an increasing demand and price
realization. Almost all the countries in the
world are endowed with some minerals. In
some countries, these resources may be
plenty while in some others such resources
may be scarce. The rock types are the bases.

4
The mining sector underwent much
modernization following the independence
of India although minerals have been mined
in the region since antiquity.
The country exports a variety of minerals—
found in abundance its geographically
diverse regions—while it imports others not
found in sufficient quantities within its
geographical boundaries.

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Rocks found in India:
Rocks found in India are classified into three
broad categories, viz. igneous, sedimentary
and metamorphic rocks.
Their occurrences vary from widespread
stretches to small patches or pockets
throughout the country. The distribution of
various rocks are to be studied in geography.

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This report highlights the following:
1) Different Kinds of Rocks
2) Distribution of Igneous Rocks
3) Distribution of Sedimentary Rocks
4) Distribution of Metamorphic Rocks
5 ) Distribution of Different Kinds of Rocks.

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1) DIFFERENT KINDS OF ROCKS:
Let us understand the names of rocks.
Igneous Rocks:
These are the primary rocks or the first
formed rocks. The very important rocks of
this category are:
Andesite is an Intermediate volcanic rock.
Anorthosites are igneous ultramafic rocks
composed predominantly of plagioclase.

8
Aplite is a very fine grained intrusive
igneous rock.
Basalt is a major volcanic rock of mafic
composition.
Basanite a volcanic rock of mafic
composition; essentially a silica
undersaturated basalt.
Carbonatite a rare igneous rock composed
of >50% carbonate minerals.
Charnockite is a rare type of granite
containing pyroxene.

9
Enderbite is a variety of charnockite.
Dacite is a felsic to intermediate volcanic
rock with high iron content.
Diabase or dolerite is an intrusive mafic
rock forming dykes or sills.
Diorite is a coarse grained intermediate
plutonic rock composed of plagioclase,
pyroxene and/or amphibole.
Dunite is an ultramafic cumulate rock
composed of olivine and accessories.

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Essexite is a silica undersaturated mafic
plutonic rock (essentially a foid-bearing
gabbro).
Gabbro is a coarse grained plutonic rock
composed of pyroxene and plagioclase
basically equivalent to basalt.
Granite is a coarse grained plutonic rock
composed of orthoclase, plagioclase and
quartz.
Granodiorite is a granitic plutonic rock with
plagioclase > orthoclase.

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Granophyre is a subvolcanic intrusive rock
of granitic composition.
Hornblendite is a mafic or ultramafic
cumulate rock dominated by >90%
hornblende.
Ignimbrite is a fragmental volcanic rock.
Ijolite is a very rare silica-undersaturated
plutonic rock.
Kimberlite is a rare ultramafic, ultrapotassic
volcanic rock and a source of diamonds

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Komatiite is an ancient ultramafic volcanic
rock.
Lamprophyre is an ultramafic, ultrapotassic
intrusive rock dominated by mafic minerals.
Monzonite is a plutonic rock with <5%
normative quartz.
Nepheline syenite is a silica undersaturated
plutonic rock with nepheline replacing
orthoclase.
Nephelinite is a silica undersaturated
plutonic rock with >90% nepheline.

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Norite is a hypersthene bearing gabbro.
Obsidian is a type of volcanic glass.
Pegmatite is an igneous rock (or
metamorphic rock) with giant sized crystals
Peridotite is a plutonic or cumulate
ultramafic rock composed of >90% olivine.
Phonolite is a silica undersaturated volcanic
rock; essentially similar to nepheline
syenite.
Picrite is an olivine-bearing basalt.

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Porphyry is a rock, usually granitic, with a
porphyritic texture.
Pumice is a fine grained, extremely
vesicular volcanic rock.
Pyroxenite is a coarse grained plutonic rock
composed of >90% pyroxene
Quartz diorite is a diorite with >5% modal
quartz.
Quartz monzonite is an intermediate
plutonic rock, essentially a monzonite with
5-10% modal quartz.

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Rhyodacite is a felsic volcanic rock which is
intermediate between a rhyolite and a dacite.
Rhyolite is a felsic volcanic rock .
Scoria is an extremely vesicular mafic
volcanic rock.
Syenite is a plutonic rock dominated by
orthoclase feldspar; a type of granitoid.
Tachylyte is essentially a basaltic glass.
Tephrite is a silica undersaturated volcanic
rock; can be a generic term.
Tonalite is a plagioclase-dominant granitoid.

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Trachyte is a silica undersaturated volcanic
rock; essentially a feldspathoid-bearing
rhyolite.
Tuff is a fine grained volcanic rock formed
from volcanic ash.
Websterite is a type of pyroxenite,
composed of clinoproxene and
orthopyroxene.

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The Sedimentary rocks:
These are secondary rocks formed through
processes of sedimentation and subsequent
modification.
The important rocks of this category are:
Anthracite is a type of coal.
Argillite is a sedimentary rock composed
primarily of clay-sized particles.

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Arkose is a sedimentary rock similar to
sandstone.
Banded iron formation is a fine grained
chemical sedimentary rock composed of
iron oxide minerals.
Breccia is a sedimentary or tectonic rock
composed of fragments of other, broken
rocks.
Cataclasite is a rock formed by faulting.
Chalk is a sedimentary rock composed
primarily of coccolith fossils.

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Chert is a fine grained chemical sedimentary
rock composed of silica.
Claystone is a sedimentary rock formed
from clay.
Coal is a sedimentary rock formed from
organic matter.
Conglomerate is a sedimentary rock
composed of large rounded fragments of
other rocks.
Diamictite is a poorly sorted conglomerate.

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Coquina is a sedimentary carbonate rock
formed by accumulation of abundant shell
fossils and fragments.
Diatomite is a sedimentary rock formed
from diatom fossils.
Dolomite or dolostone is a carbonate rock
composed of the mineral dolomite +/-
calcite.
Evaporite is a chemical sedimentary rock
formed by accumulation of minerals after
evaporation.

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Flint is a form of chert.
Greywacke is an immature sandstone with
quartz, feldspar and rock fragments within a
clay matrix.
Gritstone is essentially a coarse sandstone
formed from small pebbles.
Laterite is a residual sedimentary rock
formed from a parent rock under tropical
conditions.

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Lignite is a sedimentary rock composed of
organic material; otherwise known as Brown
Coal.
Limestone is a sedimentary rock composed
primarily of carbonate minerals.
Marl is a limestone with a considerable
proportion of silicate material.
Mudstone is a sedimentary rock composed
of clay and mud.
Oil shale is a sedimentary rock composed
dominantly of organic material

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Oolite is a chemical sedimentary limestone.
Sandstone is a clastic sedimentary rock
defined by its grain size.
Shale is a clastic sedimentary rock defined
by its grain size.
Siltstone is a clastic sedimentary rock
defined by its grain size.
Travertine is a sedimentary rock containing
calcite and iron oxides.

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Turbidite is a particular sequence of
sedimentary rocks which form within the
deep ocean environment.
Metamorphic Rocks
Amphibolite is a metamorphic rock
composed primarily of amphibole.
Blueschist is a metamorphic rock composed
of sodic amphiboles with a distinct blue
color.

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Phyllite is Banded gneiss with a dike of
granite orthogneiss.
Eclogite is an ultra-high grade
metamorphosed basalt or gabbro; also a
facies of metamorphic rocks.
Gneiss is a coarse grained metamorphic
rock.
Gossan is the product of the weathering of a
sulfide rock or ore body.

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Granulite is a high grade metamorphic rock
formed from basalt; also a facies of
metamorphic rocks.
Greenschist is a generic term for a mafic
metamorphic rock dominated by green
amphiboles-Greenstone.
Hornfels is a metamorphic rock formed by
heating by an igneous rock.
Marble is a metamorphosed limestone.
Migmatite is a high grade metamorphic rock
verging upon melting into a magma.

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Mylonite is a metamorphic rock formed by
shearing.
Pelite is a metamorphic rock with a
protolith of clay-rich (siltstone) sedimentary
rock.
Phyllite is a low grade metamorphic rock
composed mostly of micaceous minerals
Psammite is a metamorphic rock with a
protolith of quartz-rich (sandstone)
sedimentary rock.

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Pseudotachylite is a glass formed by
melting within a fault via friction.
Quartzite is a metamorphosed sandstone
typically composed of >95% quartz.
Schist is a low to medium grade
metamorphic rock.
Serpentinite is a metamorphosed ultramafic
rock dominated by serpentine minerals
Skarn is a metasomatic rock.
Slate is a low grade metamorphic rock
formed from shale or silts.

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Soapstone is essentially a talc schist.
Specific Varieties of Rocks:
These are specific classes of rocks, or
altered products of existing rocks.
Adamellite is a variety of quartz monzonite.
Aphanite is an aphanitic felsic volcanic rock
which confounds identification via optical
means.
Blue Granite is essentially larvikite, a
monzonite.

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Felsite is an aphanitic felsic volcanic rock
which confounds identification via optical
means.
Flint is typically a form of chert, jasper, or
tuff.
Jadeitite is a very rare rock formed by
concentration of jadeite pyroxene; a form of
serpentinite
Jasperoid is a hematite-silica metasomatite
analogous to a skarn.

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Luxullianite is a tourmaline-bearing granite
with a peculiar texture.
Pyrolite is a chemical analogue considered
to theoretically represent the earth's upper
mantle.
Rapakivi granite is a granite which exhibits
the peculiar rapakivi texture.
Rhomb porphyry is a type of latite with
euhedral rhombic phenocrysts of feldspar.

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Shonkinite is an archaic and informal term
used to describe melitilic and kalsititic
rocks; often used today.
Taconite is a term for banded iron formation
primarily used in industries.
Teschenite is essentially a silica
undersaturated, analcime bearing gabbro.
Theralite is essentially a nepheline gabbro.
Variolite is devitrified glass.

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Legend and symbols used in the maps used
for explanation.
The Map prepared by the Govt. of India,
Survey of India, has been considered in this
report.

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2) DISTRIBUTION OF IGNEOUS
ROCKS
Igneous rocks are primary rocks produced
by magmatic processes. They are formed
from the cooling of molten masses. They
may be either intrusive or effusive in nature.
Intrusive igneous rocks are those rocks
which have been forced, while in a plastic or
liquid state, into the cavities or cracks or
between the layers of other rocks.

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In India, granite, grano-diorite and
pegmatite appear as intrusive igneous rocks
and they occur extensively both in
peninsular as well as in the Himalayan
region.
They exist as a big chunk in Bundelkhand
upland and a slightly smaller patch in
eastern most part of Maharashtra plateau.

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This may be regarded as a granite intruded
into older gneisses, large patches of which
have remolted.

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It is traversed by extensive dykes and sills of
a coarse grained diorite, which persists for
long distances. It is also traversed by a large
number of coarse pegmatite veins as in a
boss of granite. They intersect the drainage
course of the region and causes numerous
small lakes which are typical of
Bundelkhand upland. Identical rock
formation occur in Kashmir Himalayas
where they are widespread in parallel
congregation, running from NW to SE.

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The main crystalline development is in the
Zaskar Range and also in Ladakh and
Karakoram ranges.

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The core of the Dhauladhar range is formed
of these rocks but in Pir Panjal range they
occur only in a number of minor intrusions.

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Their appearance is also observed in the
northeastern corner at Soda plain.
They are scattered elsewhere like north
eastern corner of India, southwestern and
southern part of Aravalli range, outer part of
Mishmi hill, etc.
Another important north-south elongation of
south rocks is found along Karnataka
plateau stretching from Bellary and reaching
upto Mysore.

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Gabbro-anorthosites are also intrusive
igneous rocks located in small pockets like
westernmost part of Manipur, Upper
Damodar valley as same where else.
Effusive igneous rocks appearing as basalt,
associated lavas and tuff are found in the
Deccan lava region stretching from Malwa
plateau in the north and covering entire
Maharashtra plateau in the south.

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They are extended in places like Kathiawar
peninsula, along interior Kachchh peninsula,
Mahadeo range, Maikal range, Rajmahal
hills, small pockts in Meghalaya, Dihang
(middle) basin, Kashmir Himalayas along
Pir Panjal range, scattered in places of
Marusthali, Rajasthan Bagar and elsewhere
in central India.

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Deccan lava, traditionally known as Deccan
Trap, occupies an area of 5,18,000 km2
with
a thickness ranging between 600 and
1,500m which reaches a maximum of
3,000m along the coast of Bombay.
These are practically horizontal and
remarkably homogeneous basalts,
representing mesa-like terrain, and were
probably extruded from fissures towards the
end of the Cretaceous era.

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Characteristic denudation has resulted
cutting through the basalts and detaching a
number of outliers, seperated from the main
area by wide distances.
The basalts are largely used as road metals,
public works, building stones in dwellings,
etc. Decomposed basalts produce soils,
which appear as highly argillaceous dark
loam and contain calcium, magnesium,
carbonates, potash, phosphates, etc.

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They are considered as rich agricultural
soils.
Much of the well-known “cotton soil”,
known as the “black soil” or regur, is due to
the subaerial weathering of the basalts in
situ and a subsequent admixture of the
weathered products with iron and organic
matter.
Rhyolite, the other effusive igneous rocks is
of minor importance.

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They are found scattered in places of
Marusthali, Rajasthan Bagar and elsewhere.
3) DISTRIBUTION SEDIMENTARY
ROCKS
Rocks composed of sediments are known as
sedimentary rocks. Two broad groups within
such rocks are unconsolidated and
consolidated sedimentary rocks.

53
In India sedimentary rocks are found
extensively along North Indian plains
stretching from Marusthali in the
westernmost border to Brahmaputra valley
in the east.
Recent alluvium, older alluvium, blown
sand and laterites belong to the
unconsolidated sedimentary formation.
Entire north Indian plain is overlain by
alluvium deposited during recent geological
era.

54
They are spread over Indo Gangetic-
Brahmaputra valley region. These alluvial
deposits are so thick that hardly the bed rock
has been reached.
It is considered that the Indo-Gangetic
depression is a “force-deep”, a down trap of
the Himalayan foreland, of varying depth,
converted into flat plains by the simple
process of alluviation.

55
So far, as the exact depth of the alluvium is
concerned, the same has not yet been
ascertained. However, gravity, magnetic,
and seismic exploration reveal the fact that
the thickness varies from place to place,
which ranges form 1,000 to over 2,000m.
The area of these alluvial plains is 7,75,000
km2
• In width they vary from a maximum of
500 km in the western part to less than 150
km in the east.

56
Recent alluvium has also been developed
along coastal plains, both to the east as well
as to the west, particularly in delta regions
formed by major rivers of the Ganga,
Mahanadi, Godavari, Krishna, Cauvery, etc.
Long stretches of such alluvial deposits are
found along Narmada, Tapti, Chambal and
Jhelum basins.

57
Older alluvium have been developed in
narrow patches along edges of recent
alluvium. They are more pronounced in the
foothill region of eastern Himalayas caused
by alluvial fan development. They are also
noticed along outer Jhelum basin.
Although the alluvial plains are devoid of
mineral resources, yet they are the highest
economic asset of India because of their
contribution in agricultural production.

58
Moreover, clays are used for earthenwares
and also for brick making - which is
considered as an important building
material throughout the plains. Kankar is
used for lime and cement making and also
for road construction.
The alluvial plains are also considered as
the store house of extensive sweet water,
available either on the surface or confined
within underground aquifers.

59
Westernmost part of India is covered by
blown sand resulted from aeolian
accumulations.
This is the typical desert region known as
the Thar, which stretches form west of the
Aravallis to the Indus basin. Its north-south
extension lies between the Punjab plains,
the Satluj basin and almost 25° N latitude.
It occupies an area of 650 km in length and
150 km in width.

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In these deserts the predominant
components of the sand are well -rounded
grains of quartz alongwith feldspar and
hornblende grains.
Laterites are also considered a~ older
alluvium. They are the typical formations
of Rarh plains of West Bengal which are
mostly confined within western districts.
They stretch from Murshidabad district in
the north to Medinipur district in the south.

61
They are also found around Jabalpur pats,
in long stretches along coastal Tamil Nadu
and around Vishakhapatnam and south of
Ongole of Andhra Pradesh.
Small pockets within Marusthali and
around Bidar also exhibit such formations.
Sandstone, shale, conglomerate and
limestone are the major formations within
consolidated sedimentary rocks.
They appear either exclusively or are
associated with other rocks.

62
Sandstones are found in small pockets in
coastal plains of Tamil Nadu.
Sandstone and shale occupy places in
middle Vaigai valley, wide stretch along
Godavari valley,
large areas around Rann of Kachchh,
Kashmir Himalaya,
North-Eastern hill states (particularly in
Mizo hills Manipur hills,
Barail range, long stretches in Nagaland ),
Narmada valley,

63
middle Mahanadi valley,
Chambal valley, Chittaurgarh (Rajasthan),
Son valley (Mirzapur), Eastern Himalayan
foothills etc.
Sandstone, shale, limestone occur
extensively around Jaisalmer and also in
Kachchh penisula. They are found in
Nicobar Islands as well.
On the other hand, sandstone, shale,
conglomerate are found along western parts-
of the Siwaliks.

64
Andaman Islands are also mostly covered by
identical types of rocks. Sandstone and
quartzite are the typical formations of
middle Godavari valley around Chandrapur.
Shale is another important consolidated
sedimentary rock which occur either
exclusively or in association with sandstone
or phyllite.
Shale as such is found in small patches in
central India, particularly across Godavari
basin.

65
Shale, associated with sandstone, are found
along Narmada valley near Hoshangabad
and between Sonpahar and Maikal range in
Son valley.
Shale, phyllite combination occur in
southern part of Chotanagpur plateau (south
of Chaibasa).
Conglomerates are generally assoclated with
clay and are found in westernmost part of
Medinipur district of West Bengal.

66
Exclusive limestone formation can be traced
in the Himalayas located to the northern part
of Almora, whereas limestone, shale
combination are found extensively in the
Himalayas, particularly in Ladakh plateau
(Kargil), northernmost part of Kashmir,
Badrinath area, etc.
The latter also occur in central India (Durg-
Raipur-Bilaspur area) and southern India
(around Nandyal valley).

67
Limestone, slate combination are found in
isolated patches in Kashmir Himalayas.
Limestone, shale or slate, sandstone or
quartzite combination occur in northern
Ladakh near Karakoram pass and also along
Zaskar range.

68
4) DISTRIBUTION OF METAMORPHIC
ROCKS
Metamorphic rocks are such rocks which
have undergone pronounced alteration by
heat, pressure, water or any combination of
these since the rocks were formed.
Thus, granite may have its principal crystals
separated and arranged in crude layers to
form Gneiss.

69
Limestone may be recrystallised to marble
or excessive pressure may transform shale
into slate.
However, compared with other two types of
rocks, occurrence of metamorphic rocks is
of less significance in India.
Quartzites are found scattered all along
Aravalli ranges.
A big chunk of such formation can be traced
in the Dandakaranya region.

70
Quartzite, Limestone formations occur in the
Himalayas along Almora-Pithorgarh region
and also along Nag-Tibba range.
In the south they are found in the western
part of Nandyel valley.
Quartzite and shale occurences are mostly
confined within central India.
They occur in places like southern part of
Bundelkhand upland, upper catchment area
of Mahanadi basin, along Hirakud basin and
also around Gwalior.

71
Quartzite, schists are widespread in northern
part of Hazaribagh plateau, along Rajhara
Pahar and also around Parasgaon.
Quarzite, slate, phyllite, limestone are more
pronounced as big chunk in Bastar,
particularly around Jagdalpur.
Quarzite and phyllite are scattered in parts
of Dandakaranya. They also occur in upper
reaches of Narmada valley.

72
Exclusive slate occurrence is found in the
eastern part of Telangana plateau, slate,
quartzite formations are widespread in
Kashmir Himalayas.
They also occur in Kumaun Himalayas.
Identical formations may be traced in
sizeable patch in the Eastern Ghats
particularly to the western part-of Kallamala
range.

73
Slate, phyllite, schists are confined in the
northern part of Sikkim.
Slate, quartzite, schist are found in the
southern Son valley as well as in Himachal
Pradesh (north of Nahan).
Schists are more pronounced in southern
India, particularly along eastern part of
Kallamala range, south of Kolar, around
Raichur and also across Tungabhadra valley.

74
Schists, phyllite, slate, quartzite combination
are found along a wide stretch in Arunachal
Pradesh.
Otherwise they occur in the western part of
Shillong plateau, along Sundargarh -
Raigarh-Chaibasa sector.
They are also scattered along Aravalli range.
Schists, slate, conglomerate combinations
are confined within small pockets located to
the south of Mahanadi basin (south of
Raigarh).

75
Schists/ phyllite, limestones/marble,
amphibolite combination are found in
northern Wainganga basin.
Schists, gneisses, quartzite or banded
hematite, are widespread in Karnataka
plateau.
Schists and gneisses are confined within
small pockets in the central India (south of
Mandla).

76
Other Igneous and Metamorphic Rocks
Khondolite and charnokite are the important
formation included within this group of
rocks.
The former is widespread in southern India,
particularly along Eastern Ghats (north of
Godavari delta) and also Western Ghats
(southern part of Kerala).

77
The latter formations are scattered in
different places of southern India, e.g.
interior parts of Kerala, Karnataka, Andhra
Pradesh; Tamil Nadu (south of Madras), etc.
Metabasic and ultrabasic rocks, epiodiorite
or ophiolite are found scattered both in
northern India as well as in central India.

78
In the north, they are confined in small
pockets in western Himalayas, whereas such
rocks are found scattered on central India,
particularly in
Chotanagpur plateau,
eastern part of Rajhara Pahar,
Simlipal massif (near Baripada), etc.

79
Magnetite or lime silicic rocks are found in
western Himalayas (Uttar Pradesh,
Himachal Pradesh and Kashmir), whereas
unclassified crystalline rocks (mainly
gneisses) are very much widespread in
southern and central India.
They also occur in eastern India, especially
in Meghalaya, Mikir hills, Chotanagpur
plateau, etc. as well as western India in the
Aravallis.

Rock types in India

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