MINERALS AND
In geology
rocks is the naturally occurring aggregate that consist of one or two minerals.
Example :-
the common rock granite is the combination of quartz , feldspar and biotite
minerals. Most rocks consist of polyminerals.
CLASSIFICATION
OF ROCKS
On the
basis of origin rocks are mainly classified into three major groups :
1- Igneous rocks
2- Sedimentary rocks
3- Metamorphic rocks
IGNEOUS ROCKS
Mainly
these rocks are massive in form and it is supposed that these rocks are the
oldest , ones formed on the earth crust
these rocks also known as the primary rocks.
Examples of
the Igneous rocks :-
Granite ,
gabbro , are formed by the solidification of magma.
Basalt are
formed due to solidification of lava.
CLASSIFICATION
OF IGNEOUS ROCK
1- EXTRUSIVE ROCK
2- INTRUSIVE ROCK
EXTRUSIVE
ROCK : An extrusive igneous rock forms when magma erupt and solidifies on the
earth surface. Because of extrusive rocks are so commonly associated with
volcanoes , they are also called volcanic rocks.
The texture
of these rocks is fined grained texture. E.g. Basalt
INTRUSIVE
ROCK : An intrusive igneous rock forms when magma crystallized within the crust
. Depending upon the depth of formation , the intrusive rocks are classified
into plutonic rocks and hypabyssal rocks.
PLUTONIC
ROCK :- the rock formed at greater depth are called plutonic rocks. The texture
of these rocks is coarse grained texture.
For example
– granite , gabbros rocks
HYPABYSSAL
ROCKS :- the rock formed at depth close to the crust are called as hypabyssal
rocks. Hybabassal igeneous rocks are formed between the plutonic and volcanic
rocks . These are common than the plutonic or volcanic rocks and do often forms
dikes , sills ,laccoliths , dolerites , rocks .
The texture
of these rocks is finer than the plutonic and finer coarse grained than the
volcanic rocks.
VARIOUS FORMS OF THE IGNEOUS ROCKS
1- DYKES
2- SILLS
3- LACCOLITHS
4- LOPOLITHS
5- PHACOLITHS
TEXTURES OF IGENEOUS ROCKS
1- EQUIGRANULAR
2- INEQUIGRANULAR
3- DIRECTIVE TEXTURE
4- INTERGROWTH TEXTURE
5- INTERGRANULAR TEXTURE
SEDIMENTARY ROCKS
The are the
types rocks which are formed by the deposition of material at the earth’s
surface and within bodies of water.
Sedimentation
is the collective name for the processes that cause minerals or organic
materials to settle and accumulate or minerals to precipitation from their
solution.
CLASSIFICATION OF THE SEDIMENTARY ROCKS
1- Classification based on the presence
of the sediment of particle grain size ;-
a- RUDACEOS ROCK : The rocks that
consist of coarse grains whose size is more than 2 mm heterogeneous composition
is called Rudaceous rock. These are also called rudites or phephites. Breccias
and conglomerates are the important rocks.
b- ARENAEOUS ROCK : the rocks which
consist of grains size 1/16 to 2 mm are called arenaceous rocks . these are
also called arenites or psammites. Sandstone and greywacke are the examples of
these rocks.
c- ARGILLACEOUS ROCKS :- the rocks
which include all the finest sediments of size less than 1/16 are called
aregillaceous rocks. These are also called as the pelites. Silt , clay shale and
mudstone are the important rocks.
2- On the basis of chemical composition
of the sedimentary rocks :-
a- SILICEOUS ROCK :- these sedimentary
rocks contain silica as main constituents.
b- CARBONATE ROCKS :- carbonate
sedimentary rocks are precipitate from the carbonate rich water under different
condition , controlled by the concentration of the carbon dioxide. For example
: carbonate deposite of iron , limestone , dolomite
c- FERRUGENOUS ROCKS :- These sediment
rocks formed by the precipitation of iron oxides. For example :- Haematite ,
pyrite , iron stone.
d- EVAPORITES :- These sedimentary
rocks are formed by evaporation of saline lakes . for example Gypsum , rock
salt , borates
3- On the basis of the organically formed
sedimentary rocks ;-
a- BIOCHEMICAL ROCKS : The biochemical
sediments are produced when plants and animals living under water , extrude
from it dissolves minerals matter , usually calcite , to form shells or other
hard parts . These shells accumulate on the ocean in great quantities to form
sedimentary rocks. For example :- shell limestone
b- ORGANIC ROCKS :- The sedimentation
rocks are formed due to sedimentation and decomposition of vegetation matter is
known as organic rocks . For example :- peat , lignite , coal
METAMORPHIC ROCKS
These are
arise from the transformation of existing rock types in a process called
metamorphism which means “change in form” .
Metamorphic
rocks are formed by the physical and chemical alternation of heat and pressure
of an existing igneous or sedimentary material into a denser form .
AGENTS OF THE PROCESS METAMORPHISM
1- Chemical activity as a metamorphic
agent
2- Heat as a metamorphic agent
3- Pressure and stress as the
metamorphic agent
TEXTURE OF THE METAMORPHIC ROCKS
1- CRYATALLOGRAPHIC TEXTURE
2- PORPHYROBLASTIC TEXTURE
3- BLASTO- PORPHYRITIC TEXTURE
4- BLASTOPHYTIC TEXTURE
5- XENOBLASTIC TEXTURE
6- GRANOBLASTIC TEXTURE
STRUCTURE OF METAMORPHIC ROCKS
1- Cataclastic structure
2- Schistose structure
3- Gneissose structure
4- Maculose structure
5- Granulose structure
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