CLASSIFICATION OF ROCKS ON THE BASIS OF MODE OF FORMATION ROCKS ARE CLASSIFIED INTO THREE CATEGORIES 1 IGNEOUS ROCKS 2 SEDIMENTARY ROCKS 3 METAMORPHIC ROCKS ROCKS IGNEOUS ROCKS IGNEOUS ROCKS ALSO KNOWN AS PRIMARY ROCKS ARE FORMED BY SOLIDIFIC ID: 1018342
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1. ROCK IS AN AGGREGATE OF MINERALS.ROCK HAS BEEN DEFINED AS COHERENT,CONSOLIDATED AND COMPACT MASS OF TWO OR MORE THAN TWO MINERALS.CLASSIFICATION OF ROCKS:ON THE BASIS OF MODE OF FORMATION ROCKS ARE CLASSIFIED INTO THREE CATEGORIES:1 IGNEOUS ROCKS2 SEDIMENTARY ROCKS3 METAMORPHIC ROCKS ROCKS
2. IGNEOUS ROCKS: IGNEOUS ROCKS, ALSO KNOWN AS PRIMARY ROCKS ARE FORMED BY SOLIDIFICATION OF MAGMA. MAGMA IS MOLTEN ROCK MATERIAL CONSISTING OF LIQUID,GAS AND CRYSTAL.IGNEOUS ROCKS ARE RECODS OF THERMAL HISTORY OF EARTH.GRANITE IS THE MOST COMMON VARIETY OF IGNEOUS ROCK AND IS TYPICALLY EXPOSED IN ERODED MOUNTAIN BELTS AND IN ROOTS OF ANCIENT MOUNTAINS. BEST EXAMPLE OF IGNEOUS ACTIVITY IS VOLCANIC ERUPTION.
3. TYPES OF IGNEOUS ROCKS:1 INTRUSIVE IGNEOUS ROCKS2 EXTRUSIVE IGNEOUS ROCKS INTRUSIVE IGNEOUS ROCKS:ON THE BASIS OF DEPTH AND PLACE OF COOLING OF MAGMA,THESE ROCKS ARE SUB-DIVIDED INTO TWO TYPES
4. A) PLUTONIC – igneous rocks of deep seated origin are known as plutonic rocks.granite, diorite, gabbro the examples of plutonic rocks.The largest partially exposed is batholith. B ) HYPABYSSAL -these rocks are formed due to cooling and solidification of magma just beneath the earth s surface.
5. a) -BATHOLITH:The term applies to any large intrusive mass of igneous rock (almost always granite) I which there is no observable bottom.A batholith generally covers more than 100 sq. kms.b) LACCOLITH – It is an intrusive dome like mass of igneous rock.They can be several kilometres in diameter,thousands of metres thick.
6. c) SILL- a sill is a sheet like body of igneous rock .it is a tabular body of intrusive rocks injected between layers of enclosing rocks.d) STOCK It is intrusive mass of rock with an outcrop of fewer than 10 sq. kms.Some stocks are known to be small protrusions rising from the main batholith.stocks are generally formed of granite. Many deposits of gold ,silver, lead , zinc and copper are deposited in fractures and form veins from a stock into the surrounding rock.
7. e) dyke – a dike is a sheet like body of intrusive igneous rock which rise upward from a magma chamber and cuts discordantly through the bedding plane of country rock .its thickness may vary from cms. to hundreds of metres f) phacolith – a concave- convex body of igneous form which is anticinal in form .They range in size from a few metres to a few kilometres
8. EXTRUSIVE IGNEOUS ROCKS rocks formed by solidification of magma above the earth s surface are known as extrusive igneous rocks.in other words these rocks are formed from magma extruded onto earth s surface by volcanic erruptions.the volcanic lava is an example of extrusive rock.
9. MAJOR CHARACTERISTICS OF IGNEOUS ROCKSThese rocks are solidified from a molten magma.These rocks do not occur in distinct beds.These rocks are not fossiliferous.These rocks are hard and water percolates in them with great difficulty along the joints.These rocks are less affected by chemical weatheringThese rocks are granular and crystalline.Valuable minerals like iron ore , gold, silver, copper, tin, mica ,aluminium etc.are found in igneous rocks.Igneous rocks are generally associated with volcanic activity.