Rocks are huge mass substance that are formed inside the earth’s crust due to rapid heating and cooling of lava. Rocks do not have any specific shape or chemical composition but are mixtures of two or more minerals. The rocks are classified into three groups i.e. Geological, Physical and Chemical classification.
In this article, classification and types of rocks shall be discussed.
Classification of rocks :
Geological Classification :
1. Igneous Rocks : These rocks are formed by the solidification of molten material within earth’s crust called magma. The temperature of magma ranges from 5000to 14000C. Lava after cooling becomes rock after emerging out of earth’s surface is called Extrusive Igneous Rock and formed within earth’s crust is called Intrusive Igneous Rock.
Examples –Granite, Basalt, Dolerite.
2. Sedimentary Rocks : These rocks are formed by weathering action of water, wind, frost, intense heat subjected to movement by various agencies like wind, water, ice and are ultimately deposited at favourable place and form rock.
Example –Limestone, Sandstone, Laterite, Dolomite, Conglomerate, Shale, Gypsum.
3. Metamorphic Rocks : These rocks are formed at great depths under the action of severe heat and pressure on igneous or sedimentary rocks.
Example –Marble, Quartzite, Gneiss, Slate.
Physical Classification :
1. Stratified Rocks : Stratified Rocks are those rocks which show planes of cleavage (exhibit distinct layers) along which they can be easily split.
Example – Limestone and Sandstone.
2. Unstratified Rocks : Unstratified Rocks are those rocks which do not have strata or separate layers. These rocks cannot be split into separate slabs.
Example –Granite and Marble.
3. Foliated Rocks : Foliated Rocks are those rocks which show parallel layers of platy minerals like mica bands of different minerals between them.
Chemical Classification :
1. Silicious Rocks : Silicious Rocks contain silica as main constituent. These rocks are strong, hard and resist weathering action.
Example –Granite, Sandstone, Gneiss.
2. Argillaceous Rocks : Argillaceous Rocks contain alumina as main constituent. These rocks are strong, hard but are generally brittle.
Example –Slate, Laterite.
3. Calcarcous Rocks : Calcarcous Rocks contain calcium carbonate as main constituent. Durability of these rocks depend on surrounding atmosphere.
Example –Marble, Limestone.
Types of Rocks :
1. Granite :
i) Granite is an igneous rock essentially consisting of feldspar, quartz and mica. It is an excellent building material because of good appearance, great strength, high resistance to weathering and high compressive strength.
ii) Crushing Strength = 100 – 150 N/mm2.
iii) Uses – Steps, facing work, walls, floor.
iv) Found in India – Assam, Bengal, Bihar, Gujarat, Karnataka, Kashmir, Maharastra and Tamil Nadu.
2. Basalt :
i) Basalt is an igneous rock which is very tough and hard and does not allow itself to be easily worked.
ii) Uses – Foundation work, rubble masonry and as road metal.
iii) Found in India – Bengal, Bihar, Gujarat, Madhya Pradesh and Maharastra.
3. Gneiss :
i) Gneiss is a metamorphic rock and allows itself to split into slabs.
ii) Uses – Rough masonry works.
iii) Found in India – Andhra Pradesh, Bengal, Bihar, Gujarat, Karnataka, Kerala, Maharashtra and Tamil Nadu.
4. Laterite :
i) Laterite is a metamorphic rock having porous structure.
ii) Uses – Building stone, road metal and stone masonry work.
iii) Found in India – Andhra Pradesh, Bihar, Karnataka, Madhya Pradesh, Maharashtra and Kerala.
5. Lime Stone :
i) Lime stone is a sedimentary rock, main content being calcium carbonate.
ii) Uses – Roofing, paving, flooring and road metal.
iii) Found in India – Andhra Pradesh, Bengal, Bihar, Gujarat, Himachal Pradesh and Uttar Pradesh.
6. Marble :
i) Marble is a metamorphic rock and having mainly interlocking calcite grains. It allows itself to be carved and taken an excellent polish.
ii) Uses – Ornamental work, facing work and flooring.
iii) Found in India – Andhra Pradesh, Gujarat, Karnataka, Maharashtra, Rajasthan and Uttar Pradesh.
7. Sand Stone :
i) Sand stone is a sedimentary rock. It has uniform grains and is light in colour. It can be easily worked and dressed.
ii) Crushing Strength = 40 – 80 N/mm2.
iii) Uses – Facing work, floors and walls.
iv) Found in India – Andhra Pradesh, Bengal, Bihar, Himachal Pradesh, Gujarat, Maharashtra, Kashmir, Tamil Nadu, Uttar Pradesh ad Rajasthan.
8. Slate :
i) Slate is a metamorphic rock. It allows itself to be split along its bedding planes.
ii) Compressive strength = 70 – 200 N/mm2.
iii) Uses – Roofs and sills.
iv) Found in India – Bihar, Karnataka, Tamil Nadu and Madhya Pradesh.
