Building Material – Stone ! Classification of Stone/ Rock

Stone/Rocks are classified in the following three ways :

1) Geological Classification

2) Physical Classification

3) Chemical Classification

A) Geological Classification : Based of formation of Rocks & further classified three types :

i) Igneous Rock

ii) Sedimentary Rocks

iii) Metamorphic Rocks

i) Igneous Rocks :

The rocks formed directly by solidification of molten material , either on surface or the surface of earth called Igneous Rocks.

Ex : Granite, Basalt, Trap & Delorite.

Formation of Igneous Rocks :

At a certain depth , the temperature of material with in the earth’s crust become so high that the existing material may acquire a molten state is called Magma.

When the molten material out from earth called Lava. When the molten condition change due to temperature, pressure & chemical composition ) surrounding the magma, it changes into a solid state in the form of simple solid masses known as Igneous Rocks.

These rockes divided further three classes :

1. Plutonic Rocks
2. Hypabyssal Rocks
3. Volcanic Rocks

1. Plutonic Rocks : formed due to cooling of magma at a considerable depth from earth surface. The cooling is slow & the rock posses coarsely grained crystalline structure. Ex Granite.
2. Hypabyssal Rocks : these rocks are formed due to cooling of magma at a relatively shallow depth (2-3 KM) from the earth surface. The cooling is quick & possess finely grained crystalline structure. Ex. Delorite
3. Volcanic Rocks : Formed due to pouring of magma at a earth surface. The cooling is very rapid. Hence these rocks are extremely fine grains in structure.

They frequently contain some quantity of glass which is a non crystalline material. Ex. Basalt.

ii) Sedimentary Rocks / Stratified & Aqueous Rock  :

these formed by consolidation/break of particles of the pre- existing rocks, under the effect of weather agencies (ice,water, air, sun heat , gases etc) are called sedimentary rocks.

These are most widespread rocks found covering a great part of earth.

Ex. : Gravel, sandstone, lime stone, lignite etc.

Formation :

1. Disintegration of pre-existing rocks under the effect of weather agencies.
2. Transported by these natural agencies to river beds , lake basin, seas & ocean or in suspension to other place.
3. Setting down the suspended particles or precipitation of the soluble constituents.
4. Compaction and consolidation of the deposited sediments either due to pressure or chemical action like silica, lime ,iron etc.

Sedimentary following four types of deposit occurs :

A) Residual Deposits

B) Sedimentary Deposits

C) Chemical Deposits

D) Organic Deposits

Residual Deposit : Some portion of product of weathering remain at the site of origin known as Residual Deposits.

Sedimentary Deposits : The soluble products of weathering are carried away in suspension and when such products are deposited, they give rise to the sedimentary deposits.

Chemical Deposits : Some material carried away in solution may be deposited by some phsio – chemical processes such as evaporation , precipitation etc.

Organic Deposits : Some portion of the product of the weathering gets deposited through the agency or organisms.

iii) Metamorphic Rocks :

The rocks formed from the pre- existing rocks with in the earth crust, under the influence of variation in temperature or pressure are called Metamorphic Rocks.

Ex : Marble  , Slate & Gneiss etc.

Formation :

The pre- existing rocks within the earth crust don’t change their state so long as their temperature& pressure remain unchanged known as Metamorphic rocks.

1. Marble : Lime Stone
2. Slate : Shale
3. Quartzite : Sand Stone
4. Gnesis : Granite

Following four types metamorphic occur with various combinations of heat , uniform pressure & directly pressure :

A.) Thermal Metamorphism – The heat is the pre-dominant factor.

B.) Cataclastic Metamorphism – At the surface of earth, the temperature are low & metamorphism is brought about by directed pressure only.

C.) Dynamo – Thermal Metamorphism – There is a rise in temperature with increase in depth. The heat in combination with stress, bring about the changes in rock.

D.) Plutonic Metamorphism : The stress is effective only upto a certain depth. This is due to the fact that rocks become plastic in nature at certain depths. The metamorphic changes at great depths are therefore brought about by uniform pressure & heat.

2) Physical Classification : Based on physical properties.

Further classified into three types :

1. Un-Stratified Rocks :The rocks which don’t show distinct signs of layers and cannot be easily splited up into the layers are called Unstratified rocks. The structure may be crystalline granular ex : Granite, Basalt & traps etc
2. Stratified Rocks : The rocks which show distinct signs of layers and can be easily splited up into layers are called Un-Stratified Rocks. Ex : Sand Stone , Lime Stone etc
3. Foliated Rocks : The rocks which can be splited- up into thin sheets or in a definite direction known as as foliated rocks.

Ex : Slate , Schist etc.

3.) Chemical Classification :

Further classified into three types :

1.) Siliceous Rocks : The rocks having silica (SiCO2) or sand as their major constituent are called Siliceous Rocks.

These rocks are hard & durable. They aren’t easily affected by the weather agencies. Ex: Granite , Sandstone , Quartzite etc.

2.) Argillaceous Rocks : The rocks having Alumina (Al2O3) or clay as their major constituent are known as argillaceous rocks. These rocks may be dense and compact or may be soft like mud stone etc.

3. ) Calcareous Rock : These rocks having calcium carbonate (CaCo3) or lime as their major constituent are called calcareous rocks. The durability of these rocks will depend upon the constituents present in the surrounding atmosphere. Ex : Lime Stone, Marble & Kankar etc.