Stone|Formation|Classification|Uses in engineering

Stone

• Stone is a naturally available building material' obtained from Quarry which has been used from the early age of civilization. Stones used for construction of structures are known as building stones. The study of rock, its properties and origin is called Petrology. It is available in the form of rocks, which is cut to required size and shape and used as a building block.

Formation of Stone

Stones are formed in the form of igneous, sedimentary and metamorphic either on the surface of earth or below the surface of the earth. 

Classification of Stone

The rocks may be classified on the basis of their geological formation, physical characteristics and

chemical composition.

Based on Geological Formation

Based on their origin of formation stones are classified into three main groups: Igneous, sedimentary and metamorphic rocks.

1. Igneous Rocks

These rocks are formed by cooling and solidifying of the molten magma on the surface of the earth

or below the surface of the earth. Generally igneous rocks are strong and durable. Its main constituent is silica. For example; Basalt, trap, granite, pegmatite, pumice, gabbro, obsidian, syenite,

dolerite, diorite, etc. During formation of igneous rocks:

--->If magma cools below the surface of the earth, it is called intrusive igneous rock, These rock cools slowly so it has crystalline texture where

--->lf magma cools at shallow depth, called hypabyssal rock. For example; diorite

--->If magma cools at large depth, it is called plutonic rock. For example; Granite and pegmatite

2.Sedimentary Rocks

Due to the weathering action of water, wind and frost existing rocks disintegrate. The disintegrated material is carried by wind and water; the water being the most powerful medium. Flowing water deposits its suspended materials at some points of obstacles to its flow. These deposited layers of materials get consolidated under pressure and by heat. Chemical agents also contribute to the cementing of the deposits. The rocks thus formed are called sedimentary rock, which are more

, fine grained and compact in their nature. They represent a bedded or stratified structure in general. 

For example; Limestone, sandstone, dolomite, diatomite, Gypsum, conglomerate, magnesite,

chalk, gravel, shale, kankar, Tripoli, chert, etc.

3. Metamorphic Rocks

Previously formed igneous and sedimentary rocks undergo changes due to metamorphic action of

pressure and internal heat. The rock thus formed is called metamorphic rock. For example due to

Metamorphic action granite becomes gneisses, trap and basalt change to schist and laterite, limestone changes to marble, sandstone becomes quartzite and mudstone becomes slate. For example

Gneiss, Quartzite, Marble, slate, schist, serpentine, etc.

Based on Physical Characteristics

Based on the physical structure, the rocks may be classified as:

1.Stratified Rocks

These rocks have a layered structure. They possess planes of stratification or cleavage and can be easily split along these planes, slate, etc. Sedimentary rocks like Sandstone, lime stones, marble and

quartzite are the examples of this class of stones.

2. Unstratified Rocks

These rocks are not stratified. They possess crystalline and compact grains. They cannot be split into thin slabs. Igneous rocks like Granite, trap, etc. are the examples of this type of rocks.

3. Foliated Rocks

These rocks have a tendency to split along a definite direction only. The directions need not be parallel to each other as in case of stratified rocks. This type of structure is very common in case of

metamorphic rocks. Metamorphic rocks except marble and quartz are examples of foliated rock.

Based on Chemical Characteristics

On the basis of their chemical composition engineers prefer to classify rocks as:

1. Siliceous rocks

The main content of these rocks is silica. They are hard and durable. Examples of such rocks are granite, trap, basalt, quartzite, gneiss, syenite, sand stones, etc

2. Argillaceous rocks

The main constituent of these rocks is  clay. These stones are hard and durable but they are brittle. They cannot withstand shock. Slates, kaolin and laterites are examples of this type of rock.

3. Calcareous rocks

The main constituent of these rocks is calcium carbonate. Limestone, marble, dolomite, etc. are examples of this type of rocks.