TOP 10 PSU IN INDIA

STONE-

      Stone is a ‘natural available building material’ which has been used from the early age of civilization. It is available in the form of rocks, which is cut to required size and shape and used as building block. It has been used to convert small residential building to large places and temples all over the world.

Type of Stones

Stone used for civil engineering work may be classified in the following three ways:

·        Geological

·        Physical

·        Chemical

Geological Classification-

Based on their origin of formation stones are classified into three main groups-                              

 (a)     Igneous Rocks

       (b)   Sedimentary Rocks

       (c)    Metamorphic Rocks

   (a)   Igneous Rocks-

These rocks are formed by cooling and solidifying of the rock masses from their molten magmatic condition of the material of the earth. Generally igneous rocks are strong and durable. Granite, trap and basalt are the rocks belonging to the category, Granites are formed by slow cooling of the lava under thick cover on the top. Hence they have crystalline surface. The cooling of lava at the top surface of earth results into non-crystalline and glassy texture. Trap and blast belong to this category.

(b)   Sedimentary Rocks-

Due to this weathering action of water, wind and frost existing rocks disintegrates. The disintegrate material is carried by wind and water being most powerful medium. Flowing water deposit 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 more uniform, fine grained and compact in their nature . They represent a bedded or stratified structure in general . Sand stones, lime stones, mud stones etc. belong to this class of rock.

(c)    Metamorphic Rocks-

Previously formed igneous and sedimentary rocks under go changes due to metamorphic action of pressure and internal heat. For example due to metamorphic action granite becomes greisses, trap and blast change to schist and laterite , lime stone change to marble, sand stone becomes quartzite and mud stone become slate.

Physical Classification-

Based on structure, the rocks may be classified as:

·        Stratified rocks

·        Unstratified rocks

·        Foliated rocks

(i) Stratified Rocks-

These rocks are having layered structure. They possess plane of stratification or cleavage. They can be easily split along these planes. Sand stone, lime stone, slate etc .

Are the examples of this class of stones.

(ii) Unstratified Rocks-

These rocks are not stratified. They posses crystalline and compact grains. They cannot be split in to thin slab. Granite, Trap, Marble etc. are the examples of this type of rocks.

(iii) Foliated Rocks-

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

Chemical Classification-

On the bases of their chemical composition engineers prefers to classify rocks as:

·        Silicious rocks

·        Argillaceous rocks

·        Calcareous rocks

(i)  Silicious rocks-

The main content of these rocks is silica. They are hand and durable. Example of such rocks are granite, trap, sand stone etc.

(ii)   Argillaceous rocks-

The main constituent of these rocks is argil clay. These stone are hard and durable but they are brittle. They can not withstand shock. Slate and laterites are examples of this type of rocks.

(iii) Calcareous rocks-

The main constituent of these rocks is calcium carbonate. Lime stone is a calcareous rocks of sedimentary origin while marble is a calcareous rock of metamorphic origin.