Geological Classification

Based on their beginning of formation stones are classified into 3 main groups-Igneous, sedimentary and metamorphic rocks.

1. Igneous Rocks: These rocks are formed by solidifying and cooling of the rock masses from their molten magmatic condition of the material of the earth. In general igneous rocks are durable and strong. Granite, trap and basalt are the rocks which are belonging to this category; Granites are formed by slow cooling of the lava under thick cover on the top. Therefore they have crystalline surface. Cooling of lava at the top surface of earth results into non-crystalline and glassy texture. Trap and basalt belongs to this category.
2. Sedimentary Rocks: Due to the reason of weathering action of water, wind and frost presented rocks disintegrates. Disintegrated material is carried by water and wind; the water being most powerful medium. Water which is flowing deposits its suspended materials at some points of obstacles to its flow. These deposited layers of materials consolidated under pressure and by heat. Chemical agents also give contribution to the cementing of the deposits. The rocks therefore formed are, fine grained, more uniform and compact in their nature. They represent a bedded or stratified structure generally Sand stones, lime stones, mud stones etc. belong to this class of rock.
3. Metamorphic Rocks: Previously formed igneous and sedimentary rocks undertake changes due to metamorphic action of pressure and internal heat. For instance due to metamorphic action granite becomes trap, greases, and basalt change to schist and laterite, lime stone converts to marble, sand stone becomes quartzite and mud stone becomes slate.