Rocks

Down to a depth of 16 km from the surface of land, 95 per cent of the earth materials found in the earth’s crust consist of rocks.  Rocks are made up of individual substances, called minerals, found mostly in solid state. Rocks are usually classified into the following three major types.

1. Igneous : These rocks are formed directly from the molten material, when it gets solidified, e.g. Mica, Granite, etc.

2.Sedimentary : These rocks are formed from materials which have accumulated as a result of building up of particles derived from other rocks or from the remains of organically formed matter or from deposits created by chemical action, e.g., Gravel, Peat, Gypsum, etc.

3. Metamorphic : These rocks were originally igneous or sedimentary but have been changed by pressure, heat or action of water, e.g. Gneiss, Marble, Quartzite, etc.