Mention the economic significance of sedimentary and igneous rocks.

(i) Coal and petroleum are major sources of power.

(ii) Bricks from clay, cement from limestone and glass from sand is obtained.

(iii) Limestone is used for buildings purpose.

The igneous rocks are crystalline rocks and hence are very rich in minerals of great economic value. These minerals are : magralite (iron), nickel, copper, lead, zink, chromite, manganese, gold, diamond, platinum etc. These are of great value in metallurgical industry. Ores of lead, tin, copper are also found mixed with quartz and calcite. Igneous rocks abound in silicate minerals containing iron and magnesium. Some mica are also associated with igneous rocks.

Economic significance of igneous rocks :

(i) Granite is used for house-building and idol-making.

(ii) Pumice stone is used as a sharpener.

(iii) Basalt and dolerite are used for road-making.

(iv) Many minerals found in these rocks e.g iron ore, manganese are basic raw materials for many industries.