(a) Explain briefly the processes of formation of (i) igneous rocks; (ii) sedimentary rocks; (iii) metamorphic rocks. (b) Give two examples of each of igneo...

Answer Details

(a) Processes of rock formation

(i) Igneous rocks: They are formed from the cooling and solidification of molten rock material (magma or lava). When magma cools slowly below the earth's surface it forms coarse-grained (intrusive/plutonic) rocks, and when lava cools quickly at the surface it forms fine-grained (extrusive/volcanic) rocks.

(ii) Sedimentary rocks: They are formed when rock fragments and organic remains (sediments) produced by weathering and erosion are transported, deposited in layers and then compacted and cemented together over a long time.

(iii) Metamorphic rocks: They are formed when existing igneous or sedimentary rocks are changed in form/structure by great heat and/or pressure within the earth, without melting completely.

(b) Examples

Igneous (two): granite, basalt (also gabbro).

Metamorphic (two): marble, slate (also gneiss, schist).

Sedimentary (three): limestone, sandstone, shale (also clay).