(a)List three characteristics of metamorphic rocks. (b)Describe three modes of formation of metamorphic rock (c)Outline three economic benefits of rocks.

Answer Details

(a) Three characteristics of metamorphic rocks

• They are usually hard, compact and crystalline.
• Many show foliation or banding (arrangement of minerals in parallel layers), e.g. gneiss and schist.
• They are generally non-porous and often lack fossils (any fossils present are usually distorted).
• They are formed from pre-existing (parent) rocks that have been changed by heat and/or pressure.

(b) Three modes of formation of metamorphic rock

• Thermal (contact) metamorphism: rocks in contact with hot molten magma are changed by intense heat, e.g. limestone becomes marble.
• Dynamic (regional) metamorphism: great pressure during earth movements (folding and faulting) over large areas changes the rocks, e.g. shale becomes slate then schist.
• Thermo-dynamic metamorphism: combined action of both heat and pressure changes the rock, e.g. granite becomes gneiss.

Common examples: limestone becomes marble; sandstone becomes quartzite; shale/clay becomes slate; coal becomes graphite.

(c) Three economic benefits of rocks

• They supply building and construction materials (marble, granite, limestone for cement, sand and gravel).
• They contain valuable minerals and ores (gold, tin, iron, coal, crude oil) that support mining industries.
• They weather to form fertile soils used for agriculture.
• They store underground water (aquifers) and provide sites for reservoirs and dams.
• Attractive rock scenery attracts tourists; rocks also provide raw materials for industries (e.g. limestone for cement, clay for pottery).