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

Answer Details

(a) Three characteristics of metamorphic rocks

• They are hard, compact and crystalline.
• They often show foliation or banding (layers of minerals).
• They contain no fossils (any original fossils are destroyed by heat and pressure) and are usually resistant to erosion.

(b) Three modes of formation of metamorphic rocks

• Thermal (contact) metamorphism: rocks are altered by intense heat when they come into contact with rising hot magma, e.g. limestone changing to marble near an intrusion.
• Dynamic (pressure) metamorphism: rocks are altered by great pressure, especially during earth movements and faulting, which crushes and recrystallises them.
• Regional (dynamo-thermal) metamorphism: rocks over a wide area are changed by the combined action of heat and pressure during mountain-building, e.g. shale to slate to schist to gneiss.

(c) Three economic benefits of rocks

• They provide building and construction materials such as granite, marble, sand and gravel.
• They are a source of valuable minerals and ores (gold, tin, iron, limestone for cement) that support industry and earn revenue.
• They weather to form soils that support agriculture, and some (marble, precious stones) are used for decoration and export.