Theory question 304
Rocks(a) List three characteristics of metamorphic rocks. (b) Describe three modes of formation of metamorphic rocks. (c) Outline three economic benefits of rocks.
Show the model answer
(a) Formed by alteration of other rocks; hard and compact; crystalline; often banded or foliated; resistant to erosion; contain no fossils (usually); examples: marble, quartzite, slate, gneiss, schist.
(b) Thermal (contact) metamorphism: rocks are changed by great heat from magma intrusions, e.g. limestone to marble, sandstone to quartzite; dynamic (pressure) metamorphism: great pressure from earth movements changes rocks, e.g. shale to slate; regional (thermo-dynamic) metamorphism: heat and pressure together over large areas, e.g. granite to gneiss; also chemical (metasomatism) when hot fluids change composition.
(c) Building and road materials (granite, marble, sandstone); minerals and ores (tin, gold, coal); raw materials for industries (limestone for cement, clay for pottery); soils form from weathered rocks; aquifers store groundwater; tourism (scenery, caves); fuels (coal, oil in sedimentary rocks).
Give a before-and-after rock example for each mode.