Coarse-grained intrusive igneous rock, typically consisting of the minerals quartz, feldspar, and biotite mica. It may be pink or grey, depending on the composition of the feldspar. Granites are chiefly used as building materials.
Granite is formed when magma (molten rock) is forced between other rocks in the Earth's crust. It cools and crystallizes deep underground. As it cools slowly large crystals are formed. Granites often form large intrusions in the core of mountain ranges, and they are usually surrounded by zones of metamorphic rock (rock that has been altered by heat or pressure). Granite areas have characteristic moorland scenery. In exposed areas the bedrock may be weathered along joints and cracks to produce a tor, consisting of rounded blocks that appear to have been stacked upon one another.
Britain's largest quarry, Glensanda, near Fort William, Scotland, produces 5 million tonnes of granite a year.
Jointing of the granite occurs when pressure reduces on the sheets underground following the erosion of the rock layers above. The sheet springs up into a gentle dome, and joints and cracks occur. These are opened up or fall away under weathering processes such as chemical weathering and exfoliation.
The Rock Cycle
altered granite close-up
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