igneous
Granite
Granite, a coarse-grained felsic intrusive igneous rock composed mainly of quartz, potassium feldspar, and plagioclase, with dark biotite or amphibole
AI-generated identification · may be incorrectPink-tan and gray with conspicuous black mineral grains; interlocking, visible crystals and no cleavage as a rock. Quartz has Mohs hardness 7, feldspars about 6; overall specific gravity is typically 2.6–2.7.
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Physical properties
Pink-tan and gray with conspicuous black mineral grains; interlocking, visible crystals and no cleavage as a rock. Quartz has Mohs hardness 7, feldspars about 6; overall specific gravity is typically 2.6–2.7.
Formation & geological history
Forms when silica-rich magma cools slowly underground, allowing large crystals to grow. Granite occurs in continental crust and ranges widely in age, from Archean rocks over 2.5 billion years old to much younger intrusions.
Uses & applications
Widely used as dimension stone, countertops, paving, monuments, and crushed aggregate; attractive pieces are collected as specimens.
Geological facts
Its speckled appearance comes from contrasting light-colored quartz and feldspar with dark mica or amphibole.
Field identification & locations
Identify it by coarse interlocking crystals and a mix of quartz, feldspar, and dark minerals; it is common in continental mountain belts worldwide. The specimen appears to be a rounded, weathered granite pebble.
