igneous
Granite (likely biotite granite)
Granite; primarily quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled gray-and-black rock with pale feldspar and dark mica; typical hardness 6–7 Mohs, glassy to dull luster, interlocking crystals, and no cleavage as a whole. The image is slightly blurred, so exact identification is approximate.
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Physical properties
Coarse-grained, speckled gray-and-black rock with pale feldspar and dark mica; typical hardness 6–7 Mohs, glassy to dull luster, interlocking crystals, and no cleavage as a whole. The image is slightly blurred, so exact identification is approximate.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow. Individual granite bodies range widely in age, commonly from Precambrian to Mesozoic or younger.
Uses & applications
Widely used for countertops, monuments, building stone, paving, and crushed aggregate; attractive pieces may be collected but are generally low value.
Geological facts
Granite’s strength and resistance to weathering come from its interlocking quartz–feldspar framework. Dark patches commonly reflect biotite or hornblende.
Field identification & locations
Identify it by visible interlocking grains, abundant light feldspar/quartz, and scattered black mica; it is common in continental mountain belts worldwide. A streak test is usually white, and acid produces little or no reaction.
