igneous
Biotite-rich granite or granitic gneiss
Quartz–feldspar–biotite granite; possibly foliated granitic gneiss
AI-generated identification · may be incorrectCoarse-grained, mottled cream, gray, and black rock with visible feldspar, quartz, and dark biotite mica. Typical hardness is about 6–7 Mohs; luster is vitreous to pearly, with interlocking crystals and weak or absent cleavage as a whole.
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Physical properties
Coarse-grained, mottled cream, gray, and black rock with visible feldspar, quartz, and dark biotite mica. Typical hardness is about 6–7 Mohs; luster is vitreous to pearly, with interlocking crystals and weak or absent cleavage as a whole.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic tectonic events; gneissic texture develops if later subjected to intense heat and pressure. The image alone cannot establish its exact age or whether it is granite versus gneiss.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and landscaping rock; attractive pieces may be collected but usually have modest value.
Geological facts
The dark flakes are likely biotite, while pale grains are feldspar and translucent gray grains may be quartz. Its coarse texture records slow underground cooling.
Field identification & locations
Identify it by its interlocking visible crystals, hardness, lack of fizz in dilute acid, and inability to scratch with a steel knife easily; common worldwide in continental crust and mountain belts.
