igneous
Granite (likely biotite granite)
Coarse-grained felsic intrusive rock composed mainly of quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectTypically Mohs 6–7; gray to black, granular, with vitreous quartz and pearly/dark mica. Interlocking crystals show no foliation or cleavage as a whole; density is about 2.6–2.8 g/cm³.
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Physical properties
Typically Mohs 6–7; gray to black, granular, with vitreous quartz and pearly/dark mica. Interlocking crystals show no foliation or cleavage as a whole; density is about 2.6–2.8 g/cm³.
Formation & geological history
Formed when silica-rich magma slowly cooled and crystallized deep in Earth’s crust, commonly during Precambrian to Phanerozoic mountain-building events. The rounded shape indicates weathering, transport, or deliberate polishing/tumbling.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and building cladding; attractive pieces are collected but usually have modest value.
Geological facts
The visible speckled texture is called phaneritic and reflects slow cooling. Dark minerals may include biotite, hornblende, or minor magnetite.
Field identification & locations
Identify it by its coarse interlocking quartz-feldspar-mica grains, lack of layering, and inability to scratch with a steel knife; quartz may scratch glass. Common worldwide in continental crust and exposed mountain ranges.
