igneous
Granite (likely biotite granite or granodiorite)
Coarse-grained intrusive felsic rock composed mainly of quartz, K-feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled white, gray, tan, and black with granular texture, vitreous quartz, and feldspar cleavage. Crystals are interlocking and phaneritic; specific gravity typically 2.63–2.75.
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Physical properties
Hardness about 6–7 Mohs; mottled white, gray, tan, and black with granular texture, vitreous quartz, and feldspar cleavage. Crystals are interlocking and phaneritic; specific gravity typically 2.63–2.75.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, and aggregate; attractive hand specimens are collected but usually have modest value.
Geological facts
The visible dark grains are likely biotite or hornblende, while translucent gray grains are quartz. Weathering can produce the rusty brown surface staining seen here.
Field identification & locations
Identify it by its coarse interlocking crystals, abundant light minerals, and scattered black mafic grains; common worldwide in continental plutons and exposed mountain belts.
