igneous
Weathered granite (likely biotite granite)
Granite; primarily quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled gray, tan, pink, and black rock with a granular texture and irregular fracture; quartz and feldspar have glassy to dull luster. Hardness is about 6–7 Mohs; no prominent cleavage as a whole, though feldspar and mica cleave; specific gravity about 2.6–2.7.
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Physical properties
Coarse-grained, speckled gray, tan, pink, and black rock with a granular texture and irregular fracture; quartz and feldspar have glassy to dull luster. Hardness is about 6–7 Mohs; no prominent cleavage as a whole, though feldspar and mica cleave; specific gravity about 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma deep within continental crust produced interlocking crystals, commonly during Precambrian to Phanerozoic mountain-building events. Surface weathering has rounded and stained the specimen with iron oxides.
Uses & applications
Used extensively as dimension stone, countertops, monuments, aggregate, and building facing; attractive polished pieces are also sold as decorative specimens. This small weathered fragment has little commercial value.
Geological facts
The visible dark flakes are probably biotite or hornblende, while pink areas are potassium feldspar and translucent grains are quartz. Granite is the intrusive equivalent of rhyolite.
Field identification & locations
Identify it by its coarse interlocking grains, mixed light and dark minerals, and lack of layering or vesicles; a streak test is usually white. Common worldwide, especially in exposed continental batholiths and mountain ranges.
