igneous
Biotite granite
Granite; quartz–alkali feldspar–plagioclase rock with biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled tan, white, gray, and black appearance; interlocking quartz and feldspar crystals with black biotite. Hardness about 6–7; vitreous quartz, feldspathic luster, poor/no cleavage as a rock, specific gravity roughly 2.6–2.7.
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Physical properties
Coarse-grained, speckled tan, white, gray, and black appearance; interlocking quartz and feldspar crystals with black biotite. Hardness about 6–7; vitreous quartz, feldspathic luster, poor/no cleavage as a rock, specific gravity roughly 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma deep in the crust, producing visible crystals; commonly Paleozoic to Precambrian, though granite forms throughout geologic time.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and building material; this small rounded specimen has modest educational or collecting value.
Geological facts
The dark flakes are likely biotite, while translucent gray grains are quartz and cream-colored grains are feldspar. Weathering rounds granite into resistant cobbles and boulders.
Field identification & locations
Identify it by coarse interlocking crystals, abundant light quartz/feldspar, and black mica; it is common in continental mountain belts and glacial deposits worldwide. A streak test is generally unhelpful; a hand lens is useful.
