igneous
Coarse-grained granite (likely biotite granite)
Granite; primarily quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectHardness about 6–7 Mohs; black, white, and gray speckled appearance with a granular texture, vitreous quartz luster, and no obvious foliation. Crystals are interlocking and typically millimeter-scale; feldspar cleavage may be visible.
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Physical properties
Hardness about 6–7 Mohs; black, white, and gray speckled appearance with a granular texture, vitreous quartz luster, and no obvious foliation. Crystals are interlocking and typically millimeter-scale; feldspar cleavage may be visible.
Formation & geological history
Intrusive igneous rock formed by slow cooling of silica-rich magma deep in the crust, generally during Precambrian to Phanerozoic plutonic events. The image is consistent with granite, though exact identification may require a fresh surface or testing.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and building stone; attractive pieces are collected as teaching or display specimens. Small common hand specimens usually have modest value.
Geological facts
Quartz is commonly translucent gray, feldspar is white or pink, and biotite produces the black flakes. Granite differs from basalt by its lighter color and visibly coarse crystals.
Field identification & locations
Identify by its interlocking quartz–feldspar–mica grains, light overall color, and lack of layering; a glassy quartz grain and feldspar cleavage are useful clues. Common worldwide in continental mountain belts and exposed batholiths.
