igneous
Biotite granite (probable)
Granite; chiefly quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled white, gray, tan, and dark brown; vitreous quartz and pearly mica luster. Mohs hardness about 6–7; lacks strong cleavage as a whole, though feldspar and mica show cleavage; typical specific gravity 2.63–2.75.
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Physical properties
Coarse-grained, speckled white, gray, tan, and dark brown; vitreous quartz and pearly mica luster. Mohs hardness about 6–7; lacks strong cleavage as a whole, though feldspar and mica show cleavage; typical specific gravity 2.63–2.75.
Formation & geological history
A plutonic igneous rock crystallized slowly from silica-rich magma deep in Earth’s crust, producing visible interlocking crystals. Its exact geological age cannot be determined from the photograph; granite commonly ranges from Precambrian to Cenozoic.
Uses & applications
Widely used as dimension stone, countertops, monuments, crushed aggregate, and building material; attractive pieces may be sold as teaching or lapidary specimens.
Geological facts
The dark flakes are likely biotite, while translucent grains are quartz and pale grains are feldspar. A fresh broken surface is more diagnostic than a weathered exterior.
Field identification & locations
Common worldwide, especially in continental mountain belts and ancient shields. Identify it by its coarse interlocking texture, quartz-rich appearance, and lack of layering; acid testing and a hardness test can help distinguish it from limestone or softer rocks.
