igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar granite with biotite and accessory mica/amphibole
AI-generated identification · may be incorrectCoarse, speckled texture with translucent gray quartz, pale feldspar, black biotite, and reflective mica flakes; crystals are interlocking, with vitreous quartz and pearly mica luster. Hardness is approximately 2.5–3 for biotite, 6–7 for feldspar/quartz; specific gravity about 2.6–2.8.
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Physical properties
Coarse, speckled texture with translucent gray quartz, pale feldspar, black biotite, and reflective mica flakes; crystals are interlocking, with vitreous quartz and pearly mica luster. Hardness is approximately 2.5–3 for biotite, 6–7 for feldspar/quartz; specific gravity about 2.6–2.8.
Formation & geological history
Crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic mountain-building events; if foliated, it may be metamorphosed into gneiss.
Uses & applications
Widely used as dimension stone, countertops, flooring, monuments, aggregate, and crushed stone; attractive polished pieces are used decoratively but are generally low-value.
Geological facts
The dark flakes are commonly biotite mica, which splits into thin elastic sheets. Pink, orange, or cream grains are likely potassium feldspar, while glassy gray grains are quartz.
Field identification & locations
Identify it by its coarse interlocking crystals and abundant quartz–feldspar–dark mica mixture; granite is common worldwide, including India, Brazil, Canada, Scandinavia, and the United States. A fresh surface and streak, hardness, and acid tests help distinguish it from mica schist.
