igneous
Granite (likely biotite granite)
Coarse-grained granitic rock; chiefly quartz, potassium feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray to pinkish-gray with black mica/amphibole and pale feldspar, displaying a granular texture and mostly vitreous to pearly luster. Crystals are interlocking and lack cleavage as a whole, though feldspar and mica have cleavage.
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Physical properties
Hardness about 6–7 Mohs; gray to pinkish-gray with black mica/amphibole and pale feldspar, displaying a granular texture and mostly vitreous to pearly luster. Crystals are interlocking and lack cleavage as a whole, though feldspar and mica have cleavage.
Formation & geological history
Slow crystallization of silica-rich magma deep in the continental crust, commonly during Precambrian to Phanerozoic plutonic events; the rounded surface indicates weathering or water transport.
Uses & applications
Widely used as dimension stone, countertops, monuments, building aggregate, and paving; attractive polished pieces are collected but are generally low value.
Geological facts
The gold-brown reflective flakes are likely weathered biotite or iron-stained feldspar, while black grains may be biotite or hornblende. A glassy quartz grain and scratch resistance help distinguish granite from softer sedimentary rocks.
Field identification & locations
Common worldwide, especially in continental shields and mountain batholiths. Identify it by visible interlocking quartz and feldspar crystals, black mafic minerals, and lack of layering or fossils; exact classification requires a thin section or chemical analysis.
