igneous
Coarse-grained granite or granitic gneiss
Granite; primarily quartz (SiO₂), feldspar, and mica, possibly metamorphosed to gneiss
AI-generated identification · may be incorrectHardness about 6–7 Mohs; mottled white, gray, black, and tan with a granular texture and generally vitreous to dull luster. Interlocking quartz and feldspar crystals are visible, though the specimen’s blurred image makes foliation and exact identification uncertain.
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Physical properties
Hardness about 6–7 Mohs; mottled white, gray, black, and tan with a granular texture and generally vitreous to dull luster. Interlocking quartz and feldspar crystals are visible, though the specimen’s blurred image makes foliation and exact identification uncertain.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to younger mountain-building events; gneiss forms when granite is subjected to intense heat and pressure. Common worldwide, including India, Brazil, Scandinavia, Canada, and the United States.
Uses & applications
Widely used as building stone, countertops, monuments, aggregate, and landscaping material; attractive pieces are collected but are generally inexpensive.
Geological facts
Granite’s visible crystals record slow underground cooling, while dark minerals commonly include biotite or hornblende. A glassy quartz grain, hardness, and lack of reaction to dilute acid help distinguish it from limestone.
Field identification & locations
Identify by coarse interlocking crystals, abundant light feldspar/quartz, and scattered dark mica or amphibole; banding would favor gneiss. A fresh, unweathered surface and a hardness or streak test improve accuracy.
