igneous
Coarse-grained granite or granitic gneiss
Granite; chiefly quartz (SiO₂), feldspar, and dark mica/amphibole. Strong foliation could indicate granitic gneiss.
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray, white, pink, and black grains with a coarse crystalline texture and vitreous to dull luster. Quartz has no cleavage, feldspar shows two cleavages, and specific gravity is typically 2.63–2.75.
Identified More igneous →
Explore Coarse-grained granite or granitic gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 6–7 Mohs; gray, white, pink, and black grains with a coarse crystalline texture and vitreous to dull luster. Quartz has no cleavage, feldspar shows two cleavages, and specific gravity is typically 2.63–2.75.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic continental mountain-building; gneiss forms when granite is intensely metamorphosed. The pictured specimen appears weathered and possibly fractured.
Uses & applications
Widely used as building stone, countertops, monuments, aggregate, and decorative rock; ordinary hand specimens have little commercial value.
Geological facts
Its visible interlocking crystals indicate slow cooling rather than volcanic eruption. Dark bands or streaks may reflect biotite, hornblende, or metamorphic segregation.
Field identification & locations
Identify it by coarse interlocking quartz and feldspar grains, abundant light minerals, and black mica/amphibole; a strong light–dark banding favors gneiss. Common worldwide, especially in continental shields and mountain belts.
