igneous
Granite (possibly granitic gneiss)
Felsic plutonic rock dominated by quartz, K-feldspar, plagioclase, biotite and/or hornblende
AI-generated identification · may be incorrectCoarse-grained, mottled pink, white, gray and black; vitreous quartz and feldspar with dark mica/amphibole. Typical hardness is about 6–7 Mohs, with no distinct cleavage as a whole and specific gravity around 2.6–2.7.
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Physical properties
Coarse-grained, mottled pink, white, gray and black; vitreous quartz and feldspar with dark mica/amphibole. Typical hardness is about 6–7 Mohs, with no distinct cleavage as a whole and specific gravity around 2.6–2.7.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events; the rounded form indicates transport as a cobble or deliberate polishing.
Uses & applications
Widely used for countertops, building stone, monuments, paving and aggregate; attractive polished pieces are collected but usually have modest value.
Geological facts
The large interlocking crystals indicate intrusive cooling rather than volcanic eruption. Dark minerals may weather preferentially, producing the rough, pitted surface visible here.
Field identification & locations
Identify it by visible interlocking quartz, feldspar and dark minerals, unlike sedimentary rock’s layers or volcanic rock’s fine texture. Common in continental shields, mountain batholiths and stream gravels.
