igneous
Coarse-grained granite
Granite; quartz–alkali feldspar–plagioclase rock with biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7; speckled white/gray, pinkish, and black; generally vitreous quartz and pearly feldspar luster; interlocking phaneritic crystals with no obvious foliation or cleavage. Typical density is 2.6–2.7 g/cm³.
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Physical properties
Hardness about 6–7; speckled white/gray, pinkish, and black; generally vitreous quartz and pearly feldspar luster; interlocking phaneritic crystals with no obvious foliation or cleavage. Typical density is 2.6–2.7 g/cm³.
Formation & geological history
Slow cooling of silica-rich magma deep in the crust produced the visible coarse crystals, commonly during Precambrian to Mesozoic continental plutonism. The specimen may also be granodiorite, which has more plagioclase than true granite.
Uses & applications
Widely used as crushed aggregate, building stone, paving, monuments, countertops, and ornamental slabs. Ordinary hand specimens have little collector value.
Geological facts
The black minerals are likely biotite and/or hornblende; pale crystals are feldspars and translucent grains are quartz. Its granular texture distinguishes it from volcanic rhyolite.
Field identification & locations
Common in exposed crystalline uplands and as transported cobbles; plausible around northeastern Mexico, although local sedimentary rocks are also abundant. Identify with a glass-scratching hardness, quartz grains, and lack of layering; acid testing should show no fizz.
