igneous
Granite (likely weathered granite or granitic gneiss)
Granite; mainly quartz (SiO₂), feldspar, and mica
AI-generated identification · may be incorrectHardness about 6–7 Mohs; coarse-grained, gray-white with dark mica and pinkish feldspar, displaying a glassy to dull luster and interlocking crystals. No obvious cleavage as a rock, though feldspar and mica crystals may cleave.
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Physical properties
Hardness about 6–7 Mohs; coarse-grained, gray-white with dark mica and pinkish feldspar, displaying a glassy to dull luster and interlocking crystals. No obvious cleavage as a rock, though feldspar and mica crystals may cleave.
Formation & geological history
Granite forms when silica-rich magma cools slowly deep underground, producing large crystals; typical bodies range from Precambrian to Cenozoic in age. The specimen may show surface weathering or slight metamorphic fabric, making granitic gneiss another possibility.
Uses & applications
Used extensively for countertops, monuments, dimension stone, aggregate, and paving; attractive polished pieces are collected but are generally low-value.
Geological facts
Its visible speckled texture reflects slow cooling, while dark flakes are commonly biotite mica. A white streak or visible quartz grains help distinguish it from many volcanic rocks.
Field identification & locations
Common in continental mountain belts and exposed shields worldwide, including North America, Europe, India, and Australia. Identify it by coarse interlocking grains, abundant light feldspar/quartz, and hardness sufficient to scratch glass.
