igneous
Mottled granite (likely weathered granite or granitic gneiss)
Granite; primarily quartz (SiO₂), feldspar, and biotite/amphibole
AI-generated identification · may be incorrectCoarse-grained, pink-gray and black, with a granular texture and dull to slightly vitreous luster. Typical hardness is about 6–7 Mohs; crystals are interlocking, with no prominent cleavage as a whole, though feldspar shows cleavage.
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Physical properties
Coarse-grained, pink-gray and black, with a granular texture and dull to slightly vitreous luster. Typical hardness is about 6–7 Mohs; crystals are interlocking, with no prominent cleavage as a whole, though feldspar shows cleavage.
Formation & geological history
Formed when silica-rich magma slowly cooled deep underground, producing visible crystals; most examples are Precambrian to Phanerozoic in age. The rounded shape and surface texture suggest natural weathering or tumbling.
Uses & applications
Used extensively as dimension stone, countertops, monuments, aggregate, and architectural facing; attractive pieces are collected but are generally low-value.
Geological facts
Pink areas are commonly potassium feldspar, gray translucent grains are quartz, and dark grains are biotite or amphibole. It may be confused with gneiss if minerals show clear banding, or with rhyolite if crystals are too fine to see.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, pink-gray color, dark speckles, and a hard surface that can scratch glass. Common worldwide, especially in large continental batholiths; likely value is $1–$10 for a small ordinary specimen, or $10–$30 if especially attractive or polished.
