igneous
Weathered quartz-rich rock, likely granite or gneiss
Indeterminate granitic rock; mainly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, gray-tan, mottled, and weakly foliated or fractured, with dull to vitreous quartz and feldspar grains. Typical hardness is about 6–7 Mohs; cleavage occurs in feldspar and mica, while quartz has none. Exact identification is limited by the image.
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Physical properties
Coarse-grained, gray-tan, mottled, and weakly foliated or fractured, with dull to vitreous quartz and feldspar grains. Typical hardness is about 6–7 Mohs; cleavage occurs in feldspar and mica, while quartz has none. Exact identification is limited by the image.
Formation & geological history
Likely formed by slow crystallization of silica-rich magma deep underground, possibly followed by metamorphic deformation; commonly Precambrian to Phanerozoic in age. Surface weathering has produced the brown staining and rough texture.
Uses & applications
Used as crushed aggregate, building stone, landscaping material, and occasionally as a decorative slab or specimen. Ordinary pieces have little jewelry value.
Geological facts
The pale grains are consistent with quartz and feldspar, while darker patches may be biotite or hornblende. A fresh broken surface and a hand lens would distinguish granite from banded gneiss.
Field identification & locations
Common in continental crust and exposed in mountain belts, shields, and granitic plutons worldwide. Look for visible interlocking crystals, quartz that scratches glass, and—if present—parallel mineral banding indicating gneiss.
