igneous
Weathered granite or granitic gneiss
Granite; predominantly quartz (SiO₂), feldspar, and mica/amphibole
AI-generated identification · may be incorrectCoarse-grained, light gray to tan rock with white feldspar/quartz and dark mafic minerals; crystals are interlocking, with a vitreous quartz luster and no obvious cleavage. Typical Mohs hardness is 6–7 and specific gravity about 2.6–2.8.
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Physical properties
Coarse-grained, light gray to tan rock with white feldspar/quartz and dark mafic minerals; crystals are interlocking, with a vitreous quartz luster and no obvious cleavage. Typical Mohs hardness is 6–7 and specific gravity about 2.6–2.8.
Formation & geological history
Formed when silica-rich magma cooled slowly deep in the crust, allowing large crystals to grow; its exact age cannot be determined from the image and may range from Precambrian to younger depending on locality. Surface weathering has rounded and stained the specimen.
Uses & applications
Used as dimension stone, countertops, monuments, aggregate, and crushed-rock construction material; attractive pieces may be collected but are generally not gemstone grade.
Geological facts
Quartz appears gray or glassy, feldspar is typically white/cream, and dark grains are commonly biotite or hornblende. The mottled appearance is characteristic of granitic rocks, though the image cannot reliably distinguish granite from foliated granitic gneiss.
Field identification & locations
Common in continental mountain belts and exposed basement terrains worldwide; identify with a hand lens by its visible interlocking quartz, feldspar, and dark mineral grains. A streak test is usually unhelpful; avoid calling it marble or concrete without locality and testing.
