igneous
Rounded granite or granitic gneiss cobble
Granite; primarily quartz, feldspar, and mica (exact identification requires a fresh surface and testing)
AI-generated identification · may be incorrectCoarse-grained, pale gray-beige rock with visible quartz and feldspar, minor dark mica, and rusty iron-oxide staining; typically Mohs hardness 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock. Its rounded shape indicates abrasion by water or glacial transport.
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Physical properties
Coarse-grained, pale gray-beige rock with visible quartz and feldspar, minor dark mica, and rusty iron-oxide staining; typically Mohs hardness 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock. Its rounded shape indicates abrasion by water or glacial transport.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to younger mountain-building events; later exposed and rounded in a river, beach, or glacial deposit.
Uses & applications
Used as dimension stone, architectural aggregate, landscaping rock, riprap, and decorative or polished stone; this ordinary cobble has little jewelry value.
Geological facts
Granite can be distinguished from sandstone by its interlocking crystalline texture rather than obvious sedimentary grains or layers. Rust-colored patches are weathered iron-bearing minerals, not necessarily gold.
Field identification & locations
Common worldwide, especially in continental shields and granitic mountain belts; look for quartz’s glassy grains, white/pink feldspar, and scattered black mica. A hand lens, streak test, and fresh broken surface improve identification.
