igneous
Weathered red granite or granitic gneiss cobble
Granite, chiefly quartz, feldspar, and mica; possibly foliated granitic gneiss
AI-generated identification · may be incorrectPink-red, coarse crystalline texture with dark mica/amphibole flecks; vitreous quartz and feldspar luster, generally Mohs 6–7, massive to weakly banded, with no obvious cleavage as a whole rock.
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Physical properties
Pink-red, coarse crystalline texture with dark mica/amphibole flecks; vitreous quartz and feldspar luster, generally Mohs 6–7, massive to weakly banded, with no obvious cleavage as a whole rock.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust; gneiss forms when granite is metamorphosed under high heat and pressure. Such rocks are commonly Precambrian to younger and may be glacially transported cobbles.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and landscaping rock; this weathered specimen has little commercial or jewelry value.
Geological facts
The red color commonly comes from iron-oxidized potassium feldspar, while black grains are usually biotite or hornblende. Surface weathering can obscure the original crystal boundaries.
Field identification & locations
Common in continental shields and glacial deposits, especially northern North America, Scandinavia, and other crystalline terrains. Look for visible interlocking quartz, pink feldspar, and dark minerals; a fresh broken surface is diagnostic.
