igneous
Tumbled granite or granitic gneiss
Granite, primarily quartz, alkali feldspar, plagioclase, and dark biotite/amphibole
AI-generated identification · may be incorrectCoarse-grained, mottled white, gray, black, and green; vitreous to dull luster; interlocking crystalline texture; Mohs hardness about 6–7; no consistent cleavage as a whole, though feldspar grains cleave.
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Physical properties
Coarse-grained, mottled white, gray, black, and green; vitreous to dull luster; interlocking crystalline texture; Mohs hardness about 6–7; no consistent cleavage as a whole, though feldspar grains cleave.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in Earth’s crust, generally during Precambrian to Phanerozoic mountain-building events; the rounded surface indicates tumbling or natural abrasion.
Uses & applications
Used as aggregate, building and monument stone, countertops, landscaping material, and inexpensive polished decorative specimens.
Geological facts
The dark grains are likely biotite or amphibole, while the white grains are feldspar and quartz; green coloration may reflect chlorite or altered amphibole.
Field identification & locations
Identify by its visibly interlocking grains and mixed light/dark mineral pattern; common worldwide, especially in mountain belts and continental crust. A more precise identification requires a fresh surface or thin section.
