igneous
Polished pink-and-black granite or gneiss
Granite–gneiss, chiefly quartz, feldspar, and biotite/amphibole
AI-generated identification · may be incorrectMedium- to coarse-grained, pink, gray, white, and black; vitreous to dull luster and interlocking crystals. Hardness about 6–7 Mohs; quartz has no cleavage, feldspar has two cleavages, and specific gravity is approximately 2.6–2.8.
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Physical properties
Medium- to coarse-grained, pink, gray, white, and black; vitreous to dull luster and interlocking crystals. Hardness about 6–7 Mohs; quartz has no cleavage, feldspar has two cleavages, and specific gravity is approximately 2.6–2.8.
Formation & geological history
Likely crystallized as felsic magma deep underground, then was uplifted and weathered into a rounded cobble; if the dark minerals form aligned bands, it may be metamorphic gneiss. Such rocks commonly formed in Precambrian to younger continental crust.
Uses & applications
Used as dimension stone, countertops, architectural aggregate, landscaping stone, and polished decorative specimens; this small cobble has modest collector value.
Geological facts
The pink color generally comes from potassium feldspar, white areas from plagioclase or quartz, and black patches from biotite or amphibole. Strong mineral banding favors gneiss, while a random “salt-and-pepper” texture favors granite.
Field identification & locations
Identify it by its visible interlocking pink feldspar, gray/clear quartz, and black mafic minerals; it is nonvesicular and does not split into thin sheets. Common worldwide, especially in granitic and metamorphic terrains.
