igneous
Polished black-and-white granite
Granite, composed mainly of quartz, feldspar, and dark biotite/amphibole minerals
AI-generated identification · may be incorrectHardness about 6–7 Mohs; coarse crystalline texture with black, gray, and white mottling; vitreous quartz and feldspar luster, generally no cleavage as a whole rock, and specific gravity about 2.63–2.75. The glossy surface indicates cutting and polishing.
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Physical properties
Hardness about 6–7 Mohs; coarse crystalline texture with black, gray, and white mottling; vitreous quartz and feldspar luster, generally no cleavage as a whole rock, and specific gravity about 2.63–2.75. The glossy surface indicates cutting and polishing.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep underground, allowing visible crystals to grow; commonly Precambrian to Phanerozoic in age. The image likely shows a polished architectural slab.
Uses & applications
Widely used for countertops, flooring, monuments, stairs, and building cladding; polished pieces are also sold as decorative specimens. Commercial value varies mainly with rarity, pattern, thickness, and fabrication.
Geological facts
The dark minerals are typically biotite mica and/or amphibole, while pale areas are feldspar and quartz. Flow-like banding may indicate a granitic gneiss or migmatite rather than ordinary granite.
Field identification & locations
Identify it by interlocking visible crystals, strong resistance to scratching, and mottled black-white coloration; unlike marble, it does not fizz readily with dilute acid. Common sources include Brazil, India, China, Scandinavia, and North America.
