igneous
Tumbled granite (likely biotite granite)
Granite: quartz + feldspar + biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled gray-white and black, with vitreous quartz and generally nonmetallic luster; hardness about 6–7 Mohs, no consistent cleavage as a whole, and specific gravity roughly 2.63–2.75. The rounded shape indicates tumbling or natural abrasion.
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Physical properties
Coarse-grained, speckled gray-white and black, with vitreous quartz and generally nonmetallic luster; hardness about 6–7 Mohs, no consistent cleavage as a whole, and specific gravity roughly 2.63–2.75. The rounded shape indicates tumbling or natural abrasion.
Formation & geological history
Intrusive igneous rock formed when silica-rich magma slowly crystallized deep underground, typically during Precambrian to Phanerozoic mountain-building events. The visible crystals are interlocking quartz, feldspar, and dark mica or amphibole.
Uses & applications
Used widely as dimension stone, countertops, monuments, aggregate, landscaping rock, and inexpensive polished collectibles; rarely used as jewelry except in ornamental spheres or cabochons.
Geological facts
Granite’s texture records slow cooling, unlike fine-grained volcanic rocks such as rhyolite. Dark flakes may be biotite mica, while cloudy white areas are likely feldspar or quartz.
Field identification & locations
Identify it by its visibly interlocking crystals, gray-pink-white feldspar, glassy quartz, and black mica; a hand lens and hardness testing help distinguish it from quartzite or manufactured glass. Common worldwide, especially in continental shields and mountain belts.
