igneous
Tumbled granite or granitic gneiss
Granite, typically quartz + feldspar + mica; possibly foliated granitic gneiss
AI-generated identification · may be incorrectCoarse, speckled gray-white material with black mica/amphibole; vitreous to dull luster, interlocking crystals, no obvious cleavage as a whole. Hardness is approximately 6–7 Mohs; density about 2.6–2.8 g/cm³.
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Physical properties
Coarse, speckled gray-white material with black mica/amphibole; vitreous to dull luster, interlocking crystals, no obvious cleavage as a whole. Hardness is approximately 6–7 Mohs; density about 2.6–2.8 g/cm³.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in continental crust, commonly during Precambrian to younger plutonic events; gneiss forms when granite is intensely metamorphosed. The rounded shapes indicate human tumbling or natural abrasion.
Uses & applications
Used as aggregate, building and monument stone, countertops, landscaping rock, and inexpensive tumbled-stone specimens.
Geological facts
Granite’s visible grains formed because magma cooled slowly underground; its quartz and feldspar content makes it resistant to weathering.
Field identification & locations
Identify it by coarse interlocking grains, pale feldspar/quartz, and dark mica or amphibole; a streak test is usually white, and steel should not readily scratch fresh quartz-rich areas. Common worldwide, especially in continental shields and mountain belts.
