igneous
Granite Cobble / River Pebble
Granite (felsic intrusive igneous rock)
AI-generated identification · may be incorrectHardness: 6-7 on Mohs scale; Color: mottled pinkish-brown, tan, gray, and dark green/black; Luster: vitreous to dull due to surface weathering; Texture: medium to coarse-grained (phaneritic) intrusive crystalline texture smoothed by fluvial or glacial abrasion; Specific Gravity: approximately 2.65-2.75
- Hardness
- 6-7 on Mohs scale
- Color
- mottled pinkish-brown, tan, gray, and dark green/black
- Luster
- vitreous to dull due to surface weathering
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Physical properties
Hardness: 6-7 on Mohs scale; Color: mottled pinkish-brown, tan, gray, and dark green/black; Luster: vitreous to dull due to surface weathering; Texture: medium to coarse-grained (phaneritic) intrusive crystalline texture smoothed by fluvial or glacial abrasion; Specific Gravity: approximately 2.65-2.75
Formation & geological history
Formed through the slow crystallization of silica-rich (felsic) magma deep beneath the Earth's crust (plutonic environment). Subsequently exposed via uplift and erosion, then rounded naturally by water tumbling in a riverbed or coastal environment, or transport by glacial action.
Uses & applications
Commonly used in landscaping, river rock decor, crushed aggregate for construction, and decorative garden borders. In unweathered slab form, granite is widely quarried for countertops, monuments, and building facing.
Geological facts
Granite makes up a major portion of the Earth's continental crust. Over millions of years, rough fractured blocks of granite tumble down rivers and along shorelines, gradually rounding into spherical or oval cobblestones due to hydraulic abrasion.
Field identification & locations
Identified by interlocking grains of pink-to-tan alkali feldspar/plagioclase, translucent quartz, and dark specks of biotite mica or amphibole, combined with a naturally water-rounded, smooth exterior. Widely found in gravel pits, riverbanks, and glacial drift worldwide.
