metamorphic
Rounded quartz-rich cobble, likely quartzite
Quartzite (mostly microcrystalline SiO₂), possibly quartz-rich sandstone or vein quartz
AI-generated identification · may be incorrectHardness about 7 Mohs; pale cream to gray, opaque to slightly translucent, with a dull to sugary vitreous luster and no obvious cleavage. Its rounded, water-worn shape and granular texture suggest a durable quartz-rich rock.
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Physical properties
Hardness about 7 Mohs; pale cream to gray, opaque to slightly translucent, with a dull to sugary vitreous luster and no obvious cleavage. Its rounded, water-worn shape and granular texture suggest a durable quartz-rich rock.
Formation & geological history
Likely formed when quartz sandstone was metamorphosed and recrystallized during mountain-building; quartzite commonly ranges from Precambrian to younger ages. The specimen was later rounded by stream or coastal erosion.
Uses & applications
Used as crushed stone, aggregate, road material, and building/decorative stone; attractive pieces are collected but generally have low commercial value.
Geological facts
Quartzite is notably resistant to weathering and commonly forms ridges, boulders, and resistant stream cobbles. A steel file or knife should leave little or no mark, while quartz-rich grains may scratch glass.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Rocky Mountains, Scandinavia, India, and Australia. Confirm with a hardness test and acid test: it should not fizz in dilute hydrochloric acid unless carbonate cement is present.
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