igneous
Weathered quartz-rich cobble
Probable quartzite or quartz-rich metamorphic rock; exact identification requires a fresh surface and testing
AI-generated identification · may be incorrectHardness approximately 6.5–7 Mohs; gray-brown, granular, dull to slightly glassy luster, massive texture, and no obvious cleavage. The pale translucent grains and strong resistance to weathering suggest abundant quartz, possibly with feldspar or mica.
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Physical properties
Hardness approximately 6.5–7 Mohs; gray-brown, granular, dull to slightly glassy luster, massive texture, and no obvious cleavage. The pale translucent grains and strong resistance to weathering suggest abundant quartz, possibly with feldspar or mica.
Formation & geological history
Likely formed by metamorphism or cementation of quartz-rich sand, then rounded by stream or glacial transport; age cannot be determined from the photograph. Its weathered iron-bearing surface produces the brown coloration.
Uses & applications
Common quartzite is used as aggregate, road stone, landscaping stone, and building material; attractive pieces may be collected or polished, but this specimen appears ordinary.
Geological facts
Quartzite commonly breaks across quartz grains rather than around them and can scratch ordinary glass. The specimen’s rounded shape indicates substantial transport or prolonged abrasion.
Field identification & locations
Look for a sugary fused texture, very high hardness, and lack of reaction to dilute acid; a steel file should barely mark it. Common worldwide, especially in quartz-rich metamorphic terrains and river gravels.
