metamorphic
Rounded quartz-rich cobble, likely quartzite or silicified sandstone
Quartzite (mostly microcrystalline SiO₂), possibly quartz-cemented sandstone
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; pale cream to tan, dull-to-vitreous luster, massive texture, and no obvious cleavage. The rounded shape and weathered surface indicate prolonged abrasion, likely in a stream or gravel deposit.
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Physical properties
Hardness about 6.5–7 Mohs; pale cream to tan, dull-to-vitreous luster, massive texture, and no obvious cleavage. The rounded shape and weathered surface indicate prolonged abrasion, likely in a stream or gravel deposit.
Formation & geological history
If quartzite, it formed when quartz-rich sandstone was compacted and recrystallized during metamorphism; if sandstone, it formed from lithified sand and silica cement. Its precise geological age and origin cannot be determined from the photograph alone.
Uses & applications
Commonly used as durable aggregate, road stone, landscaping material, and occasionally decorative stone; attractive quartzite may be polished or used in countertops.
Geological facts
Quartzite commonly breaks across quartz grains rather than around them, producing a hard, irregular fracture. The specimen appears natural and unpolished, though surface staining and weathering obscure its texture.
Field identification & locations
Look for quartz grains, a sugary recrystallized texture, and inability to scratch it with a steel knife; quartzite typically scratches glass. Common in metamorphic belts and river gravels worldwide; acid testing is usually unhelpful.
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