metamorphic
Tumbled brown quartzite or chert
Quartzite, predominantly microcrystalline quartz (SiO₂); exact identification is uncertain from an image
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; opaque tan-brown, fine-grained, weathered surface, and dull to subtly waxy luster. It appears massive with no visible cleavage and likely has specific gravity near 2.6–2.7.
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Physical properties
Hardness about 6.5–7 Mohs; opaque tan-brown, fine-grained, weathered surface, and dull to subtly waxy luster. It appears massive with no visible cleavage and likely has specific gravity near 2.6–2.7.
Formation & geological history
Quartzite forms when quartz-rich sandstone is metamorphosed under heat and pressure; chert-like material forms by silica precipitation or replacement. Such rounded pieces may be river-worn or commercially tumbled, and their geological age cannot be determined visually.
Uses & applications
Used as aggregate, paving and decorative stone; attractive polished pieces may be sold as inexpensive lapidary specimens or worry stones.
Geological facts
The white mottling may represent quartz-rich patches, weathering, or minor feldspar/carbonate alteration. A glass-scratch test is useful: genuine quartz-rich material should scratch ordinary glass.
Field identification & locations
Common in quartzite-bearing metamorphic terrains and river gravels worldwide. Confirm with a hardness test, streak (white), absence of acid reaction, and inspection for sandstone layering or conchoidal chert fracture.
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