metamorphic
Iron-stained quartzite or chert
Quartzite, predominantly SiO₂, with iron-oxide staining
AI-generated identification · may be incorrectGray-brown, massive, fine- to medium-grained, with a dull to waxy luster and no obvious cleavage; quartz hardness is about Mohs 7, and specific gravity is roughly 2.6. The rounded, weathered surface suggests natural abrasion or a tumbled specimen.
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Physical properties
Gray-brown, massive, fine- to medium-grained, with a dull to waxy luster and no obvious cleavage; quartz hardness is about Mohs 7, and specific gravity is roughly 2.6. The rounded, weathered surface suggests natural abrasion or a tumbled specimen.
Formation & geological history
Likely formed from quartz-rich sandstone recrystallized during metamorphism, with later oxidation producing brown iron staining; its precise geological age cannot be determined from the photograph. A chert identification is also possible if the texture is uniformly microcrystalline.
Uses & applications
Common quartzite is used as crushed stone, aggregate, paving, and decorative rock; attractive pieces may be collected or used as lapidary material. This specimen does not appear gem-grade.
Geological facts
Quartzite breaks across quartz grains rather than around them and commonly produces a sugary texture; chert typically has a smoother waxy surface and conchoidal fracture.
Field identification & locations
Test with a steel file or glass: true quartz-rich material should resist scratching glass, though surface weathering can affect results. Common sources include metamorphic belts worldwide; a fresh broken surface, acid test, and locality information would improve identification.
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