metamorphic
Weathered quartz-rich cobble (probable quartzite or silicified rock)
Quartzite, predominantly SiO₂; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectTan to cream, massive and strongly weathered, with brown iron-oxide staining and dark surface fractures. Quartzite has Mohs hardness about 7, vitreous to dull luster, interlocking quartz grains, no cleavage, and specific gravity around 2.6;…
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Physical properties
Tan to cream, massive and strongly weathered, with brown iron-oxide staining and dark surface fractures. Quartzite has Mohs hardness about 7, vitreous to dull luster, interlocking quartz grains, no cleavage, and specific gravity around 2.6; the specimen’s soft-looking surface may reflect weathering or a different silicified sediment.
Formation & geological history
Likely formed by metamorphism or silica replacement of quartz-rich sandstone, then rounded and weathered in a tropical environment. The regional age cannot be determined from the image; around 17.2°N, 89.1°W, weathered sedimentary rocks and chert/quartzite clasts are plausible.
Uses & applications
Useful as durable aggregate, road stone, building stone, and occasionally as a lapidary material. This ordinary cobble has little commercial or collector value.
Geological facts
Brown branching marks are probably iron-oxide-filled fractures or weathering patterns, not necessarily fossils. A steel file should barely scratch fresh quartzite, while glass is commonly scratched by it.
Field identification & locations
Field-test a fresh edge: quartz-rich material should scratch glass and resist a knife; dilute acid should not fizz. If it is easily scratched or has a waxy conchoidal fracture, chert or silicified limestone is a better regional alternative. Common value: $1–$10 as a specimen, occasionally $10–$30 if polished or unusually patterned.
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