sedimentary/metamorphic

Rounded quartz-rich cobble, likely sandstone or quartzite

Quartz-dominated siliciclastic rock; possibly quartz arenite (sandstone) or quartzite, mainly SiO₂

AI-generated identification · may be incorrect

Brown, tan, gray, and rusty surface with granular texture and rounded stream-worn shape; quartz has Mohs hardness 7, vitreous to dull luster, and no cleavage. The porous, visibly sandy texture favors sandstone; an exceptionally hard, fused texture would indicate quartzite.

Identified September 9, 2026More sedimentary/metamorphic →

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At a glance

Common name: Rounded quartz-rich cobble, likely sandstone or quartzite
Scientific name: Quartz-dominated siliciclastic rock; possibly quartz arenite (sandstone) or quartzite, mainly SiO₂
Category: sedimentary/metamorphic
Identified: September 9, 2026
Method: Standard

AI Estimated Value

About $2–$15 as a common cobble; $15–$50 if unusually attractive, polished, or locality-documented.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Likely formed from quartz sand cemented into sandstone, then rounded by prolonged transport in a river or beach; if metamorphosed, recrystallization produced quartzite. Precise age and origin cannot be determined from the photograph.

Uses & applications

Common varieties are used as aggregate, paving and building stone; attractive polished pieces are sold as décor or teaching specimens, but this example has little gem value.

Geological facts

Rusty coloring commonly comes from iron-oxide staining, while dark patches may be iron minerals or other inclusions. Rounded edges indicate abrasion during transport.

Field identification & locations

Test a fresh surface: abundant visible sand grains and scratching by steel suggest sandstone; a hard, interlocking quartz mosaic that scratches glass suggests quartzite. Common worldwide in sedimentary basins, rivers, and beaches.