metamorphic

Polished dark pebble, possibly jasper or iron-rich quartzite

Uncertain from the photo; likely iron-stained quartz-rich rock (quartzite) or opaque microcrystalline quartz (jasper)

AI-generated identification · may be incorrect

Small, rounded and polished, with a dark brown-black body and a few lighter reflective areas. Quartz-rich material is typically Mohs 6.5–7, vitreous to waxy, and lacks obvious cleavage; the image does not show enough detail to confirm mineral composition or specific gravity.

Identified October 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Could have formed through metamorphism of quartz sandstone or silica-rich fluid deposition, then been rounded by natural transport or tumbling. The specimen’s age and exact origin cannot be determined visually.

Uses & applications

Likely a decorative or collectible tumbled stone; quartzite is also used as aggregate and building stone, while jasper is used in jewelry and ornaments.

Geological facts

The reported Rondônia, Brazil, area includes diverse crystalline basement and sedimentary terrains, so a quartz-rich pebble is plausible, but the location cannot identify it conclusively.

Field identification & locations

A firm identification would require close inspection or tests: check for a glassy/waxy surface, hardness, streak, and whether it scratches glass. The photo alone cannot distinguish jasper from quartzite or another dark pebble.