mineral

Tumbled quartz-rich pebble, possibly agate or chalcedony

Microcrystalline quartz (SiO₂), with possible iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; brown to gray, semi-translucent areas, and a dull-to-waxy luster. The rounded shape is tumbled or naturally water-worn; internal structure appears microcrystalline, but banding is not clearly visible.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed when silica-rich groundwater filled cavities or fractures in volcanic rock, later weathered and rounded by transport. The exact geological age and source cannot be determined from the photograph.

Uses & applications

Used as a lapidary material for cabochons, beads, carvings, and decorative stones; comparable agate and chalcedony are also collected as specimens.

Geological facts

The pale, vein-like surface patterns may represent quartz or chalcedony filling fractures, while the darker brown coloration may come from iron oxides. A glass-scratch test can help confirm quartz hardness, though it may damage the specimen.

Field identification & locations

Common in stream gravels and volcanic regions worldwide, including Brazil, Uruguay, Mexico, the western United States, and many European localities. Look for waxy luster, conchoidal fracture, translucency, and hardness; acid reaction should be absent.