gemstone

Tumbled brown chalcedony or agate

Microcrystalline quartz, SiO₂ (likely chalcedony; banding is not visible)

AI-generated identification · may be incorrect

Small, rounded, polished specimen with brown/tan color and vitreous to waxy luster. Quartz hardness is Mohs 7, with no cleavage, cryptocrystalline structure, and specific gravity about 2.60–2.65.

Identified August 20, 2026More gemstone →

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Physical properties

Small, rounded, polished specimen with brown/tan color and vitreous to waxy luster. Quartz hardness is Mohs 7, with no cleavage, cryptocrystalline structure, and specific gravity about 2.60–2.65.

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures in volcanic rock, depositing microscopic quartz fibers; many deposits formed during the Cenozoic, though agate can occur at various ages.

Uses & applications

Used for inexpensive cabochons, beads, ornaments, lapidary pieces, and geological collections. This tiny polished piece has minimal commercial value.

Geological facts

Chalcedony is quartz whose crystals are too small to see unaided; agate is a banded variety of chalcedony. Brown coloration commonly comes from iron oxides or hydroxides.

Field identification & locations

Identify by its glassy/waxy appearance, conchoidal fracture, hardness, and inability to scratch it with a steel knife; a streak test should be white. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.