gemstone

Tumbled brown chalcedony or agate

Microcrystalline quartz (SiO₂), likely chalcedony; possibly iron-stained jasper or agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown to reddish-brown, translucent at thin edges, with a waxy to subvitreous luster. Cryptocrystalline quartz lacks visible crystal faces and has no cleavage; specific gravity is about 2.58–2.65.

Identified August 19, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures in volcanic rock, often with iron-oxide staining and occasional banding. Most specimens are Cenozoic to older, depending on locality; the image alone cannot establish age.

Uses & applications

Used for cabochons, beads, carvings, polished stones, and decorative objects; durable varieties are also used as lapidary material. This appears to be a small tumbled piece rather than a high-value faceted gemstone.

Geological facts

Chalcedony is quartz made of microscopic intergrowths of quartz varieties. Brown coloration commonly results from hematite or goethite inclusions.

Field identification & locations

Identify it by its smooth tumbly form, waxy luster, translucency, and quartz-level hardness; it should resist scratching by a steel knife but scratch glass. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.