gemstone

Tumbled brown agate (likely moss or plume agate)

Microcrystalline quartz, chiefly chalcedony (SiO₂), with iron-oxide and possibly mineral inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent to opaque brown, honey, and olive tones; waxy to vitreous luster; cryptocrystalline structure with no visible cleavage; specific gravity about 2.6. The rounded, glossy surface indicates tumbling and polishing.

Identified August 30, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and inclusions in successive layers. It commonly formed in volcanic terrains from the Paleozoic to Cenozoic eras, though this specimen’s exact age is indeterminate.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and ornamental objects; attractive pieces are collected as lapidary gemstones.

Geological facts

Brown coloration typically comes from iron oxides or hydroxides. Internal mossy or plume-like patterns may be caused by dendritic iron or manganese minerals rather than organic material.

Field identification & locations

Identify by its very fine quartz texture, waxy luster, translucency at thin edges, and exceptional scratch resistance; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, India, Mexico, and the western United States.