gemstone

Polished agate (likely moss/botryoidal agate)

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

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, brown, red, and cream with a waxy-to-glassy luster and cryptocrystalline structure. The rounded, polished form obscures natural banding; iron oxides likely create the red-brown patches.

Identified August 16, 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 quartz in layers or botryoidal growths. Individual pieces may range from Paleozoic to Cenozoic in age, depending on locality.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative objects; small tumbled pieces generally have modest value.

Geological facts

Agate is a variety of chalcedony, and its patterns commonly reflect changing chemistry during repeated silica deposition. The specimen may also be jasper-bearing agate because of its opaque red areas.

Field identification & locations

Identify by its very high polish, quartz-like hardness, translucency, and irregular chalcedony color zoning; it should resist scratching by a steel knife. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.