gemstone

Polished agate (likely Botswana or plume agate)

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

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent gray, cream, reddish-brown and bluish areas; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage. The rounded, polished surface and internal banding/inclusions are characteristic of agate.

Identified August 28, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony in successive layers; iron and other impurities create the colors. Most examples formed during volcanic activity in the Cenozoic or older geological periods.

Uses & applications

Used for cabochons, carvings, beads, ornaments, and lapidary slices; also collected as a decorative gemstone. Common polished pieces typically have modest value.

Geological facts

Agate is a variety of chalcedony rather than a separate mineral species. Colorful internal patterns become clearer when wet or viewed with transmitted light.

Field identification & locations

Identify it by its translucency, curved or plume-like internal patterns, waxy luster, and hardness sufficient to scratch glass; it commonly occurs in volcanic regions worldwide, including Brazil, Uruguay, Botswana, Mexico, and the United States.