gemstone

Polished brown agate/chalcedony

Microcrystalline quartz (SiO₂), likely brown chalcedony or agate

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent brown to honey coloration, waxy-to-glassy luster, conchoidal fracture, and no visible cleavage. The curved internal banding and uneven translucent zones are consistent with chalcedony/agate, though the specimen appears polished or tumbled.

Identified September 15, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures, depositing cryptocrystalline quartz in layers; commonly associated with volcanic rocks, especially Cenozoic basalts and ancient lava flows. Exact age and locality cannot be determined from the image.

Uses & applications

Used for cabochons, beads, carvings, polished display stones, and inexpensive jewelry; agate is also used for decorative objects and precision stone surfaces.

Geological facts

Brown color commonly results from iron oxides or hydroxides. Agate is technically banded chalcedony, while relatively uniform material is usually called chalcedony or jasper depending on opacity.

Field identification & locations

Look for translucency, waxy luster, conchoidal edges, hardness sufficient to scratch glass, and curved banding; it should not fizz in dilute acid. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.