gemstone

Polished brown agate/chalcedony pebble

Microcrystalline quartz (SiO₂), likely banded agate or jaspery chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown, cream, and reddish mottling with a waxy-to-glassy luster. Microcrystalline quartz has no visible crystal faces and lacks cleavage; specific gravity is about 2.6.

Identified August 19, 2026More gemstone →

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Physical properties

Hardness 6.5–7 Mohs; brown, cream, and reddish mottling with a waxy-to-glassy luster. Microcrystalline quartz has no visible crystal faces and lacks cleavage; specific gravity is about 2.6.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and iron oxides in successive layers. Agate formation is generally associated with volcanic rocks ranging from Paleozoic to Cenozoic age.

Uses & applications

Used for tumbled stones, cabochons, beads, carvings, ornaments, and small decorative objects; industrial agate is also used for durable grinding surfaces.

Geological facts

The brown coloration commonly comes from iron oxides or hydroxides. Polishing enhances its translucency and reveals subtle internal banding or flow patterns.

Field identification & locations

Identify it by its very smooth polish, quartz-like hardness, waxy appearance, and possible translucency at the edges; glass will usually show bubbles and scratch more easily. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.