gemstone

Polished/tumbled brown chalcedony, likely mahogany obsidian or jasper

Chalcedony (microcrystalline quartz, SiO₂) or volcanic glass (obsidian, SiO₂)

AI-generated identification · may be incorrect

The glossy, dark reddish-brown specimen has rounded tumbled edges and pale reflective inclusions. If chalcedony/jasper, hardness is about 6.5–7 Mohs with waxy to vitreous luster; if obsidian, hardness is 5–5.5 and it shows glassy conchoidal fracture.

Identified August 15, 2026More gemstone →

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Physical properties

Formation & geological history

Chalcedony and jasper form from silica-rich groundwater filling cavities or replacing rock; obsidian forms when rhyolitic lava cools too rapidly to crystallize, commonly during the Quaternary and older volcanic episodes.

Uses & applications

Used as inexpensive cabochons, beads, carvings, and decorative stones; jasper and chalcedony are also collectible, while obsidian is used for ornaments and experimental blades.

Geological facts

The image cannot reliably distinguish polished jasper/chalcedony from mahogany obsidian; the bright spots may be quartz, feldspar, or surface reflections.

Field identification & locations

Check translucency at the edges, fracture, and hardness: quartz will scratch glass, whereas obsidian generally will not. Common sources include Brazil, Mexico, the western United States, Madagascar, and Australia.