sedimentary

Brown Chalcedony (Agate/Jasper blend)

Silicon dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale), Color: Brown to dark tan with opaque regions, Luster: Waxy to vitreous when polished, Crystal structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific gravity: 2.58-2.64

Hardness: 6

Identified May 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous or sedimentary rocks. It is part of the microcrystalline quartz family, often found in volcanic vugs or as stream-rolled pebbles. Geologically, these can range from very recent to hundreds of millions of years old.

Uses & applications

Primarily used for lapidary work, jewelry (beads, cabochons), carvings, and as decorative tumbled stones in landscaping or collection. In ancient times, it was used for cylinder seals and amulets.

Geological facts

The brown color is typically due to the presence of iron oxide (limonite or goethite) inclusions. Microcrystalline quartz is so fine that individual crystals can only be seen under high magnification.

Field identification & locations

Identify by its waxy luster, smoothness, and 'conchoidal' (shell-like) fracture patterns if chipped. It will easily scratch glass but cannot be scratched by a steel knife. Common in gravel beds and along rocky coastlines.

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