mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO₂)

Hardness: 6.5-7 on Mohs scale; Color: Translucent tan, grey, and dark brown; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.58-2.64.

Hardness: 6
Color: Translucent tan, grey, and dark brown
Luster: Waxy to vitreous

Identified March 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. This specimen likely weathered out of its host matrix into a stream or river bed, resulting in its water-worn, smooth shape.

Uses & applications

Used in jewelry (beads, cabochons), as an abrasive in industrial polishing, for mortar and pestles due to hardness, and widely collected as a semi-precious gemstone.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without extreme magnification. When it shows banding, it is called Agate; when it is opaque and dull, it is called Chert or Jasper.

Field identification & locations

Identify in the field by its waxy texture, translucency when held to light, and ability to scratch glass. Commonly found in riverbeds, gravel pits, and volcanic regions globally (notably Brazil, India, and the Western USA).

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