mineral

Chalcedony (Agate/Carnelian)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Waxy brown, orange-red, white/gray; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None; Fracture: Conchoidal.

Hardness: 6
Color: Waxy brown, orange-red, white/gray
Luster: Waxy to vitreous

Identified June 23, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Waxy brown, orange-red, white/gray; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None; Fracture: Conchoidal.

Formation & geological history

Formed through the deposition of silica-rich groundwater in cavities or veins within volcanic (igneous) or sedimentary rocks. Usually formed in post-volcanic environments.

Uses & applications

Used primarily in lapidary work for jewelry, ornamental carvings, and as a semi-precious gemstone. Also used for industrial abrasive tools due to its hardness.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope. The reddish-brown varieties are known as carnelian.

Field identification & locations

Look for a waxy luster and translucency when held to the light. It is often found as nodules or filling cracks in host rocks. Commonly found in riverbeds or coastal areas where the surrounding softer rock has eroded.