mineral

Chalcedony

Chalcedony (SiO2)

Hardness: 6.5-7 Mohs. Color: translucent yellow-white or milky grey. Luster: waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None. Specific gravity: 2.58-2.64.

Hardness: 6
Color: translucent yellow-white or milky grey
Luster: waxy to vitreous

Identified June 2, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs. Color: translucent yellow-white or milky grey. Luster: waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None. Specific gravity: 2.58-2.64.

Formation & geological history

Forms in hydrothermal environments or through the precipitation of silica-rich water in cavities and cracks of volcanic rocks or sedimentary formations. It is often found as a secondary mineral filling geodes.

Uses & applications

Used extensively in gemstone jewelry (cabochons), ornamental carvings, and historical talismans. Industrially it can be used for mortar and pestles due to its hardness.

Geological facts

Chalcedony is a broad term that includes agate, carnelian, and onyx. In ancient times, it was believed to ward off evil spirits and was used to carm seals and cylinder cylinder rollers.

Field identification & locations

Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and smooth, water-worn texture when found in riverbeds. It is common in the Pacific Northwest of the USA and various volcanic regions globally.