mineral

Chalcedony (Milky Agate/Quartz)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Translucent milky white to pale blue. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (hexagonal). Cleavage: None. Specific gravity: 2.58-2.64.

Hardness: 6
Color: Translucent milky white to pale blue
Luster: Waxy to vitreous

Identified June 24, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Translucent milky white to pale blue. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (hexagonal). Cleavage: None. Specific gravity: 2.58-2.64.

Formation & geological history

Formed from aqueous solutions at relatively low temperatures, typically occurring as a precipitate within the cavities of igneous rocks such as basalt, or as a replacement mineral in sedimentary environments.

Uses & applications

Used primarily in jewelry as cabochons or beads, for ornamental carvings, and historically for making hard-wearing tools or seals.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. It has been used by humans for over 8,000 years, with ancient civilizations like the Minoans using it for cylinder seals.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Commonly found in Brazil, India, Madagascar, and the USA (California and Oregon).

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