mineral

Chalcedony

Chalcedony (SiO2)

Hardness: 6.5-7 (Mohs); Color: translucent white to light gray; Luster: waxy to dull; Crystal structure: trigonal (cryptocrystalline); Cleavage: none; Specific gravity: 2.58-2.64

Hardness: 6
Color: translucent white to light gray
Luster: waxy to dull

Identified June 15, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: translucent white to light gray; Luster: waxy to dull; Crystal structure: trigonal (cryptocrystalline); Cleavage: none; Specific gravity: 2.58-2.64

Formation & geological history

Formed by the deposition of silica from water in cavities or veins within rocks, often igneous or sedimentary. It is common in volcanic environments.

Uses & applications

Used for jewelry (cabochons), seals, small carvings, and as a collector's specimen. Historically used for making tools like scrapers.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without a microscope. Agate and Jasper are both varieties of chalcedony.

Field identification & locations

Identify by its waxy luster, conchoidal fracture (curved breaks), and hardness (cannot be scratched by a knife). Frequently found in gravel beds or near volcanic outcrops.