mineral

Chalcedony

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grayish-blue, translucent; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Grayish-blue, translucent
Luster: Waxy to vitreous

Identified June 28, 2026More mineral →

Explore Chalcedony in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Grayish-blue, translucent; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed through the deposition of silica from aqueous solutions in volcanic cavities, sedimentary rocks, or hydrothermal veins. It often forms at relatively low temperatures near the Earth's surface.

Uses & applications

Used extensively in lapidary work for cabochons, beads, and carvings. Also historically used for making stone tools due to its conchoidal fracture, and currently for precision bearings and industrial abrasives.

Geological facts

Chalcedony is a broad term that includes sub-varieties like agate, onyx, and jasper. It has been used for seals and signet rings since the Bronze Age in the Mediterranean region.

Field identification & locations

Identify by its waxy luster, lack of visible crystals, and conchoidal (shell-like) fracture. It is commonly found in gravel beds, desert pavements, and within basaltic lava flows.