mineral

Chalcedony (Common Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent grey, lavender, and tan; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Break: Conchoidal

Hardness: 6
Color: Translucent grey, lavender, and tan
Luster: Waxy to vitreous

Identified July 16, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Translucent grey, lavender, and tan; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Break: Conchoidal

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic and sedimentary rocks. This specimen appears water-worn, likely found in a riverbed or coastal area.

Uses & applications

Commonly used for lapidary work, jewelry making (cabochons), and as a collector's specimen. In industry, it can be used for mortars and pestles 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. When it exhibits banding, it is specifically called Agate.

Field identification & locations

Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. Common in volcanic regions and gravel deposits worldwide.