mineral

Chalcedony (specifically Common Opal or Agate variant)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Waxy white to translucent grey with yellow/brown iron inclusions; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64

Hardness: 6
Luster: Vitreous to waxy

Identified March 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in the cavities of igneous rocks or sedimentary layers. Found in volcanic environments ranging from the Cenozoic to recent times.

Uses & applications

Used primarily in lapidary work for cabochons, beads, and carvings. Also used historically for tools due to its sharp conchoidal fracture and in modern industrial abrasives.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a standard microscope. It has been used since the Bronze Age for making cylinder seals in Mesopotamia.

Field identification & locations

Identify in the field by its waxy luster and smooth, curved (conchoidal) break surfaces. Commonly found in riverbeds, desert pavements, and volcanic regions like Oregon, India, and Brazil.