mineral

Chalcedony (Common Opal variant or Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: waxy white, translucent grey, or bluish; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7.

Hardness: 6
Color: waxy white, translucent grey, or bluish
Luster: Waxy to vitreous

Identified April 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the precipitation of silica-rich groundwater in the cavities of volcanic or sedimentary rocks. It often occurs in hydrothermal veins or as nodules in limestone.

Uses & applications

Used widely in semi-precious jewelry (beads, cabochons), ornamental carvings, and historical stone tools (due to its sharp conchoidal fracture).

Geological facts

Chalcedony is a cryptocrystalline form of silica. If it shows banding, it is called Agate; if it is opaque and reddish, it is Jasper. Archaeologists have found chalcedony seals dating back to the Bronze Age on Crete.

Field identification & locations

Identify in the field by its waxy appearance, smooth conchoidal (shell-like) fracture edges, and its ability to scratch glass. It is commonly found in desert regions or near volcanic ash deposits.

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