mineral

Chalcedony (Common Opal variant or Chert/Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Yellowish-tan to translucent white; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.64

Hardness: 6
Color: Yellowish-tan to translucent white
Luster: Waxy to vitreous

Identified April 6, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica from groundwater in volcanic cavities, sedimentary rocks, or hydrothermal environments. It often precipitates at low temperatures in fissures or pockets.

Uses & applications

Used primarily in lapidary arts for cabochons, carvings, and beads. Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal edges.

Geological facts

This specimen shows the characteristic 'conchoidal fracture'—smooth, curved breaks similar to glass. Chalcedony is technically a fibrous cryptocrystalline form of quartz and moganite.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. It is common in riverbeds, desert pavements, and volcanic regions globally.

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