Chalcedony (Common Opal variant or Quartz)

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: White to translucent waxy grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.64

Formation & Geological History

Formed from the deposition of silica-rich water in volcanic cavities, sedimentary rocks, or hydrothermal veins. It typically forms at low temperatures near the Earth's surface.

Uses & Applications

Used primarily for jewelry (cabochons), carvings, healing stones in metaphysical practices, and historically for stone tools due to its sharp conchoidal edges.

Geological Facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without a microscope. It can technically be considered a variety of quartz.

Field Identification & Locations

Identify by its waxy luster, lack of visible crystals, and characteristic shell-like (conchoidal) fractures. Found worldwide, commonly in Brazil, India, and the Western United States.

Identified on: 4/17/2026

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