Chalcedony in Host Rock

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Pale blue to greyish-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Monoclinic (Cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & Geological History

Formed through the deposition of silica-rich fluids within cavities or fractures of host rocks (often volcanic or sedimentary) at relatively low temperatures. This specimen shows a thick vein or layer of chalcedony attached to a dark, fine-grained host rock.

Uses & Applications

Used primarily in lapidary arts for jewelry, cabochons, and ornamental carvings. Also collected as geological specimens in its raw form.

Geological Facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are so small they can only be seen under extreme magnification. Blue chalcedony was used in antiquity for Babylonian cylinder seals as early as 1800 B.C.

Field Identification & Locations

Identify by its waxy luster, conchoidal fracture (curved breaks), and hardness (it will scratch glass but cannot be scratched by a steel knife). Commonly found in geodes, volcanic gas bubbles (amygdules), and hydrothermal veins.

Identified on: 5/1/2026

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