Chalcedony (Quartz Var.)

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: White, cream, tan with pinkish iron staining; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Monoclinic (Microcrystalline); Cleavage: None; Fracture: Conchoidal to splintery.

Formation & Geological History

Formed through the deposition of silica-rich groundwater in the cavities or fractures of igneous or sedimentary rocks. It often grows in botryoidal (grape-like) clusters or as massive nodules.

Uses & Applications

Abrasives, semi-precious gemstones for jewelry (when polished), lapidary art, and popular among mineral collectors for its varied forms.

Geological Facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope. Agate and Carnelian are both varieties of chalcedony.

Field Identification & Locations

Identify by its waxy appearance, smooth conchoidal fractures, and hardness (it will scratch glass). Commonly found in dry riverbeds, volcanic ash deposits, and eroded limestone areas.

Identified on: 4/20/2026

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