Mineral

Chalcedony (Botryoidal/Drusy Quartz)

Silicon Dioxide (SiO₂)

Hardness: 6.5-7 on Mohs scale; Color: Milky white, beige, semi-translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific gravity: 2.6-2.64.

Hardness: 6
Color: Milky white, beige, semi-translucent
Luster: Waxy to vitreous

Identified March 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich hydrothermal fluids in volcanic or sedimentary cavities (vugs). As the fluid cools or evaporates, it precipitates layers of microcrystalline quartz. The bumpy texture suggests a botryoidal or drusy formation.

Uses & applications

Used primarily for ornamental purposes, lapidary work (cabs), jewelry, and as a collector's specimen. It is also a source of silica in various industrial applications.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. Historically, it was used to create cylinder seals in Mesopotamia dating back to 2500 B.C.

Field identification & locations

Identify in the field by its waxy appearance, lack of cleavage, and ability to scratch glass. It often occurs as nodules or cavity linings in desert environments or volcanic basalt. Common in the Western US, Brazil, and India.

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