mineral

Chalcedony (Botryoidal Agate vein)

Chalcedony (Microcrystalline Quartz) - SiO2

Hardness: 6.5–7 (Mohs scale); Color: White, translucent, to grayish; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (Trigonal) microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: White, translucent, to grayish
Luster: Waxy to vitreous

Identified February 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed by the deposition of silica-rich hydrothermal fluids in rock cavities or fractures. It often grows in botryoidal (grape-like) or banded layers over thousands of years within volcanic or sedimentary host rocks.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), and as a decorative collector's specimen. Historically used for making tools and seals due to its toughness.

Geological facts

This specimen displays 'botryoidal' growth, which is a habit where the mineral forms rounded, globular masses. Agate and chalcedony are technically the same mineral, with agate referring specifically to the banded or variegated varieties.

Field identification & locations

Identify in the field by its waxy luster, translucency, and the fact that it cannot be scratched by a steel knife. Common in desert environments and volcanic regions like the American Southwest and Brazil.

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