mineral

Botryoidal Chalcedony (Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Creamy white to pale tan; Luster: Waxy to vitreous; Crystal structure: Hexagonal (trigonal) - microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific gravity: 2.58-2.64

Hardness: 6
Color: Creamy white to pale tan
Luster: Waxy to vitreous

Identified June 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous or sedimentary rocks. It often grows in rounded, grape-like clusters known as a botryoidal habit. This specimen appears to be a weathered nodule.

Uses & applications

Primary uses include lapidary work (cabs and beads), decorative ornaments, and specialized industrial abrasives or mortar and pestles due to its toughness. Highly valued by amateur rockhounds.

Geological facts

The term 'botryoidal' comes from the Greek word 'botrys', meaning a bunch of grapes. Chalcedony is a cryptocrystalline form of quartz, meaning its crystals are too small to be seen without high magnification.

Field identification & locations

Identify in the field by its waxy luster, hardness (it will scratch glass), and its characteristic rounded, bubbly surface texture. Commonly found in desert regions, volcanic ash beds, and river gravels.

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