mineral

Botryoidal Chalcedony (Agate/Chert Nodule)

Chalcedony (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Typically gray, blue, white, or brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Typically gray, blue, white, or brown
Luster: Waxy to vitreous

Identified March 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. The 'bumpy' botryoidal (grape-like) texture occurs as mineral layers grow outward from multiple points of nucleation simultaneously.

Uses & applications

Used primarily for jewelry (cabochons), ornamental carvings, and as decorative mineral specimens for collectors. In industry, high-purity chalcedony can be used as an abrasive.

Geological facts

The term 'botryoidal' is derived from the Greek 'botrys', meaning a bunch of grapes. Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope.

Field identification & locations

Identify in the field by its waxy luster, hardness (it will scratch glass but not quartz), and its characteristic rounded, bulbous surface. It is commonly found in desert regions, volcanic ash beds, and river gravels.

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