mineral

Botryoidal chalcedony (possibly quartz geode coating)

Microcrystalline quartz, SiO₂; botryoidal chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; cream to tan, waxy-to-dull luster, translucent edges, and rounded grape-like aggregates. It has no obvious cleavage, conchoidal fracture, and typically a specific gravity near 2.6.

Identified September 6, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits layers of microcrystalline quartz in cavities, commonly in volcanic rock; the specimen appears partly weathered or broken from its host. Such deposits may range from Cenozoic to much older, depending on locality.

Uses & applications

Used as an ornamental and lapidary material, in carvings, cabochons, and mineral collections; less suitable for structural construction.

Geological facts

The rounded “grape” texture is called botryoidal, from Greek meaning grape-like. The cavity and layered coating may indicate a geode or vesicle lining.

Field identification & locations

Identify by its bulbous aggregates, waxy appearance, quartz hardness, and lack of cleavage; a steel knife should not easily scratch it. Common sources include Brazil, Uruguay, Mexico, Morocco, and the western United States.