mineral

Botryoidal quartz (likely chalcedony or druzy quartz)

Silicon dioxide, SiO₂; microcrystalline quartz (chalcedony) with possible drusy quartz coating

AI-generated identification · may be incorrect

White, rounded grape-like aggregates with a sugary/vitreous sparkle; quartz hardness ~7 Mohs, no cleavage, conchoidal fracture, hexagonal crystal structure, and specific gravity about 2.65. The image alone cannot distinguish chalcedony from coated calcite or aragonite with certainty.

Identified August 11, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits successive rounded crusts in cavities and fractures, commonly in volcanic rocks; generally Cenozoic to older depending on host deposit.

Uses & applications

Used as a lapidary and collectible specimen; attractive pieces may be polished or mounted in jewelry, though this small sample has modest value.

Geological facts

“Botryoidal” describes its grape-like surface texture, not a separate mineral species; drusy surfaces consist of many tiny quartz crystals.

Field identification & locations

Common in geodes and volcanic cavities worldwide, including Brazil, Mexico, Uruguay, and the western United States. Quartz will resist a steel knife and should not fizz in dilute acid; calcite is softer and fizzes.