mineral

Botryoidal chalcedony (possibly agate/geode material)

Chalcedony, microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, translucent to opaque, tan-brown to gray, with waxy to dull luster and curved botryoidal surfaces. It lacks visible cleavage and consists of cryptocrystalline quartz, locally coated by drusy quartz or mixed with carbonate material.

Identified August 22, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles and precipitates in concentric, mammillary layers; later weathering can expose the nodules. The exact geological age cannot be determined from the image; occurrences range from volcanic rocks of many ages to sedimentary replacement deposits.

Uses & applications

Used as an ornamental stone, lapidary material, cabochons, carvings, and collectible specimens; attractive translucent pieces may be cut or polished.

Geological facts

Botryoidal means grape-like growth, produced by repeated silica deposition around a cavity or nucleus. The rough, nodular texture and possible drusy coating are characteristic of cavity-filling chalcedony.

Field identification & locations

Identify it by its curved growth forms, waxy appearance, conchoidal fracture, and hardness sufficient to scratch ordinary glass; acid testing can help detect any calcite matrix. Common in volcanic cavities and silica-rich sedimentary deposits worldwide.