mineral

Botryoidal chalcedony (likely iron-stained agate)

Chalcedony, microcrystalline quartz (SiO₂), possibly with goethite/limonite inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; waxy to vitreous luster; gray-white, brown, and ochre coloration; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The rounded, grape-like surfaces are botryoidal, while brown coatings likely represent iron oxides.

Identified September 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic or sedimentary rocks, depositing successive layers of microcrystalline quartz; iron-bearing fluids create the ochre-brown coloration. Formation age depends on the host rock and cannot be determined from the image.

Uses & applications

Used as a lapidary and carving material, ornamental specimen, and occasionally in jewelry; attractive botryoidal pieces are mainly collector items rather than construction stone.

Geological facts

Botryoidal chalcedony can resemble botryoidal hematite, limonite, or polished slag; a quartz-rich interior and conchoidal fracture help distinguish it. Common sources include Brazil, Uruguay, Indonesia, Mexico, and the western United States.

Field identification & locations

Identify by its very high hardness, waxy surface, rounded growth forms, and inability to scratch with a steel knife easily; acid produces no reaction. The exact species should be confirmed by hardness, streak, and testing of a fresh surface.