mineral

Botryoidal iron-stained quartz/chalcedony

Microcrystalline quartz (SiO₂), likely chalcedony with limonite/goethite coatings

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-white to brown, waxy to dull luster, botryoidal/radiating microcrystalline texture, and no prominent cleavage. The brown coloration is likely iron-oxide staining; specific gravity is approximately 2.6.

Identified September 10, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited successive rounded crusts in cavities, fractures, or replacement zones, with later oxidation producing limonite/goethite. It may occur in volcanic or sedimentary rocks of widely varying ages.

Uses & applications

Used mainly as a collector specimen; comparable chalcedony is used for carvings, cabochons, abrasives, and decorative stone. Jewelry value depends on translucency, pattern, polishability, and rarity.

Geological facts

The grape-like rounded form is called botryoidal texture, produced by concentric mineral growth rather than individual large crystals.

Field identification & locations

Identify by its very hard, glass-scratching surface, waxy appearance, curved botryoidal surfaces, and lack of cleavage; acid should not fizz. Common in volcanic cavities and hydrothermal veins worldwide, including Brazil, Uruguay, Mexico, and the western United States.