mineral

Chalcedony (likely iron-stained agate)

Microcrystalline quartz, SiO₂ (chalcedony/agate)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, honey, and reddish-brown colors with waxy to vitreous luster. Quartz is trigonal, but chalcedony consists of microscopic intergrown fibers and typically lacks visible cleavage; density is about 2.58–2.64.

Identified August 9, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rock, precipitating as fibrous quartz; iron oxides create the red-brown coloration. The specimen’s exact age depends on its host rock, commonly ranging from Paleozoic to Cenozoic.

Uses & applications

Used for cabochons, carvings, beads, ornaments, and lapidary material; attractive banded varieties are sold as agate. Rough common pieces generally have modest value.

Geological facts

Its granular, weathered outer rind and waxy translucent interior are typical of silica replacement or cavity filling. It may resemble jasper, but chalcedony is generally more translucent and can scratch glass.

Field identification & locations

Common in volcanic terrains and silica-rich veins worldwide, especially Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Field confirmation: glass-scratching hardness, conchoidal fracture, and no fizz with dilute acid; laboratory testing is needed for certainty.