mineral

Tumbled gray chalcedony (likely agate or quartzite)

Microcrystalline quartz, SiO₂ (chalcedony)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; smooth, rounded, gray-blue body with a waxy to vitreous luster and no visible cleavage. The polished surface obscures crystal structure; specific gravity is about 2.6.

Identified September 7, 2026More mineral →

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Physical properties

Hardness 6.5–7 Mohs; smooth, rounded, gray-blue body with a waxy to vitreous luster and no visible cleavage. The polished surface obscures crystal structure; specific gravity is about 2.6.

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures in volcanic rock, precipitating cryptocrystalline quartz over millions of years, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used as a lapidary stone for tumbled stones, cabochons, carvings, and jewelry; also collected as a decorative mineral.

Geological facts

Chalcedony is quartz made of microscopic interlocking crystals, so it lacks the obvious crystal faces of ordinary quartz. Gray varieties may be called flint, agate, or jasper depending on banding, opacity, and impurities.

Field identification & locations

Identify it by its glass-scratching hardness, waxy appearance, conchoidal fracture, and lack of cleavage; agate would show internal bands, while quartzite has a granular texture. Common sources include Brazil, Uruguay, India, Madagascar, and the western United States.