mineral

Tumbled chalcedony (likely milky quartz)

Chalcedony, cryptocrystalline SiO₂; possibly quartz-rich chert

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; pale white to gray with faint blue or brown zones, waxy to dull luster, translucent edges, and no visible cleavage. It appears naturally microcrystalline and has a typical quartz-like specific gravity near 2.6.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits microscopic quartz fibers in cavities, fractures, or sediment; the material may be Paleogene to Recent depending on locality. This specimen has been rounded and polished by tumbling.

Uses & applications

Used for carvings, cabochons, beads, decorative stone, and lapidary work; higher-quality colored chalcedony is collectible, while pale material has modest value.

Geological facts

Chalcedony is a broad gemological term that includes varieties such as agate, carnelian, chrysoprase, and onyx. Its subtle translucency and waxy appearance distinguish it from ordinary opaque quartzite.

Field identification & locations

Commonly found in volcanic cavities, silica-rich sedimentary rocks, and gravel deposits worldwide, especially Brazil, Uruguay, India, Madagascar, and the western United States. A glassy luster, conchoidal fracture, and hardness sufficient to scratch ordinary glass support identification.