mineral

Tumbled blue chalcedony (likely blue agate)

Microcrystalline quartz, SiO₂; chalcedony/agate variety

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; blue to gray-blue with darker banding, vitreous to waxy luster, cryptocrystalline structure, and no visible cleavage. The rounded, polished surface indicates a tumbled specimen; color may be natural or enhanced.

Identified September 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing microscopic quartz fibers in layers. Most specimens are Cenozoic to younger, commonly associated with basaltic volcanic terrains.

Uses & applications

Used for cabochons, beads, carvings, decorative stones, and inexpensive jewelry; attractive banded pieces are collectible.

Geological facts

Blue chalcedony is often confused with dyed agate, blue quartz, or polished slag glass. Strongly saturated blue color can indicate dye treatment.

Field identification & locations

Identify by its glassy/waxy luster, quartz hardness, conchoidal fracture, and lack of cleavage; it should resist scratching by a steel blade. Common sources include Brazil, Uruguay, India, Madagascar, Namibia, and the United States.