mineral

Tumbled blue chalcedony (likely blue agate)

Microcrystalline quartz, SiO₂; chalcedony with possible agate banding

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; blue to gray-blue color, waxy-to-glassy luster, cryptocrystalline quartz, no visible cleavage, and specific gravity about 2.6. The rounded polished surface and pale orbicular/banded area are characteristic of tumbled chalcedony or agate.

Identified September 13, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing microscopic quartz fibers and sometimes concentric bands over long periods, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and polished specimens; durable enough for jewelry but generally modestly priced.

Geological facts

Blue chalcedony may owe its color to trace minerals, microscopic inclusions, or light-scattering effects; intense uniform blue color can sometimes indicate dye treatment.

Field identification & locations

Identify by its hardness, waxy appearance, translucent edges, and lack of cleavage; it commonly occurs in volcanic regions, especially Brazil, Uruguay, India, Madagascar, and the western United States. A scratch test with steel should not readily mark it.