mineral

Tumbled blue-gray chalcedony (likely blue quartz or agate)

Microcrystalline quartz, SiO₂; likely chalcedony, possibly dyed

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent blue-gray color, waxy to vitreous luster, cryptocrystalline structure, no cleavage, conchoidal fracture; specific gravity about 2.58–2.64. The smooth spherical shape indicates tumbling and polishing.

Identified August 22, 2026More mineral →

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Physical properties

Formation & geological history

Chalcedony forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, commonly during the Cenozoic or older volcanic episodes. The blue coloration may be natural or enhanced by dyeing, a common treatment for tumbled stones.

Uses & applications

Used as a decorative tumbled stone, cabochon, bead, or inexpensive jewelry material; not generally used structurally.

Geological facts

Chalcedony is quartz whose crystals are too small to see individually. Blue-gray specimens can resemble dyed quartz, blue lace agate, or common glass, so laboratory testing may be needed for certainty.

Field identification & locations

Look for a waxy surface, translucency, conchoidal fracture, and inability to scratch it with a steel knife; it should scratch ordinary glass. Common sources include Brazil, Madagascar, India, Uruguay, and the western United States.