mineral

Tumbled gray-blue chalcedony (likely blue quartz or common opal)

Chalcedony, microcrystalline SiO₂; exact identification requires testing

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs for chalcedony (lower if opal), translucent blue-gray body, vitreous to waxy luster, no visible cleavage, cryptocrystalline structure, and specific gravity roughly 2.58–2.65. The smooth rounded form 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, commonly in volcanic rocks; opal forms similarly at lower temperatures. Formation ages vary from recent deposits to ancient volcanic sequences.

Uses & applications

Used for cabochons, beads, carvings, and decorative objects; common tumbled specimens have modest value.

Geological facts

Blue-gray coloration may result from microscopic inclusions or light scattering; a refractive index, hardness, and specific-gravity test would distinguish chalcedony from opal or glass.

Field identification & locations

Likely chalcedony if it scratches glass and feels relatively dense; opal is softer and typically has a more waxy appearance. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.