mineral

Tumbled blue chalcedony (likely agate or common opal)

Microcrystalline quartz, SiO₂; possibly hydrated silica opal, SiO₂·nH₂O

AI-generated identification · may be incorrect

Smooth, rounded, pale blue-gray, translucent, and waxy to glassy; chalcedony has Mohs hardness 6.5–7, while opal is 5.5–6.5. Quartz varieties are trigonal cryptocrystalline and lack visible cleavage; opal is amorphous.

Identified August 15, 2026More mineral →

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At a glance

Common name: Tumbled blue chalcedony (likely agate or common opal)
Scientific name: Microcrystalline quartz, SiO₂; possibly hydrated silica opal, SiO₂·nH₂O
Category: mineral
Identified: August 15, 2026
Method: Standard

AI Estimated Value

Approximately $2–$15 for a common tumbled stone; $20–$100+ if it is confirmed natural blue chalcedony, high-quality agate, or attractive opal.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Chalcedony forms when silica-rich groundwater fills cavities and fractures, often in volcanic rocks; opal forms from hydrated silica gels. Precise age and identity cannot be determined from the photograph.

Uses & applications

Used for inexpensive jewelry, cabochons, beads, carvings, and collectors’ specimens; industrial chalcedony is occasionally used as a silica source.

Geological facts

The uniform rounded shape and polished surface indicate human tumbling. Blue coloration may be natural, dyed, or enhanced, and color alone cannot reliably distinguish chalcedony from opal.

Field identification & locations

Common sources include Brazil, Uruguay, Madagascar, India, Mexico, and the western United States. A scratch test, specific-gravity test, and close inspection for banding or play-of-color can help; avoid scratching valuable pieces.