gemstone

Black onyx or black agate cabochon

Cryptocrystalline chalcedony, SiO₂; likely black chalcedony/onyx, though dyed material is possible

AI-generated identification · may be incorrect

Polished opaque black-to-gray cabochon with vitreous-to-waxy luster and no visible crystal faces; Mohs hardness 6.5–7, conchoidal fracture, and specific gravity about 2.58–2.65. The mounted silver-colored ring and reflections obscure internal banding.

Identified September 15, 2026More gemstone →

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At a glance

Common name: Black onyx or black agate cabochon
Scientific name: Cryptocrystalline chalcedony, SiO₂; likely black chalcedony/onyx, though dyed material is possible
Category: gemstone
Identified: September 15, 2026
Method: Standard

AI Estimated Value

About $15–$75 for a typical silver ring with a commercial cabochon; roughly $100–$300+ for high-quality natural stone and substantial handmade metalwork.

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

Forms when silica-rich groundwater fills cavities or fractures, depositing microcrystalline quartz; geological ages vary widely, commonly Cenozoic to older volcanic-host-rock settings. Commercial black onyx is frequently dyed gray or pale chalcedony.

Uses & applications

Used for rings, cabochons, beads, carvings, and ornamental objects; valued mainly for polish, color, pattern, and craftsmanship rather than rarity.

Geological facts

“Onyx” technically refers to banded chalcedony, while uniformly black material is usually called black chalcedony or commercial black onyx. A dye concentration along surface cracks or around drill holes suggests treatment.

Field identification & locations

Common sources include Brazil, Uruguay, India, Mexico, Madagascar, and the United States. Verify with a loupe, streak test on unglazed porcelain, and disclosure from the seller; avoid damaging tests on jewelry.