A market-wide average across qualities and sizes. Your stone's value depends on carat, color, clarity, cut, treatment, and origin.
Onyx, in strict gemological terms, is a variety of chalcedony characterized by straight, parallel bands of contrasting colors, typically black and white. In modern trade, the term 'onyx' is often used more loosely for solid black chalcedony, much of which is dyed. With Mohs hardness around 6.5–7 and good toughness, onyx is suitable for intaglios, cameos, cabochons and beads.
Market averages will not price your stone. GemstoneAI identifies gems and jewelry from a photo, checks authenticity and treatment signals, and gives you a real market valuation in seconds. Free to try.
The GemstoneAI market index for onyx is $5.35 per carat as of 2026-08-04. That is a market-wide average across qualities, not a quote for a specific stone. Individual value depends on carat, color, clarity, cut, treatment, and origin.
Visual tests alone are unreliable. GemstoneAI analyzes a photo of your stone for identity, treatment indicators, and authenticity signals, then estimates market value. It is free to try.
Over the past 30 days the onyx index moved +7.0%. Gem prices move on supply, demand, and metal markets; treat any single stone as a collectible first and an asset second.