What is chalcedony?
By Jared James · Last updated 21 May 2026
Definition
Chalcedony is a variety of quartz with a microcrystalline structure, meaning its crystals are too small to see individually, giving it a smooth, waxy or silky appearance rather than the visible crystal faces of larger quartz. It covers a huge family of stones: agate, carnelian, onyx, jasper, chrysoprase and bloodstone are all forms of chalcedony. In its pure form it is usually grey to pale blue, translucent, and very receptive to polishing, which is why it has been prized for seals, intaglios and cabochons since antiquity.
Frequently asked questions
- What is the difference between chalcedony and agate?
- Agate is a type of chalcedony, specifically the banded form that shows layered colours or patterns. Plain chalcedony is uniform in colour with no distinct banding. All agates are chalcedony, but not all chalcedony is agate.
- What colour is chalcedony?
- On its own, chalcedony is typically pale grey, white or milky blue. When mineral impurities are present during formation it takes on other colours: iron creates the reds and oranges of carnelian, nickel produces the apple green of chrysoprase, and layering creates the blacks and whites of onyx.
- Is chalcedony durable enough for everyday jewellery?
- Yes, it is a practical stone for everyday wear. Chalcedony measures 6.5 to 7 on the Mohs hardness scale, making it tough enough for rings, bracelets and pendants, and it does not need special care beyond keeping it away from harsh chemicals.
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