What it is confused with
Almost all black onyx is dyed chalcedony — a practice going back to Roman times — and black glass is common too.
Black, or black banded with white
Onyx crystals
Onyx is banded chalcedony, black, or black banded with white, rated 6.5–7 on the Mohs scale. Traditionally, it is linked to discipline, endurance and holding a boundary — attributed, not demonstrated.
- Mohs hardness
- 6.5–7 scratches window glass
- Crystal system
- Trigonal
- Pliny, AD 77
- Book 37.24 as “onyx”
- Main sources today
- Brazil also India, Madagascar
Pliny, Natural History, tr. Bostock and Riley.
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Properties
Composition
Banded chalcedony
Hardness (Mohs)
6.5–7
Crystal system
Trigonal
Color
Black, or black banded with white
Mined in
Brazil, India, Madagascar, USA
Worth knowing
Most solid black onyx is dyed gray chalcedony. Naturally uniform black onyx is scarce.
History
The Greek onyx meant fingernail — the pale banding reminded them of it.
Buying
Buying Onyx: fakes, value and treatments
What decides the price
Inexpensive; a uniform black and a high polish are what matter.
Where it is used
Cameos using its layers, men's rings and inlay.
A less familiar fact
"Onyx marble" used in architecture is banded calcite, a different and much softer stone.
Practical
Caring for Onyx
How to clean it
Warm soapy water and a soft cloth.
How to tell it is real
Nearly all solid black onyx is dyed gray chalcedony — industry norm, not a scam. Naturally uniform black onyx is genuinely scarce.
How hard is Onyx?
Onyx is banded chalcedony, tough for its hardness, which is why men’s rings are one of its main uses. A soft cloth and warm soapy water are all the care it needs.
Onyx, at 6.5–7, is harder than 19 of the other 42 stones here and softer than 15, with 8 level with it.
Primary source
What Pliny the Elder wrote about Onyx
“This name, though in some places given to a marble, is here used to signify a precious stone. Sudines says, that in this stone there is a white portion which resembles the white of the human-finger nail, in addition to the colours of chrysolithos, sarda, and iaspis.”
Pliny the Elder, The Natural History, translated by John Bostock and H. T. Riley (London: H. G. Bohn, 1855–57), book 37, chapter 24 — read the original text.
Onyx is Greek for fingernail, which is why Pliny’s sources compare its white band to a nail. He also notes that the name was given to a marble — the banded stone still sold as “onyx marble”. Who Pliny was and why we quote him →
Traditional associations
Onyx is traditionally linked to discipline, endurance and holding a boundary. Chakra in crystal practice: Root. Element: Earth.
Questions about Onyx
What is Onyx made of?
Banded chalcedony, crystallizing in the trigonal system.
Which month is Onyx the birthstone for?
Only as an alternative stone, for February.
Where does Onyx come from?
Brazil, India, Madagascar, USA.
Can Onyx be worn every day?
Yes, and it is easy to live with: at 6.5–7 on the Mohs scale, it is tough for its hardness and needs only warm soapy water.
Sources
Statements of fact on this page were checked against these sources in October 2026. How we choose and check sources: editorial policy.
Cite this page
AstroHot. “Onyx Crystals: Meaning, Hardness and Origins.” Accessed October 28, 2026. https://astrohot.com/crystals/gemstones/onyx/
For Wikipedia
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