What is black onyx?
Black onyx is the solid-black form of onyx, which is a banded variety of chalcedony (a microcrystalline form of quartz, silicon dioxide, SiO2). True onyx has straight, parallel bands, traditionally black and white, but the stone most people mean by "black onyx" is a uniform, glossy black. It has a Mohs hardness of 6.5 to 7, takes a beautiful high polish, and creates a strong contrast against metal and lighter stones, which is why it is a classic jewellery stone for both men and women.
This guide explains what black onyx really is, the important point that most of it is dyed, how it differs from black obsidian, its long history in jewellery, and how to choose and care for it.
Physical properties at a glance
- Mineral: Chalcedony (microcrystalline quartz, SiO2), the onyx variety
- Colour: Solid, uniform black (black and white when naturally banded)
- Mohs hardness: 6.5 to 7, durable for all jewellery
- Lustre: Vitreous, takes a high polish
- Transparency: Opaque
- Common treatment: Most solid-black onyx is dyed grey chalcedony, a stable, centuries-old practice
- Main sources: Brazil, India, Madagascar and others
An important point: most black onyx is dyed
This is the single most useful thing to know. Natural, evenly solid-black chalcedony is uncommon, so the vast majority of black onyx on the market is grey or banded chalcedony that has been dyed black. The technique is genuinely ancient, the Romans were already treating chalcedony with sugar and acid to deepen the colour, and the dye is stable and permanent. So "dyed" here does not mean fake or low quality; it is the normal, accepted way black onyx is produced. It is simply useful to know that the deep even black is a treatment, not usually a natural colour. Reputable sellers treat this as standard, and the stone is still genuine chalcedony.
Black onyx vs black obsidian vs black agate
These three black stones are often mixed up, even on shop labels. Here is the simple difference:
In short: onyx and black agate are both chalcedony (the difference is straight vs curved banding, and the terms are often used interchangeably), while obsidian is volcanic glass and is softer. If a "black onyx" piece is very glassy with sharp chipped edges, it may actually be obsidian. Compare with our black obsidian collection.
Shop black onyx at Crystals Healing UK
Black onyx bracelets, necklaces and tumbled stones, handmade in the UK with free delivery on orders over £30.
Shop black onyx Men's jewelleryA long history in jewellery and carving
Onyx has been a prized jewellery and carving stone for thousands of years. Its naturally straight black-and-white banding made it the ideal material for ancient Greek and Roman cameos and intaglios, where carvers cut through a pale layer to reveal the dark layer beneath, creating a raised two-colour portrait. Sardonyx (onyx with reddish-brown bands) was especially prized for Roman seal rings. In the 19th century, solid black onyx became closely associated with Victorian mourning jewellery, worn during periods of grief, and it remains a classic, elegant black stone today. These long traditions are where its cultural associations with steadiness and solemn elegance come from.
Black onyx in jewellery and pairings
At Mohs 6.5 to 7 with a deep even colour, black onyx is versatile and hard-wearing. Its neutral black suits any outfit and is a staple of men's jewellery. It pairs especially well with:
- Hematite: metallic grey alongside matte or glossy black, a smart, masculine look. See our hematite and onyx bracelet.
- Tiger's eye: warm golden brown against black. See our onyx and tiger's eye bracelet.
- Black tourmaline: tonal all-black combination. See our onyx and tourmaline bracelet.
- Clear quartz or white stones: high-contrast black and white, classic and clean.
For a single statement piece, see our black onyx pendant necklace.
How to care for black onyx
- Water: black onyx (Mohs 6.5 to 7) tolerates a brief rinse, then drying. Because it is dyed, avoid prolonged soaking and salt water.
- Chemicals: keep away from harsh cleaners, perfume and cosmetics, which can affect the polish and dye over time.
- Scratches: store separately from harder stones, and put jewellery on after skincare and fragrance.
- Polishing: wipe with a soft cloth to keep the glossy black surface looking its best.
For which stones tolerate water, see our water-safe crystals guide.
Frequently asked questions
What is black onyx?
Black onyx is the solid-black form of onyx, a banded variety of chalcedony (microcrystalline quartz, SiO2). It has a Mohs hardness of 6.5 to 7 and is a classic, hard-wearing jewellery stone. Most solid-black onyx is dyed.
Is black onyx dyed?
Usually, yes. Naturally solid-black chalcedony is uncommon, so most black onyx is grey chalcedony dyed black. This is a stable, centuries-old practice and the stone is still genuine chalcedony, not an imitation.
What is the difference between black onyx and black obsidian?
Black onyx is chalcedony, a crystalline quartz (Mohs 6.5 to 7), usually with an even, smooth polish. Black obsidian is natural volcanic glass, softer (Mohs 5 to 5.5), with a very glassy look and sharp conchoidal fractures. Obsidian is natural black; onyx is usually dyed.
What is the difference between onyx and agate?
Both are banded chalcedony. Onyx has straight, parallel bands, while agate has curved, concentric bands. In practice the terms are often used interchangeably for black stones.
Can black onyx go in water?
Briefly, yes. It is Mohs 6.5 to 7, so a quick rinse and dry is fine, but because it is dyed, avoid prolonged soaking, salt water and harsh chemicals.
Is black onyx good for men's jewellery?
Very much so. Its deep, neutral black and durability make it one of the most popular stones for men's bracelets and necklaces, especially paired with hematite or tiger's eye.
Related reading
- Water-Safe Crystals: what can go in water and what to avoid
- Crystal Jewellery Guide: types, meaning and how to choose
- Crystals for Beginners: how to choose, use and care
Shop & downloads
- Black Onyx Crystals and Men's Crystal Jewellery
- Crystal Bracelets and Crystal Necklaces
- Crystal Gifts and New Arrivals
- Free Crystal Care Checklist (PDF) and Water-Safe Crystals Quick Chart (PDF)
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