Onyx is a variety of gemstone that comes from Chalcedony – a silicate mineral, mostly made of calcite (similar to marble and granite), which usually features contrasting layers of colour.

Its stunning layers give it a strikingly dramatic look, which has understandably made it a go-to choice in jewellery making. Black onyx, in particular, is a hugely popular gemstone.

However, there’s so much to know about this amazing stone – including its different colours (yes, it’s not all about black onyx), its durability, its value and how to tell a real black onyx stone from the rest. Curious to learn more? Read on.

What does onyx look like?

Most people associate onyx gemstones with a jet black colour with some contrasting white layered bands. However, onyx is also found in brown, red and white variations. Brown and white onyx is usually referred to as sardonyx, while the red and white variation is recognised as cornelian onyx.

All forms of onyx gemstone feature multiple layers, with the lighter layer of stone sitting on top of the darker layer. This property has, historically, made onyx a popular stone to use for engraving techniques as well as producing cameos, where a raised relief is produced to form a design that is lighter than the layer it sits on.

What is onyx made of?

Onyx is naturally formed from calcite in caves or bedrock openings around the world. Calcite is the same mineral that makes up limestone, travertine and marble. When spring or groundwater featuring dissolved calcite in it drips and evaporates from the ends of stalagmites and stalactites. Once it evaporates, it leaves behind traces of minerals and calcium carbonate which causes its intricate bands of varying colours.

The bands of colour are produced with alternating silica minerals – quartz and morganite – and leave behind bands that lie parallel to one another. This tends to be why agate is often mistaken for onyx, as it is formed in the same way. However, the layers produced when agate forms are not parallel. Instead, the alternating bands are produced in a more dramatically curved formation.

Where does onyx come from?

Onyx is mined from several countries around the world including:

  • Afghanistan
  • Australia
  • Argentina
  • Brazil
  • Botswana
  • Canada
  • China
  • Czech Republic
  • France
  • Germany
  • India
  • Madagascar
  • Mexico
  • Pakistan
  • Russia
  • Serbia
  • The UK
  • Uruguay
  • Yemen

Onyx is also mined in some areas in the US.

Is onyx durable?

Onyx has a rating of 6.5 to 7 on the Mohs scale. So, it’s not the most durable gemstone out there, but it’s also not one of the most delicate either.

Here are some of onyx’s other properties: 

Chemical Formula:SiO2
Refractive Index:1.530-1.540

What is black onyx?

onyx gemstone

Black onyx is often the most well-known variation of the onyx gemstone. It’s a form of onyx that has a black base and white bands that sit parallel across the top surface of the stone.

People sometimes confuse it with agate due to its similar look. However, unlike black onyx, agate has curved bands, rather than parallel bands. Throughout history, it’s had a number of different meanings, from being seen as a stone that caused conflicts between friends to the more positive associations it has now – in providing protection and helping people to remain grounded, especially when used in feng shui.

What does raw black onyx look like?

Raw black onyx is usually not completely black. It can appear brown/greyish and sometimes dark green in colour when found in its natural state. But it appears black because it’s so deep in colour and opaque. That’s why a lot of jewelers tend to use a form of chalcedony that has been dyed black to get that deep, jet black that consumers are looking for, instead of slight hues of green and brown.

Raw black onyx is incredibly difficult to come by as it is a lot easier for suppliers to mine red and brown onyx and then dye it black. So be careful when it comes to buying onyx.

How to identify black onyx?

If buying real black onyx is a must for you, you’ll need to have the knowledge to differentiate between what’s real and what has been dyed black.

There are a number of methods you can use to identify whether you have the real thing or not, including:

  • the heat test – if it remains cool against your skin, it’s real.
  • the scratch test – use a safe material that’s under 6 on the Mohs scale to test its hardness, like a copper coin, your finger nail or a soft stone (fluorite, for example). Scratch the non-decorative side. If it’s real, it should blemish but not scratch.
  • the acid test – real onyx contains quartz, which will not react to many acids used for cleaning other rocks. So, it’s possible to drop your black onyx into muriatic or oxalic acid. If it fizzes or you start to see bubbles form, it’s not real.

However, if you don’t have the experience or feel comfortable to make out the difference between a real black onyx stone and one that has been treated, you may want to get in touch with an experienced gemologist to identify the stones for you.

In the industry many jewelers will use a dyed black agate stone or other common black stones such as black spinel, or jade and call it onyx. So, make sure that you trust your supplier’s knowledge, especially if using ethically sourced materials is a large part of how you work.

Does black onyx scratch easily?

No, it doesn’t scratch easily in normal circumstances. However, it can chip or crack if hit hard. With its rating of 6.5 – 7 on the Mohs scale, it’s certainly not the hardest stone around, but it is very durable.

Can black onyx go in water?

Yes, you’re perfectly safe to put black onyx in water – whether you’re wearing it in the shower or cleaning it.

It has a high tolerance, which makes warm water, mild soap and a soft brush ideal for regularly cleaning your onyx jewellery. You should avoid any ultrasonic or mechanical cleaning equipment. Once cleaned, you should simply allow it to air dry.

Is black onyx expensive?

Black onyx can be expensive. This is in part because due to genuine black onyx’s rarity and popularity. If you have a stone that’s been identified by a gemologist as being real, naturally occurring black onyx, it can be extremely valuable.

Dyed onyx is a very affordable alternative to work with. It can add a unique look to your designs without you having to source more valuable stones, such as black diamonds.

What is black onyx good for?

In the jewellery industry, black onyx is often used to create smooth cabochon stones for use in rings and pendants. Due to its smooth, glossy lustre, it’s a great stone to set with silver or gold pieces, and as it’s reasonably inexpensive to stock up on it makes for a popular choice among jewellers and consumers.

Where can I buy onyx stones?

Here, at Cooksongold! We have a range of pre-cut dyed onyx gemstones. With our pre-cut onyx stones, it’s simple to add them to your pendant, ring or bracelet designs.

Shop our varied sizes and shapes available in opaque black and with varying banding detail.

Want to add an intricate design to your setting too? Explore our range of gallery strip for a different take on your latest stone set designs.

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Author: Cooksongold
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