Black onyx is a stunning mineral, often carved into gemstones or decorative jewellery with intricate patterns and a smooth, shining lustre. It is easy to see why people have admired and traded onyx for centuries, in many different areas of the world.
Onyx is a beautiful and versatile mineral that can also be used for carvings and sculptures – there are a great many examples of these throughout history.
Perhaps you have an onyx piece and you are curious to find out whether it is real onyx or not? Maybe you have inherited a specimen and you are wondering how much you can sell it for? Or you might be interested in precious stones and want to find out more? We will provide you with 6 simple steps that can be taken to identify whether you piece of onyx is genuine or not.
In summary, you can look at the surface texture, feel the weight, test the hardness, investigate the price and chemical formula, and as a last resort use a hammer. Becoming knowledgeable about this intriguing mineral is another weapon you can arm yourself with in the quest to identify real onyx.
What Is Black Onyx?
Before finding out how to positively identify whether your onyx is real or not, it can be very valuable to learn more about this eye-catching mineral.
If we want to get technical for a moment, black onyx is a type of chalcedony – a silicate mineral (made up of groups of silicates, or in other words anions containing the elements silicon and oxygen). The chemical formula of onyx is therefore silicon dioxide, SiO2. To be specific, onyx is the parallel-banded variety of chalcedony, containing bands with alternating colors.
The bands of onyx can range in colour but the most common specimens available to buy are black and white. You may hear other minerals being called onyx mistakenly, usually referring to parallel-banded varieties of minerals like marble and opal.
The word ‘onyx’ comes from a Greek word which translates as ‘claw’ or ‘fingernail’. This is supposedly because varieties of white or flesh-colored onyx can resemble a human fingernail. Onyx can mostly be found naturally in Brazil or India. There are also large deposits in Pakistan, Germany and Yemen. An onyx deposit can usually be found in caves, it is formed where water which is rich in silica drips slowly through fissures in surrounding rocks. Here is an example of a cave full of onyx (not the black variety!) in Bulgaria.
What Is Black Onyx Used For?
As indicated by the origin of the word onyx, the history of the human-use of this gemstone goes back to Ancient Greece. It was also widely traded throughout Persia, China and India, and valued by the Romans. Most often onyx has been used in jewellery, but another common use throughout history was in carvings and sculptures depicting people, objects, scenery, detailed patterns, and even scenes of myths, legends and folklores.
Nowadays it is common for onyx to be used as an accent stone – a stone which complements or helps other stones like rubies stand out. It is set into rings and necklaces, and even watch faces. It is also commonly sold as a small gemstone in crystal shops, and can hold deep meaning for some people.
Black Varieties Of Onyx
Nicolo onyx is one variety with a super thin layer of white, semi-translucent, which can even appear as a blue shade against a black background. This can occur where an artist has carved a cameo (bas-relief carving where the pattern subtly stands out from the background) or intaglio (a subtle type of carving or engraving) from the onyx.
Arabic onyx, also known as true onyx, is the name given to onyx specimens with a clear black lower layer and a strongly contrasting white upper layer. The history of the name of this variety of onyx is unclear, and interestingly onyx in Arabic language is ‘el jaza’ which means sadness.
Although it is possible to find a band of onyx naturally which is thick enough to cut and produce specimens colored totally black, it is very rare. Nowadays many gemstone sellers will dye a chalcedony black and sell it as black onyx. It is also possible that sellers will dye other minerals black, usually similar quartz-type minerals, and brand them as onyx. They may also use plastic or resin to imitate the precious black mineral, and this is an increasing problem. Many unwitting buyers are tricked into buying fake onyx at a low cost for the buyer but a big profit for the seller.
Therefore, if you have some onyx and you want to tell whether it is real or not, there are some simple steps you can follow to get a positive ID.
How To Tell If Black Onyx Is Real
There is an easy process you can follow in the quest to find out if your onyx is real, genuine onyx or not. It is important to use these steps in combination, because no step alone can give you a positive onyx ID. Follow these steps and satisfy your curiosity:
1. Surface texture
First of all, what does the surface look like? Many onyx pieces will have black and white alternate banding, even if the layer appear very faint. But this can depend on the size of the piece and the way it has been worked.
Fake onyx often has a glassy shine to it. Whereas real onyx will have an almost waxy lustre and may appear glossy if it has been polished. Other features to look out for are an opaque transparency, and possibly a reflective façade. It most certainly should not have a foggy look, or sport any scratches or cracks in the surface. A little confusing, right? To the untrained eye it can be hard to tell fake onyx from real onyx just based on the surface texture. So let’s try another step to gain a bit more information.
Black onyx is a fairly dense mineral and can have a pleasant, weighty feel when held in the hand. A quick feature that will discount your onyx specimen as real onyx is if it feels suspiciously light when held in the hand. If this is the case, it is most likely made from plastic. However, some of the best fake onyx is made from resin, and can contain materials that give the specimen a weighted feel. So weight alone cannot be used as an indicator.
3. Hardness – The Scratch Test
How hard does it feel? True onyx is rated as 6-7 on the Moh’s scale of hardness. This is pretty high up, and is classified in this way because the surface can be scratched by a steel nail. Onyx imitations like plastic and resin materials will be much softer and easier to scratch.
To test this out you can first use your fingernail – does it scratch easily with just a fingernail? It is definitely not onyx then. If this doesn’t make a mark, you can upgrade to a coin. Try scratching the surface of your piece with the edge of a coin. If it is a decorative piece you may want to try a test area on the back or underside where scratches will not be seen. Does it scratch easily with just a coin? Again, it is not onyx.
If neither of these scratched the surface you can try a standard kitchen knife – but please handle with care! If the surface still cannot be scratched with a knife, this is a good sign and you may have real onyx in your hand.
It is good to note here that real onyx can be scratched by materials harder than 7 on the Moh’s scale. This includes even harder stones like diamonds. So a good tip, if you possess a number of precious stones, is to keep harder stones away from onyx to prevent scratching.
Another good indicator of real onyx can be the price. How much did you purchase your onyx for? Price will, of course, be affected by other features for example if the onyx has been set in gold, and the size of the specimen, so it is worth bearing this in mind.
Onyx can be valued by the carat, just like gold. In 2021, natural black onyx was valued at $40 USD per carat of onyx. Synthetic onyx was being sold for around $6 USD per carat. However, very small specimens which possess low quality carat could be priced around $5 USD per carat. Larger specimens of higher quality carat could cost even more than $600 USD per carat!
One good tip in terms of price is to look up other similar items to yours, and see what the going rate is. Make sure to find reliable sources of information and sellers with high ratings and professional backing.
5. The Chemical Formula
When buying precious stones, the chemical formula of the stone can be displayed in the description to ensure correct identification. The chemical formula of onyx is silicon dioxide, SiO2, so this can be a good sign if it is displayed with the piece. However, it is important to bear in mind that quartz and some other silicate minerals can have the same, or very similar chemical formulas as they all contain a combination of silicon and oxygen in one form or another.
6. Last Resort – Use A Hammer!
Please note, this is the last step on our list for a reason – it requires destruction of you precious onyx piece! This is only recommended if you have several very small pieces of supposed onyx, like small beads, and can afford to smash one of them to help you in your true onyx quest.
But wait, just before you smash that bead up, check around the hole through the centre of the bead (if it has one). If there is some kind of dimpling around the hole, it is very likely your bead is black glass rather than onyx. This feature can save you from destroying your bead!
If you really need to know and can afford to waste a small piece of potential onyx, you can place it inside a bag, or place a form of covering over the top. Put the bead and covering on a safe surface, grab a hammer and give it a gentle tap – just enough to break it apart. If your smashed pieces are shiny on the inside they are made from glass. If they are dull where they have broken, it is likely you have onyx.
How Can You Tell Black Onyx Apart From Glass?
Black glass is a very convincing onyx imitator. One way to tell the difference between these materials is to place the piece on your lips and leave it there for a few seconds. If it begins to feel fairly warm after a few seconds it is likely to be glass rather than onyx, as glass is a better heat conductor.
As mentioned in the last step, if you have onyx beads or an onyx piece containing a hole, if there are dimpling marks around the hole this is another indication it may be glass.
How Should You Care For Black Onyx?
When not wearing or displaying your onyx piece, it is good practice to store it away in a box or pouch. It is important to keep is separate from those materials with a higher Moh’s scale rating (find out more about this scale here). Ensure your piece is not exposed to harsh chemicals, and keep it clean. This will preserve its lustre, and help to maintain it perfectly for a great number of years.
Does Black Onyx Have A Meaning Or Symbolism?
It is widely believed that black onyx can be useful for people who find it difficult to sleep, or who are going through a stressful period of their lives. Some believe the smooth, regular banding of onyx helps to soothe your mind and bring you peace. It may help to ground and balance you, and has been used in many cultures as a protective talisman.
What Does Black Onyx Mean In Different Cultures?
For Romans, carving an image of the Roman god Mars (god of war) was believed to help soldiers going into battle.
A widespread belief in the Middle East was that black onyx could dispel arguments and negative emotions, especially when rubbed between your fingers.
Similarly, in Indian culture the dark colour of black onyx was believed to absorb negative feelings and incidents, leaving the bearer lightened.
Some people believe that having black onyx in your home can improve the Feng Shui by protecting against negative energies and helping with self-control.