How To Tell If Black Onyx Is Real

by Ultimate Jewelry Guide
How To Tell If Black Onyx Is Real

Black onyx is a beautiful mineral that may be carved into exquisite gemstones or ornamental jewelry. It is not hard to see why onyx has been prized and sold for so long in many different parts of the world.

There are several historical examples of onyx carvings and sculptures because of the mineral’s beauty and versatility.

Maybe you have a piece of what you think might be onyx, but you want to make sure. Maybe you’re curious about the market value of a specimen you inherited. Perhaps you’re curious about gemstones and want to learn more. The authenticity of your onyx may be determined in a few easy ways, which we will detail for you.

What Is Black Onyx?

It is helpful to gain a deeper understanding of onyx before determining its authenticity.

To go scientific for a second, black onyx is a form of chalcedony, which is a silicate mineral composed of groups of silicates, or anions, containing the elements silicon and oxygen. Because of this, silicon dioxide (SiO2) is the correct chemical formula for onyx. Onyx, a specific type of chalcedony, is distinguished by its parallel bands of alternate hues.

The onyx bands can be any color, although black and white are the most commonly found stones. It’s not uncommon for parallel-banded minerals like marble and opal to be incorrectly referred to as onyx.

Onyx is derived from the Greek word for “claw” or “fingernail,” which is where the English word “onyx” finds its origin. It is because some white or flesh-colored onyx forms look like human fingernails. The majority of onyx comes from mines in either Brazil or India. Large deposits can also be found in Germany, Yemen, and Pakistan. Onyx deposits are typically discovered in caves because this is where water rich in silica forms over time by gently dripping through cracks in the surrounding rocks.

How To Know If Your Black Onyx Is Real?

You can follow a simple guide to determine whether your onyx is authentic. No single method can guarantee a successful identification of a genuine black onyx. Thus, it’s vital to employ all of the methods together. If you’re curious, here’s what to do about it:

Examine The Surface Texture

Let’s start with the obvious question: how does the exterior appear? Onyx is common to have black and white alternating banding, even if the layer is quite light. However, this can vary depending on the size and processing of the object.

Many imitations of onyx have a glassy sheen. Onyx that has been polished will have a waxy sheen and may appear shiny, while imitations will not. Also potentially alarming is a reflective exterior or opaque transparency. It should not appear hazy or have surface flaws like scratches or fissures. Confusing, right? It can be difficult for the untrained eye to distinguish between genuine and imitation onyx based on surface roughness. Let’s take another stab at it then, shall we?

Check The Weight

Black onyx, a moderately solid mineral, can feel satisfyingly hefty when held in hand. If your onyx specimen seems unusually light when you hold it, that’s a red flag that it’s not the genuine article. Therefore, if this is the case, it is probably constructed of plastic. However, the most convincing imitations of onyx are often cast in resin and filled with ingredients that make the piece feel substantial to the touch. Therefore, it is not possible to utilize weight as a sole criterion.

Do The Scratch Test

Real onyx has a hardness of 6-7 on the Mohs scale. Given that a steel nail will leave a visible mark on the surface, this is considered very high quality. Material substitutes for onyx, such as plastic and resin, will be softer and more easily scratched.

The first thing you may do is scratch it with your fingernail to see whether it holds up. Then it is most assuredly not onyx. If this fails to leave a clear mark, try a coin. The edge of a coin can be used to scratch the surface of your black onyx. If you are concerned about visible scratches, try a small area on the underside or back of the item first. Is it easy to scratch with just a coin? Once again, it’s not onyx.

If neither works, you can always use a regular kitchen knife with caution. You may have genuine onyx in your hands if a knife cannot scratch the surface.

Real onyx can be scratched by anything with a Mohs hardness of 7 or above, so keep that in mind. Diamonds and other extremely hard stones fall into this category. If you have a collection of valuable stones, one advice is to keep the harder stones away from the onyx so that it doesn’t get scratched.

Read The Chemical Formula

If you’re shopping for a precious stone online, you might want to include its chemical composition in the item description. Onyx is made of silicon dioxide, so displaying the chemical formula for the material can be instructive. Remember that all silicate minerals include some combination of silicon and oxygen. Therefore the chemical formulas of different silicate minerals may be the same or extremely close to that of quartz.

Check The Price

The cost can also serve as a reliable indicator of genuine onyx. What did you pay for your onyx? Other factors, such as whether or not the onyx is set in gold and the size of the specimen, will alter the price.

Similar to gold, onyx is measured in carats to determine its worth. As of 2021, one carat of natural black onyx was worth approximately $40. The going rate per carat for synthetic onyx was about $6. However, very few examples of poor-quality carats might sell for as little as $5 per carat. Larger, better-quality carat specimens may sell for more than $600 in the U.S. per carat.

You may get a solid idea of the market value of your product by researching the prices of others like it. It is important to locate credible resources and sellers with solid reputations and credentials.

How To Take Care Of Black Onyx?

Keep your onyx jewelry in a box or pouch when it’s not being worn or shown. The Mohs hardness scale places a premium on maintaining separation from harder materials. Keep your artwork clean and away from any potentially damaging agents. This way will keep it looking beautiful for many years to come.


Genuine Black Onyx has a hardness of 7 on the Mohs Scale, making it indestructible even by a knife, and its surface is smooth, reflective, and clean without scratches or fissures. Knowing the essential information about this gemstone is vital when buying a stone to keep or a piece of jewelry to wear, making sure you are investing in genuine black onyx.

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