How Can You Tell If Black Onyx Is Real?

The popularity of black onyx fluctuates like a wave, depending on which celebrity is currently wearing it.

When it is popular, you’ll see companies and websites selling onyx jewelry or other onyx beads.

But since the value of onyx really varies, you won’t necessarily be able to tell if the onyx you are buying is the real stone or an imitation by the price tag.

In this article, we’ll show you how to tell if your block onyx is real.

How Can You Tell If Black Onyx Is Real? (Explained)

What Is Onyx?

To figure out whether your black onyx is real, it helps to understand what onyx is and what it should be.

Onyx can come in many colors, from black, to red, to just about every color you can imagine.

The term “onyx” is often used to describe materials that are black-colored (but do not contain onyx), as well as materials that hand parallel bands of black tourmaline, obsidian or opal.

Real onyx is an oxide mineral, with the formula SiO₂.

The reason we want you to know the chemical formula is so that you can connect the dots when we tell you that the formula of onyx matches the formula of quartz.

While people call onyx a form of chalcedony, they fail to make the connection that chalcedony has the same chemical makeup as quartz as well.

As you examine your black onyx, you should keep it in your mind that your onyx should exhibit characteristics that are similar to that of quartz.

Quick and Easy Tests To Tell If Your Black Onyx Is Real

Hardness Scratch Test

When you purchase black onyx, the seller may try to substitute plastic, resin, or another black mineral stone, like obsidian. These will generally not be as hard as onyx.

Quartz and onyx generally score in the range of 6-7 on the Moh’s scale of hardness.

As a result, materials that are less hard than onyx should not scratch or damage the surface of the stone in any way.

On the other hand, harder materials will scratch it.

Here are a list of items that you can test your material with:

fingernail
copper coin
standard kitchen knife

If your piece is pretty (but you just want to be sure), try and test an area of the material that is not obvious when you are wearing it, like the underside.

Another thing you can do is take the material and try scratching others with it, if you have then around.

Try scratching the onyx on softer stones, like selenite, fluorite, or apatite.

The onyx should be able to mar the surface of the other stones, without damaging the onyx itself.

Note: make sure that what you are scratching is the surface of the stone itself and not a finish or sealant.

If your stone is covered with an outer layer, you might just be damaging that outer layer and not actually reaching the stone.

Shape Review and Smash Test

Onyx beads are pretty common in the marketplace, and they are often sold as onyx when they are really just black plastic.

Look at the bead carefully.

Do you see anything on the bead that looks like it came out of a mold, such as a seam, or bubbling? If so, you’ve got plastic or some other material.

If you can’t tell if it is plastic, try putting the bead in a small plastic bag and smash it. Or try to.

Does the bead turn into teeny tiny pieces of dust on the first whack? If so, it’s probably not onyx.

If you hit the bead and it doesn’t disintegrate, but does break apart, look at the inside area. Is that area shiny, or dull?

The exterior of black onyx becomes shiny when it is polished.

The interior is obviously not polished. Thus if the inside looks shiny and polished, it is not onyx. It could be obsidian, or maybe even glass.

Heat Test

The melting point of quartz is more than 1000 degrees.

If you think your onyx might be plastic, a simple test would be to put the material over a heat source (such as a candle or lighter) and then see what happens.

If the onyx has changed shape in any way, it is not true onyx.

Acid Test

Some people recommend an acid test to confirm whether the material is truly onyx/quartz. Quartz is pretty non-reactive to many of the acids used in cleaning rocks.

Thus if you drop an onyx bead into muriatic acid or oxalic acid, we wouldn’t expect to see much in the way of fizzing or bubbling.

The reason that we dislike the acid test is that sometimes really pretty stones have microscopic cracks too small for us to see, or banding of other materials that would react with the acid but don’t hurt the look of the stone.

An acid test on a valuable or loved piece could destroy the piece, even if the “onyx” part of the piece is truly onyx.

Dyed Black Onyx

There is a lot of onyx out there in the world that has been dyed black.

In most cases, the black layer of the onyx stone may not be all that thick.

As a result, a lot of onyx is dyed to make the black uniform throughout the material, or to make the color itself more intense.

In fact, most onyx you find out in the world these days is dyed onyx.

Still onyx, but probably not as black.

The hard part about this is that dyed onyx is still onyx, meaning it still shares the same physical characteristics of quartz.

This the scratching, heating, and acid will not work to prove that your onyx piece was once a different color.

Given the advancements of technology, the only way to really prove if the onyx is truly black onyx through and through (and not some other color) is to get a look inside the stone.

This could be done by smashing a bead, by cutting the stone in half, or even by grinding away the exterior layers of the piece.

Parallel Bands

Most people don’t realize this, but onyx is generally differentiated from other minerals with similar chemical composition by parallel bands running through the material.

Small pieces of onyx could be crafted from a larger piece without the bands.

But a large piece of something called “onyx” should probably have some sort of parallel bands running through it.

If there are no bands, this piece might something else.

Wrap Up

This article comes from the practical point of view of a rockhound and lover of the outdoors.

While we aren’t jewelers, we expect that a professional could easily discern whether your black onyx is real pretty quickly, without having to scratch it or smash it.

When in doubt, take it to the professional before you destroy a valuable setting or stone.