Black Diamond VS Onyx – 5 Key Differences & A Few Alternatives

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Black diamonds are perhaps some of the most intriguing diamonds possible. Normally when you think of a diamond you think of a clear one, sparkling and flashing a rainbow at you. Not black diamonds though. They subvert every expectation and still manage to impress. So what if you decide you like black diamonds, but you’re not entirely sure you want to commit to such a big investment ? Here’s where onyx comes in.

Onyx has often been used as a black diamond dupe in jewelry, so it makes sense to wonder just what the differences are between these two gems. Today we’re discussing black diamonds vs onyx, so you can decide which gem would be better for you.

black diamond vs onyx

Black diamond vs onyx

Black diamonds are far tougher than onyx, and they come in a wider range of intensity and clarity than onyx. Because of this black diamonds are also far, far more expensive than onyx, which just makes them that more intriguing. Overall onyx seems to be easier to get a hold of for most people than black diamonds.

What is black diamond ?

Black diamonds are a form of diamond with many, many graphite inclusions. Graphite is a form of carbon as well, but it appears as dark grey or nearly black with some serious metallic luster to it. So black diamonds are simply heavily included clear diamonds, to the point where they can’t even be mistaken for grey diamonds anymore.

What is onyx ?

Onyx is a form of chalcedony, which may present white or colorful bands. Most of the time onyx will be cut to reveal only the black parts. You can easily find onyx for sale, and although onyx comes in many colors most sellers will carry black onyx only.

1. Onyx is uniform black, black diamonds vary

When you’re looking at onyx vs black diamonds, you’re essentially comparing their color potential. Well, you must understand that onyx and black diamonds do this differently and sometimes they do look almost identical.

To understand this let’s first look at onyx. This is an opaque material, and if you were to cut into it you may or may not find bands of a different color hidden underneath the black. Most of the time though onyx jewelry will only show the pure black part of the gem. So an even color, completely opaque.

Read also: Ruby VS Red Diamond

Black diamonds are on a spectrum, ranging from completely clear (white diamonds) to completely included (carbonado diamonds). Grey diamonds are in the middle of this range. Anything between a grey diamond and a carbonado can be considered a black diamond. This means one person’s black diamond may still have some clarity to it, while another may have a 100% opaque black diamond.

This variety in clarity and color may mean that your black diamond of choice may sparkle just a little bit or not at all. Any black diamond you choose will be unable to sparkle like a white one, simply because it is so heavily included, please remember that.

2. Black diamonds are far tougher than onyx

Black diamonds are still diamonds, and as such they are far tougher than onyx. A black diamond scores a 10 out of 10 on the Mohs hardness scale, while onyx scores a 7 on the same scale. This makes Onyx a softer stone than black diamond, meaning it can scratch and chip if not handled with care.

So if you do decide to get onyx for your jewelry, you should:

  • restrict it to occasional wear, such as formal events or just nights out
  • take it off whenever you’re doing any sort of chore
  • get a pendant or earrings as these are hit and scratched far less than a ring or bracelet
  • be willing to replace or polish the gem every few years, if it’s a ring or bracelet

If you decide to get a black diamond you can, of course, wear it however you like because it will withstand absolutely anything you throw at it.

3. Onyx is far more affordable than a black diamond

Prices vary from gemstone to gemstone, and here we can take a look at the difference between onyx and black diamond. Onyx sell for an average of $5 per carat, which is very affordable.

Black diamonds are again, on a spectrum. Black diamonds that are not completely opaque, so those that could also be classed are very dark grey diamonds, usually sell for an average of $130,000 per carat. The lighter the color the higher the price, so very dark ones – nearly black but still fairly clear – will sell for a bit less than that.

Meanwhile the very dark ones that are so heavily included they appear opaque, or almost opaque, sell for an average of $4,000 per carat. So they are far more affordable than the other versions of black diamond, and these are also the one black onyx is used to substitute.

No matter what kind of black diamond you compare to onyx, onyx will always appear far more affordable by comparison.

4. Black diamonds are harder to find than onyx

Black diamonds may prove harder to track down than onyx when you actually start to look for one. This doesn’t mean you should not get black diamonds, we’re just trying to explain that you may need more patience than you initially thought.

Even if your jeweler can get you a black diamond, you have no guarantee it will be the clarity you want it to be. Remember, the darker the diamond the more included it is, so it really comes down to how flexible you are on what you want.

Onyx only comes in the one color: deep, inky black so there is no hemming and hawing with onyx. This is simpler but may prove to be a bit boring for some, so keep that in mind.

5. Onyx has less of a sheen than black diamond

Black diamonds have an adamantine sheen or luster to them, which is easier to see on the heavily included black ones. This means their sheen is a bit metallic-looking, and not just white as the light bounces off of it. The heavily included ones may present tiny spots which are actually places where the inclusions have reached the very surface of the diamond.

Onyx has a different sheen, or rather it doesn’t have much of a sheen. Onyx does reflect a spot of white light, but it mostly tends to absorb the light. Onyx appears so dark and inky it’s difficult to find the sheen on it.

Can you use onyx instead of black diamond ?

You can use onyx in place of a black diamond only if you’re trying to replace a heavily included black diamond. Those diamonds have zero clarity and because of this the onyx will look just like it. In time the onyx will scratch and chip, and this may create an interesting pattern, depending on your tastes.

If you intend to use onyx instead of a clearer black diamond, one with far less inclusions, then onyx is not the best choice. For these cases a better alternative is grey moissanite. These gems can come in any color you like, and you can find them in very dark grey/almost black just like you would find diamonds. The difference is that moissanite is not included, it simply is grown in that color.

If you want a more natural gemstone, you can try either rutilated or smoky quartz, but be warned these won’t offer the exact same effect.

Rutilated quartz has thousands of bands of rutile going through it, to the point where some specimens look like very included diamonds, of course, you’d need a very specific rutilated quartz: thin bands, thousands of them, all of the black or grey in color.

If you go for smoky quartz, you need to find one that is more on the grey/black side than the dark brown color. Smoky quartz has patches of darker and lighter color, as if someone trapped smoke within it.

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