Distinguishing diamond from Moissanite

Last updated: September 8, 2023

MOISSANITE AND DIAMOND - TESTING MOISSANITE

Moissanite, its composition and manufacture (how synthetic Moissanite is synthesised).

How to tell diamond from Moissanite: diamond testers, Moissanite testers and multi testers.

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BASICS
MOISSANITE
MOISSANITE TESTERS
MOISSANITE TESTERS AND TYPE II DIAMONDS
NEW LOW-CONDUCTIVITY MOISSSANITE
MOISSANITE TESTERS AND UV (Ultra Violet light)
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BASICS

Moissanite is a manmade stone that looks like diamond. Its significance is that it tests as 'diamond' on standard diamond testers. Therefore, if you have a low-cost diamond-only tester, you will also need a Moissanite tester (though it's far simpler to get a 'Multi' tester that tests for both). The method is: test the stone on a diamond tester, if it reads diamond, it is either diamond or Moissanite - you won't know which. Then test the stone on a Moissanite tester to see if it is Moissanite. If it registers diamond on a diamond tester and not Moissanite on a Moissanite tester - then it's diamond.

Of course, it's far easier to get one machine that tests both, e.g. Multi-exp or SAM. tester.

MOISSANITE

Moissanite is a manmade stone (it doesn't exist in nature in a form that can be cut into gemstones*). It was 'invented' in the 1990s, its only significance is that it registers 'diamond' on standard diamond testers. Moissanite does, to the non-expert, look remarkably like diamond - but it is not diamond it is Moissanite, i.e. Moissanite is not a 'type' of diamond, it is another stone altogether.

* It's found either as tiny black crystals of Silicon Carbide (which can be synthesised to form the abrasive 'Carborundum') or as tiny platelets. You can see pictures of these 'platelet' cryststals here, but they are green, less than 1mm in size and cannot be cut into gemstones. Part of the publicity about Moissanite is true: that the French chemist Henri Moissan (hence "Moissanite") discovered the mineral in a meteorite crater in Arizona in 1893. But the gemstone stems from a 1998 patent for "translucent silicon carbide of a single polytype that are grown in a furnace sublimation system" - i.e. it is grown in a furnace in a laboratory.

MOISSANITE TESTERS

Moissanite registers as 'diamond' on diamond testers. That is why you need an additional tester (a Moissanite tester) to detect Moissanite.

Moissanite is electrically conductive (very slightly...you couldn't measure it on an ordinary electric meter) - and this is what a Moissanite tester detects.

Many other objects are electrically conductive (including your fingers!); many other gemstones are electrically conductive. However, diamond (with one very rare exception) is not electrically conductive.

Therefore:

- test the stone on a diamond tester
- if the tester reads 'diamond', it is either diamond or Moissanite.
- then test the stone on a Moissanite tester, if the tester reads 'Moissanite' then the stone is not diamond (though there is one very rare exception).

If you already have a diamond tester, buy a Moissanite tester.

If you don't have a diamond tester, your best-buy would be a multi-tester which is a combined diamond tester / Moissanite tester.

If you really wanted to save money, you could buy the very cheapest diamond tester and a Moissanite tester...though, personally, I wouldn't go for 'the cheapest' - they are never as reliable as the better models.

MOISSANITE TESTERS AND TYPE II DIAMONDS

Moissanite testers work by measuring electrical conductivity through the stone*. Most diamond is not electrically conductive, most Moissanite is. However, there is a very rare type of diamond (Type II diamond) which has an unusual atomic structure (it contains boron instead of the nitrogen) and this makes the diamond electrically conductive, i.e. it will register 'Moissanite' on a diamond tester.

Unless you are a diamond dealer handling diamonds every day, it's unlikely that you will ever see one of these. But, rare as these diamonds are, they are turning up at gem laboratories, sent in by anxious retailers following complaints by their customers who discover that their diamond registers 'Moissanite' on a Moissanite tester.

Incidentally, TYPE II diamonds are 'rare' by an accident of nature, due to their atomic structure, they are not 'rare' in the sense of being more valuable than 'ordinary' diamonds, they are exactly the same. In fact, logic dictates that it would be more difficult to sell a diamond that registers 'Moissanite' on a tester!

* The electrical resistance is measured all the way from from the stone, through the metal plates on the tester to your hand, then all the way round your body, back to your hand, and back into the tester - so it is essential to hold the tester with your finger on the metal plate of the tester.

NEW LOW-CONDUCTIVITY MOISSSANITE

Generally, Moissanite is electrically conductive (see above) but only very very slightly; generally, diamonds are not.

But there is an exception.

They are now making Moissanites which have very low electrical conductivity and register "Diamond" on most testers, including this Moissanite tester.

Therefore, the result on a Moissanite tester has a high probability of being correct but is no longer guaranteed.

The most reliable tester (out of the many we have tested) that detects most 'low conductivity' Moissanite is the SAM. Even with the SAM, we have managed to find a Moissanite that sometimes reads Moissanite and sometimes reads diamond (on the same stone).

MOISSANITE TESTERS AND UV (Ultra Violet light)

Unlike diamond testing, UV light does make a difference when testing a Moissanite on a Moissanite or combination (multi) tester.

The discovery was made by a gemmologist who worked out that, according to the laws of quantum physics, UV light should make a difference to electrical conductivity. He then took a deep breath and set about finding out just which type of UV light was required. To his amazement he found that any UV light worked. Moissanite testers that don't work on some 'difficult' Moissanites work better when the stone is exposed to UV light.

If you are buying a Moissanite tester, buy a UV light too, they really are not expensive. If you are buying our combination (multi Experior) tester, there is a UV light built in to the tester, and ours is the only model that will enable you to shine the UV light on the stone whilst testing (other models give you the choice of testing the stone or using the UV light, but not both at the same time, which isn't really of any use).