How Can You Tell a Real Diamond from a Fake Diamond?

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It is an age-old scam: the conman produces a surprisingly good quality diamond and comes out with a sob story. The rube, thinking they are getting a great deal and helping a foolish fellow, hands over a goodly sum and receives the diamond – only to find that the good diamond has been switched for a fake. Or was a good fake right from the beginning… There are substitute stones that offer the right clarity, color, and cut to fool even a relatively wise purchaser – one who might consult an impartial guide on diamond clarity such as the one found here: But is there any foolproof way of telling a real diamond from a fake?

The short answer is, no. There are some tests that pinpoint certain features of a diamond, but these tests can be fooled by some fake diamonds. The best bet is to do several of the following tests and see if the stone passes all of them: which a real diamond would!

Up to Scratch?

The oldest known test for a diamond was to see if it would cut through glass or a mirror, and this still holds true: a real diamond will scrape a mark onto a glass surface. But so will moissanite and cubic zirconia, two of the best known ‘fake’ diamonds. Both elements occur naturally, with moissanite being quite rare in its own right, being a silicon carbide inclusion found within other minerals, while cubic zirconia is zirconium dioxide in a cubic crystalline form, again, fairly rare in nature. With both of these stones, synthetic manufacture has made them both fairly common and relatively cheap, with large crystals growing readily in lab conditions. Moissanite is a relatively new substitute for diamonds, only being produced for commercial aesthetic purposes in the late 1990s. So, if your diamond makes a mark on glass or mirror, you are most likely in possession of a diamond or moissanite or cubic zirconia.

Admiring the Sparkle

This is a fairly unscientific way to determine if you have a diamond, and a well-cut moissanite or cubic zirconia can fool even relative experts, but a diamond has a unique inner fire that reflects and refracts light in unusual and exciting ways, creating a sparkle that is very hard to beat. However, cubic zirconia and moissanite can both sparkle very enticingly, so it is more for jewelers who deal with diamonds on a daily basis who are more likely to spot the subtle differences in stones. One trick that does work well is to place the stone face down on a piece of text, or even a dot. If the text can be read, and the dot seen clearly, the stone is almost certainly not diamond. Diamond’s fabulous light reflectivity means that something seen through the diamond will be bounced around withing the facets so thoroughly as to become invisible or so muddled as to be illegible.

Good Conduct

Diamonds, being pure carbon, are good conductors of both heat and electricity. Loosely, this means diamonds will rapidly cool down upon being heated up, and will readily conduct an electrical current, completing rather than breaking an electrical circuit. Again, one of the substitute stones, moissanite, is a good thermal conductor, so once the thermal test is passed, the electrical conductivity test should be initiated before moissanite can be firmly ruled out.

A Weighty Affair

Diamonds are strong gemstones, but they are not especially heavy, with cubic zirconia being 1.7 times denser than diamonds. Thus, a cube of the diamond, 4mm across will weigh 1.7 times less than a similar stone of cubic zirconia. Moissanite, on the other hand, is lighter than diamond, by about seven percent – so the stone 4mm across will be about half the weight of cubic zirconia and noticeably lighter than the diamond. Once the weight of a certain size of a diamond is known, this can be used fairly accurately to tell if you have a diamond or a cunning replica. One supposed test for diamonds is to drop it into the water and see if it falls fast or wafts down more slowly – this will only serve to weed out a glass and very lightweight stones, as cubic zirconia will actually fall quicker than diamond, while moissanite will not be too far behind the genuine diamond.

As you can see, ascertaining whether one has a real diamond or not is more a case of elimination than an affirmation: only once all the tests have been completed can one say that it seems that one has a diamond – and now all you have to do is work out the value of that diamond using the four Cs! It is infinitely better to use a reputable jeweler who will provide a certificate of GIA accreditation with every stone sold for true peace of mind.

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