For hundreds of years, alternative materials, both natural and synthetic, have been used as diamond imitations. The main reason for this is the relative rarity of diamonds which results in their higher price compared to their imitation counterparts. Another reason is the controversy surrounding ethical mining practices and the existence of conflict diamonds. Also known as simulants, they resemble diamonds in appearance and may even have certain diamond-like properties, but a gemmologist or laboratory should be able to differentiate clearly between them.
Synthetic stones used as imitations include glass, cubic zirconium, synthetic rutile and synthetic moissanite, among others. Cubic zirconium remains the most common imitation. Introduced in 1976, it has a strong visual likeness to diamond, is relatively hard, has good dispersion, and its cost is low. However, it lacks the fire of a diamond, can scratch more easily, is often completely colourless, has a high density and won’t react to a thermal tester. Synthetic moissanite is another popular imitation. Introduced in 1998, it is closer to diamond in hardness and density. However, due to the way the stone disperses light, gemmologists can look for doubling of facets and inclusions, which gives a clue as to its true identity. Natural diamond simulants include quartz, topaz and zircon. Finally, there are also composite stones in which two or more parts are bound together by an adhesive.
In general, there are some clues gemologists and diamond graders can look for to decide whether what we have is a diamond or not. Diamonds are typically free from scratches and their highly lustrous facets have sharp edges. Diamonds may fluoresce (blue is the most common colour) whereas imitations usually display little response to shortwave ultraviolet light. Whereas diamonds are often slightly tinted and have telltale inclusions such as fractures and foreign crystals, simulants may well be completely colourless and are often free of inclusions.
One of the first tests that is usually done is using a thermal tester with a probe, which tells diamonds apart from other stones as they are highly effective thermal conductors. Although moissanite fooled these testers for many years, more recently, testers have been developed that do detect moissanite.
In practical terms, if you have a gemstone which is either loose or in a jewellery piece, and you’re unsure if it’s a diamond or an imitation, visit a reputable jeweller. In less than a minute, the thermal tester will give you an indication of the gemstone’s identity.