DIAMOND SIMULANTS

One gemstone can be used to imitate another more expensive vari­ety, for example citrine to imitate yellow sapphire, or colourless glass or quartz or American Diamond to imitate diamond. Colourless glass does not make a convincing diamond imitation as it lacks the hardness, fire and sparkle but no one dares to see the hardness of the diamond if it a glass.

Other diamond imitations include CZ (cubic zirconia) and, more recently, moissanite. Moissanite is almost as hard as diamond, mea­suring more than nine on the Mohs' scale. The main difference is that diamond is singly refractive, while moissanite is doubly refractive. In larger moissonite gemstones, this can be seen as a doubling of the pavilion facets when viewed through the stone, but in small stones mounted in jewellery, moissanite can be difficult to recognize and they are seldom identified.

There have been other diamond simulants, including for example yittrium aluminium garnet (YAG) and strontium titanate, but all have either lacked fire, or had too much been too soft or too brittle. Diamond simulants can be distinguished from diamond by the fact that they conduct heat far less readily than diamond. Touching the stone with a thermal conductivity meter will alert the gemologist to the imitation.