Published: 5 August, 2004

Is it real or is it moissanite?

How can you tell if a diamond is real or fake?

The most common types of "fake diamonds" are made out of glass or of materials called cubic zirconia or moissanite. One of the properties that can be used to distinguish diamonds from other materials is its hardness. Real diamonds are the hardest naturally occurring materials, having a hardness of 10 on the Moh's scale which is a relative scale of hardness in minerals. So a real diamond will scratch anything else, including other natural gems such as ruby and sapphire or artificial gems such as the cubic zirconia or moissanite. Fake diamonds that are glass can easily be scratched by a steel file or a piece of quartz or other gems like ruby. The cubic zirconia has a hardness of 8.5 and can be scratched by a ruby or sapphire or a real diamond. The moissanite has a hardness of 9.25 and can only be scratched by a real diamond. However, jewelry that contains moissanite or cubic zirconia is still expensive and beautiful; you may not want to scratch it with a diamond to test whether or not it is real!

There are often other distinguishing features of diamonds such as small inclusions of other minerals. The inclusions usually cannot be seen without using a microscope or a hand lens (jeweler's loupe), but these inclusions are a way of determining that a diamond is real. Artificial gems will not have inclusions of other minerals. However, the very highest quality real diamonds will not have any inclusions in them.

Finally, the composition of "fake" diamonds is very different from that of real diamonds. Diamonds are composed of pure carbon. Cubic zicronia is made of zirconium oxide usually with some yttrium oxide. Moissanite is made from silicon and carbon. There are non-destructive ways to analyze materials to determine their composition. Many of these analytical techniques are available in the Cornell Center for Materials Research Shared Experimental Facilities. These analytical tools, which include electron microscopes and x-ray diffractometers, can quickly determine if a material is cubic zirconia, or moissanite, or real diamond.

Dr. Weathers has co-authored several scientific articles on the melting of diamond at high pressures.