Moissanite (8.06)
Nobel prize winner Henri Moissan Ph.D discovered natural silicon carbide inside a meteorite in Diablo Canyon in 1893 even though in 1891 Edward Acheson first produced it in an attempt to create synthetic diamond. The substance was then named moissanite after Henri Moissan. After much research and development, moissanite (synthetic silicon carbide) was grown into large crystals for jewelry applications. Before that, synthetic silicon carbide was used for decades as an industrial abrasive (and still is). It does occur naturally but is considered very rare.
The Introduction to the Jewelry Market
In 1998 Charles & Colvard introduced the lab-grown moissanite to the jewelry market after obtaining the patents to create and sell them as an affordable alternative to diamond with a somewhat similar appearance.
Double Refraction
Diamond is singly refractive and moissanite is doubly refractive so this will be the most obvious characteristic when viewed. Since the moissanite crystal is consistently oriented in such a way to only show the doubling effect in a specific direction. This will be obvious in larger stones but can easily be overlooked in smaller. The culet must be viewed through the crown main (bezel) facet as you will see in the following images.
Hardness
Using the Mohs Hardness Scale, it is rated 9.25 to 9.5. This would make it harder than corundum, but much softer than diamond. Remember the hardness range between 9 and 10 far exceeds the difference in hardness between 1 and 9 on the scale. Hence moissanite is still a very hard substance, producing much sharper facet edges than for softer stones (and will remain so).
The above image is courtesy of: msblue.com
Differentiating Diamond and Moissanite by Weight
Diamond’s specific gravity is 3.52, whereas moissanite’s is 3.22. This indicates that moissanite is 91% of diamond’s weight, given the exact same proportions (or volume). So an easy way to identify or confirm the authenticity of moissanite would be to use the diamond weight estimation formula (discussed in greater detail in section 11).
For example, suppose the stone in question measures: 6.41 - 6.43 x 3.80 mm
Average diameter: 6.42 Depth: 3.80
Weight estimate formula would read:
6.42 x 6.42 x 3.80 x .0061=0.96 carat for a diamond.
Your carat scale shows a weight of 0.87 carat which would indicate moissanite since it is approximately 91% of the estimated diamond weight. At the very least you would be sure it is not diamond.
Color and Clarity
Clarity in moissanite varies from many needle-like inclusions arranged in directions parallel to the pavilion surfaces, to high clarity (clean). The needle-like inclusions in modern moissanite occur far less frequently than the older version.
The color of moissanite also varies, whereas the older generation were tinted with yellow, green or gray but due advancements in technology modern moissanites are generally clean and white.
Natural diamond-like inclusions never appear in moissanite, but of course, if the stone in question has a very high clarity, this alone would not be definitive.
Polishing Lines
Polishing lines, when present, will almost always run in the same direction on moissanite, since grain direction does not have to be taken into account in the faceting process. Remember that a diamond’s polishing lines will always run in multiple directions due to the fact that the cutter must always cut perpendicular to the closest influencing grain.
Facet Edges
Slightly rounded facet edges are another indicator of moissanite, but with better manufacturing methods and more skillful cutters, this may not be sufficient alone to confirm your identification.
The above photograph by Glenn Lovelady.
Testers
The older generation of diamond testers cannot be used to test moissanite. C3 was previously Charles & Colvard, (and other gem instrument manufacturers) sells a tester specifically for moissanite called the Model 590 Moissanite Tester in 1998. It is an electronic device similar to diamond testers. The author of this course does not recommend the use of testers, since they are not 100% reliable. As with any other electronic devices, a moissanite or diamond tester can become malfunction.
The above image is courtesy of: kassoy.com
With all the testing methods and your knowledge of diamond identification, moissanite should be straight forward, as long as you are thorough in your identification procedures.