Synthetic moissanite has come onto the market. It is a man made stone that has properties that very, very closely resemble diamonds. It fools the thermal conductor tester for diamonds and will therefore give a false diamond reading. An inexperienced or inattentive jeweler or gemmologist could easily be fooled by moissanite.
I am concerned that you may buy what you think is a very high grade diamond from a jeweler that is in fact a round brilliant cut sample of moissanite. The jeweler may have been fooled as well. The 'IGS DIAMOND BUYER'S GUIDE explains step-by-step the exact procedure you should follow in order that you or your fiancee does not end up wearing a moissanite for years to come thinking that it is a high grade VS or VVS clarity diamond.
The purchase of the guide will ensure that you do not mistakenly buy moissanite for diamond. It's so similar to diamond that it's frightening.
The guide has a full detailed chapter on moissanite that will protect you from mistakenly purchasing one instead of a diamond by applying the knowledge set forth in the guide will make your diamond shopping experience a relaxing and pleasurable experience and you won't end up with moissanite. You can't afford not to know about moissanite before you go shopping for a diamond.