Moissanite is a completely different gemstone than diamond. So the two actually have nothing to do with each other. Moissanite, however, looks very much like diamond. Because of this, the two gemstones are often compared. After all, only a connoisseur can tell the difference.
Moissanite is double refractive. Diamond, on the other hand, is singularly refractive. This means that moissanite reflects light twice, where diamond does so once. In addition, moissanite has a higher refractive index (2.65 versus 2.42). This means that moissanite reflects more "fire" (color) than diamond.
Also, diamond is the hardest gemstone in the world. Moissanite, however, comes in second. For example, diamond is a 10 on the Mohs scale (the highest score) and moissanite 9.25-9.5. Moissanite is therefore harder than sapphire, emerald and topaz! Only a diamond or other moissanite can scratch it. Like diamond, it is incredibly hard and virtually unbreakable.
Both diamond and moissanite can be found in nature. Moissanite, however, is much rarer. Commercially available moissanite, however, has always been grown in laboratories because it is far too rare in nature.
In addition, moissanite is overwhelmingly the ethical choice compared to diamonds, because moissanite has always been grown in laboratories while more than half of all excavated diamonds come from conflict zones.
Most people like the overall light reflection of moissanite better than diamond. Therefore, it does not make sense these days to spend so much money on diamonds, when you can get something more beautiful and of equal quality for a fraction of the price!
For more information, you can read this article.