As a gemstone for jewelry moissanite is far superior, a much more brilliant stone. Here's some comparisons:
refractive indexes:
pyrope garnet - 1.74
diamond - 2.418
moissanite - 2.654 - 2.967
ruby - 1.76 - 1.77
cubic zirconia - 2.15-2.18
hardnesses:
diamond - 10
moissanite - 9.5
pyrope garnet - 7 - 7.5
ruby - 9
cubic zirconia - 8-8.5
Honestly with an 8.5 hardness and 2.18 refractive index I'm completely baffled why anyone would even want a ruby or garnet over a cubic zirconia. It's superior in every respect except in value because they're dirt cheap. It's foolish people covet things because they're expensive rather than their actual properties.
The most ridiculous thing of all is that diamond prices are artificially inflated because one single company controls their prices by keeping the supply artificially low, only allowing a fractional percent of the actual stock to be circulated.
More than that, read this article:
http://www.huffingtonpost.com/rohin-dhar/diamonds-are-bullshit_b_3708562.htmlAs soon as you leave the jeweler with a diamond, it loses over 50 percent of its value.
Americans exchange diamond rings as part of the engagement process, because in 1938 De Beers decided that they would like us to. Prior to a stunningly successful marketing campaign 1938, Americans occasionally exchanged engagement rings, but wasn't a pervasive occurrence. Not only is the demand for diamonds a marketing invention, but diamonds aren't actually that rare. Only by carefully restricting the supply has De Beers kept the price of a diamond high.
It's the equivalent of some company, let's give them some random name like Alumina, restricting the supply of aluminum so instead of it actually being available and dirty cheap it's instead sold in jewelry for more expensive than platinum. It's absolutely absurd.
What's more, diamonds can be grown in labs which are flawless -- and are real diamonds by the way... they're just called "synthetic" diamonds to make them less desirable even though they should be more desirable. They are superior in every respect and the saddest thing is that they sell for 20-30% less than normal diamonds. Oh and since they can be grown that means they can make diamond wafers which would catapults us into a new era of computing technology, replacing silicon with diamond.

And yet, we're held back by artificially high prices thanks to De Beers. It's criminal.
I mean for fucks sake, there are entire planets made entirely of diamond!