www.moissanite.com is a good starter spot. Moissanite is being
marketed as its own thing, not as a replacement for a diamond. It’s
fairly pricey, falling at about half the cost of diamonds I think.
It has a lot of interesting properties, is very hard and durable, and
has even more fire than diamonds.
I’m not sure how white they’re getting the stones though, or how
large a size in which they’re available.
The material is silicon carbide. Britannica is a good source of
background info: http://www.britannica.com/search?query=moissanite&ct=
I don’t know much about CZs.
Britannica has a bunch of info: