[@Akayaofthemoon] Yeah, that's what I've been thinking as well.  I mean, I'm positive that there are less than 200 types of distinct gemstone, and the gems are heavily implied to be this huge, multi-planet spanning civilization that has fought in large-scale wars with heavy casualties.  It's hard to imagine that being possible if your entire species is well under 200 members strong.  Also, and this is fairly minor, Rebecca did a Reddit interview a while back and said [url=http://www.reddit.com/r/IAmA/comments/2e4gmx/i_am_rebecca_sugar_creator_of_steven_universe_and/cjw3wow] this. [/url]  I don't know, I think we have enough to go on to say that there probably is more than one type of each gem, but they probably haven't touched on this in the show because it would get confusing fast.

[@Loony] I've heard that too.  What exactly are people basing that theory on?  Sardonyx isn't all that yellow and is in no way a diamond.