The Gemstone Trophy was released on July 15th, 2010, as a reward for the limited edition Gemstone Collection. The collection is available from July 15th, 2010 to August 27th, 2010. After that, this Trophy is no longer available.
The trophy is in fact, a lot smaller than you would expect, a 1x1 size.
If you decide to buy this trophy instead of doing the collection, without having any collectable, it would cost you 53 cash.