This is the 100th episode of the show by production order.
This is the first Appearence of Bismuth.
Bismuth is the first Gem on the show who is not technically a "gem". Bismuth is a metalloid substance which can in some cases crystallize into beautiful rainbowed patterns, like Bismuth's gem, but bismuth can also be found as an uninteresting metalloid in nature. However, technically, bismuth is known to have a "crystalline" molecular structure, which does make it a "crystal" in that regard.
This special is a full 30 minutes.
This is a special 100th episode of the show according to the airing order.