That's from Wikipedia. The only thing I know about Bismuth is that it isn't a gem, so I have no idea what this episode could be about.
Let's find out at 7:00 ET/PT on Cartoon Network. Clear your schedules, because this episode is double-length! If you don't have the time, we've got streams and downloads after the break.
The Brony Network
Cartoon Network's Official Stream
DHN Livestream [Closed Captioned]