There's a red crystal from Corellia, and a blue crystal that you get from the Gav Daragon museum.
They're not both essential, but having both is convenient
The red crystal from Corellia isnt necessary as long as someone has it to open the door (and someone is able to let anyone who falls and doesnt have it back in). The blue crystal is absolutely required. You cannot get the +10 datacrons without it. That said, it only takes about a minute to get it, and is in the same general location.