Krystonia Krystals/Krystonia Crystals
Krystonia/Panton used "Swarovski Crystal Fireball" numbers 4861 (original figures) & 4869 (newer figures) on the Krystonia figures. They came in varying sizes and colors.
First Gen Krystonia used very colorful krystals as seen here in an early Rueggan:
And this "super rainbow" krystal as seen on the first N'Borg Staff (the pics don't do it justice):
Some pieces had no color at all - this Haapf's krystal is clear:
Later on, the "weak rainbow" krystals were the norm:
Replacement Krystals/Replacement Crystals
These crystals have been discontinued, but you can still find them via google if you want to repair them. They just used super-glue to adhere them to the figures originally, so if you have a piece missing a crystal, this should allow you fix it right up!
For the most part, they used the "weak rainbow" colored crystals except at the very early stage. Some pieces used diamond-shaped crystals (See Kephren's Chest, Gorph, Gorphylia etc).
Some links you can find replacement crystals/krystals: