Kasha
From Wookieepedia, the Star Wars wiki.
The kasha was a crystal traditionally used by the Cereans as a meditation tool. They were used to clear the mind of distractions in order to create a perfect meditation environment. Patterns were scribed on each face of the crystal to harness its full energy potential, possibly created by Bi-Dar Tyunda thousands of years before.
When used as a lightsaber crystal, it helped clear the wielder's mind of distractions, even during tense combat.
It is unknown whether these crystals were usable by species other than Cereans, or if the crystals were specifically designed for their use.
