Zi Crystals are a unique hybrid organic that grows as a crystalline structure, they are attuned to and focus both Zi (magic-energy) and Chi (life-energy).
Zi Crystals are so far only found on the planet Anki and therefore the Anki Ascendancy has a monopoly on their sell and distribution (and therefore use to a degree).
Zi Crystals re-grow over time as well, but very slowly (like real crystals), over the centuries of their mining and harvesting, the Anki Ascendancy has learned tricks to make the crystals grow faster.
Zi Crystals are luminescent with a slight blue glow.
Scientists and Wizards have tried to create artificial Zi Crystals, but to no great success (they hold weak charges, shatter when depleted and cannot recharge).