Basics of mana

Vessels are rare in the world of Kaldashia. The dead vessels are perfect gems and soulstones, these are limited to how much power they can store. The alternative vessels are hearts of arcane beings such as dragons and demons these grow over the lifespan of the creature and hold untold potential. Extremely skilled artificers and mages even hold the hearts in living stasis and allow the vessels to grow over time even after they have been extracted.