AFAIK, it\'s not just the structure but also the materials. Diamonds are made of carbon (they are simply highly compressed coal), whereas crystals are made of salts, the different minerals that make up the salts create basic properties like color, shape and hardness, while impurities usually change the basic color or create other effects like bands and such inside the crystal.
So for the complexity, we\'d need to find something that is made of crystals, like multicrystalline silicon or (!) the stalactite! Stalactite Blue? Or we would need to change to something not related to crystals but more complex, like organisms or something, or just organic blue. After that, it\'d be more macroscopic things, like planets and stuff like that, but one needs to be careful not to have it sound too much like classic SciFi. So maybe we\'d just move away from the complexity and towards something else.
