From:The Salt mines of Kłodawa, Poland
About Blue Halite: What do you see? Blue, blue blue! That is the question that people ask when they are looking at blue halite. To some, blue halite appears to be blue while others say it is colorless—but what's the true answer? The true answer lies in how lattice disorder interacts with light. If you bend and reflect light off of this crystalline structure (blue halite), you will create an illusion of blue color because Poland creates a lattice disorder within the crystal which causes reflections.