While not actually a crystal, Lapis has long been prized as a spiritual stone.  Its usually dark blue or indigo in color.
It has been mined in Afghanistan for 6000 years. 
It is historically used to increase creativity, ESP, wisdom and self-acceptance.  It was believed to cure insomnia, depression and fevers.  The ancient Romans considered it an aphrodisiac.  It was one of the stone in the Breastplate of Aaron.  It was prised by the Egyptians and mentioned in several places in the Book of the Dead.  It is said to strengthen the throat chakra and heighten awareness when placed on the forehead chakra.  Not surprisingly, many psychics, mystical adepts, gurus, priests and ministers wear rings, crosses or pendants made of lapis.  I have a couple of them myself.
Here is an interesting crystal from my personal collection. I don't know what it is, but it has blue crystals almost the same shade as lapis, with some blue-green areas that are on the surface, not in the crystal.