Board Thread:News and Announcements/@comment-7267707-20130320212114/@comment-3552584-20130322220054

The crystal you got was a Quartz Crystal, from the newly-included mod (as of 0.6.1), Applied Energistics. The crystal from Mystcraft looks like glowstone, only blue, and never found in the overworld. However, if an age has the symbol for it, crystal formations are quite commonly generated on the surface of that Age.