This is a lovely piece of Fluorite.  Quite a large specimen.  Please note that Fluorite is quite brittle, so take care of it.
 
Pure fluorite is actually white or colorless, but trace minerals give it many colors. Fluorite is transparent in most cases. The most commonly recognized fluorite color is a purple-blue mix but it is also found in blue, green, red and yellow colors.
 
Fluorite sits at a 4 on the Mohs Scale, which is very soft. The word “flourescent” is derived from flourite. Flourescence is the property of emitting light that has been absorbed previously–in essence, glowing. Generally minerals that are flourescent absorb ultra-violet light and then emit visible light, therefore the effect can only be seen by shining a UV light (black light) on them.