#9 Your favorite...

DDW January Challenge #9, My favorite crystal rock

When I was in my 20s and 30s, I collected all sorts of crystals, gems, and stones. Here is one I've kept all these years. It has a place of honor in the living room since it is my favorite. I used to know the name of every one I had, but I've forgotten many of them. Does anyone know what this one is?