Bertrandite

Bertrandite

Bertrandite, the white part of this crystal, is named after mineralogist Emile Bertrand, who discovered it near Nantes, France in 1883.  It tends to replace other minerals, such as Beryl, atom-by-atom, in what is called a pseudomorph or false-form.  It is rarely found alone and often accompanies fluorite, as with this crystal.  Still, it is pretty rare.  When the deposit where the crystal forms moves, it cracks, and new minerals fill those cracks creating a stained glass appearance and therefore the name, Tiffany Stone.

Also known as Ice Cream Opal.