Beautiful Bicolour Tourmaline Crystal. Some would call this specimen a Water Melon Tourmaline.
3.2cm x 1cm x 1cm, 6.5g or 34ct.
Himalaya Mine, Pala, California, USA.
The Tourmaline Group has a general formula of AX3Y6(BO3)3 Si6O18(O, OH, F)4. The A can be either calcium or sodium. The X can be either aluminum, iron, lithium or magnesium. The Y is usually aluminum, but can also be chromium or iron. Some potassium can be in the A position, some manganese can be in the X position and some vanadium can be found in the Y position, but these elements are usually not represented in the formulas of the tourmaline members.