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The Tourmaline Group has a general formula of AX3Y6(BO3)3 Si6O18(O, OH, F)4.

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.

Tourmalines are abundant, complex boron and aluminum silicate minerals of variable composition. Tourmaline comes in a wide range of colors, depending on its mineral composition. Black is the most common.  

Colors can vary from clear, to pink, rosy-red, yellow, honey, green, blue, violet, brown and black . Some crystals are pink at one end and green at the other. Concentric color zoning often occurs as well. The colored varieties, when transparent and flawless, are cut as gems