Tourmaline is a gorgeous gemstone and available in a wide range of colors. It was discovered in Brazil, but for many years it was confused with other gems. It was not until the 1800's that it was identified as 'Tourmaline'. Aside from the famous mines of Brazil, Tourmaline can be found in several countries of Africa, Afghanistan, and California and Maine in the U.S.
There are several, complex mineral species that make up the Tourmaline group, but the base chemical formula is (Na,Ca)(Mg,Li,Al,Fe2+)3Al6(BO3)3Si6O18(OH)4. Other smaller amounts of trace elements present in the host (pegmatitic rock) will alterate the composition and produce the various species and colors.
Tourmaline is part of trigonal crystal system. It's unique columnar structure is formed by rings of silica tetrahedra. Elongated cuts are many times favored for this stone to accentuate the saturation of color along the axis , making some of the stones highly pleochloric. Color zoning is also seen in Tourmaline, producing beautiful bi-color and muti-color stones.
Tourmaline has a Refractive Index of 1.624 to 1.64
Specific gravity: 3.06 (+0.20, -0.06)
Mohs Hardness: 7 to 7.5