Gems of the tourmaline family have the greatest range of colors of any gemstone and individual crystals may be color-zoned both from the inside out and from the bottom to top. This is a consequence of the chemical composition of minerals of the tourmaline group whose crystalline structures readily permit one metal ion to replace another. Names used for such crystals include, bi-colored tourmaline, parti-colored tourmaline, "party colored" tourmaline, and watermelon tourmaline.
Among the most attractive East African tourmalines are the greens colored by vanadium and chromium from Tanzania and Kenya and the electric blues and purples from Mozambique, colored by copper and manganese.
We also occasionally see red tourmaline colored by manganese, blues with iron as the coloring agent, canary-yellow titanium-bearing tourmalines, and other shades of green in which the color effect of a tiny amount of chromium has been naturally enhanced by the presence of magnesium. So far we have never seen an orange tourmaline, but who knows what the future may bring.

Chemistry:
System: Trigonal
Hardness: 7-7.5
Density: 3.06
Ref. Index: 1.624(+.005, -.005) - 1.644(+.006, -.006)
Birefringence:
Pleochroism: dichroic

On internet:
Green tourmaline on the ICA website
La tourmaline verte sur le site de l'ICA
View green tourmaline on mindat.org

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