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Tourmaline Chemistry

Tourmaline is a complex boron silicate mineral with a generalized chemical composition of:XY3Z6(T6O18)(BO3)3V3W

Letters in the formula above represent positions in the atomic structure of tourmaline that can be occupied by ions listed below.

 X = Ca, Na, K, [] ([] = vacancy)
 Y = Li, Mg, Fe+2, Fe+3, Mn+2, Al, Cr+3, V+3
 Z = Mg, Al, Fe+3, V+3, Cr+3
 T = Si, Al, B
 V = OH, O
 W = OH, F, O

The complex formula and many substituting ions produce the large number of minerals in the tourmaline group. The International Mineralogical Association has recognized 32 different tourmaline minerals based upon the chemical composition of solid solution series end members. These minerals are listed in the table below.

tourmaline crystals
Tourmaline crystals: Tourmaline crystals often have many fractures and inclusions, but these crystals exhibit wonderful clarity and very rich color. They also show the striations along the long axis of the crystals that are characteristic of tourmaline. The blue-green cluster on the left sits atop cleavelandite with purple lepidolite, and it measures 13 cm tall. The rubellite cluster on the right measures 6.7 cm tall.
Tourmaline Group Minerals
[] = vacancy
MineralComposition
AdachiiteCaFe3Al6(Si5AlO18)(BO3)3(OH)3OH
BosiiteNaFe3(Al4Mg2)Si6O18(BO3)3(OH)3O
Chromium-draviteNaMg3Cr6Si6O18(BO3)3(OH)3OH
Chromo-alumino-povondraiteNaCr3(Al4Mg2)Si6O18(BO3)3(OH)3O
DarrellhenryiteNaLiAl2Al6Si6O18(BO3)3(OH)3O
DraviteNaMg3Al6Si6O18(BO3)3(OH)3OH
ElbaiteNa2(Li3,Al3)Al12Si12O36(BO3)6(OH)6(OH)2
FeruviteCaFe3(MgAl5)Si6O18(BO3)3(OH)3OH
Fluor-buergeriteNaFe3Al6Si6O18(BO3)3O3F
Fluor-draviteNaMg3Al6Si6O18(BO3)3(OH)3F
Fluor-elbaiteNa2(Li3,Al3)Al12Si12O36(BO3)6(OH)6F2
Fluor-liddicoatiteCa(Li2Al)Al6Si6O18(BO3)3(OH)3F
Fluor-schorlNaFe3Al6Si6O18(BO3)3(OH)3F
Fluor-tsilaisiteNaMn3Al6Si6O18(BO3)3(OH)3F
Fluor-uviteCaMg3(Al5Mg)Si6O18(BO3)3(OH)3F
Foitite[](Fe2Al)Al6Si6O18(BO3)3(OH)3OH
LucchesiiteCa(Fe)3Al6Si6O18(BO3)3(OH)3O
Luinaite-(OH)(Na,[])(Fe,Mg)3Al6Si6O18(BO3)3(OH)3OH
Magnesio-foitite[](Mg2Al)Al6Si6O18(BO3)3(OH)3OH
MaruyamaiteK(MgAl2)(Al5Mg)Si6O18(BO3)3(OH)3O
OleniteNaAl3Al6Si6O18(BO3)3O3OH
Oxy-chromium-draviteNaCr3(Mg2Cr4)Si6O18(BO3)3(OH)3O
Oxy-draviteNa(Al2Mg)(Al5Mg)Si6O18(BO3)3(OH)3O
Oxy-schorlNa(Fe2Al)Al6Si6O18(BO3)3(OH)3O
Oxy-vanadium-draviteNaV3(V4Mg2)Si6O18(BO3)3(OH)3O
PovondraiteNaFe3(Fe4Mg2)Si6O18(BO3)3(OH)3O
Rossmanite[](LiAl2)Al6Si6O18(BO3)3(OH)3OH
SchorlNaFe3Al6Si6O18(BO3)3(OH)3OH
TsilaisiteNaMn3Al6Si6O18(BO3)3(OH)3OH
UviteCaMg3(Al5Mg)Si6O18(BO3)3(OH)3OH
Vanadio-oxy-chromium-draviteNaV3(Cr4Mg2)Si6O18(BO3)3(OH)3O
Vanadio-oxy-draviteNaV3(Al4Mg2)Si6O18(BO3)3(OH)3O

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