The tourmaline group is a large group of cyclosilicates (ring silicates) that are borosilicates.

The generalised tourmaline structural formula is XY3Z6(T6O18)(BO3)3V3W

Tourmaline minerals can be assigned to groups depending on the dominant content of the X site, which may be

Tourmaline Groups

X site Group
Na1+ or K1+ alkali group
Ca2+ calcic group
Vacancy X-vacant group

Maruyamaite is the only known tourmaline mineral with K at the X site.
Each of the groups can be divided into sub-groups, determined by the dominant content of the Y site, which may be Al3+, Cr3+, Fe2+, Fe3+, Li1+, Mg2+, Mn2+, Mn3+, Ti4+ or V3+.

Other sites are occupied as follows:
Z: Al3+, Fe3+, Mg2+, Cr3+
T: Si4+, Al3+, B3+
B: B3+
V: OH1–, O2–
W: OH1–, F1–, O2–
If F1– or O2– are dominant at the W site, the prefix fluor- or oxy- respectively is appropriate, as in fluor-buergerite and oxy-chromium-dravite

(AM 96.895–913)

Colour Varieties of Tourmaline

An alternative way of identifying tourmaline minerals , which are often a mix of these different mineral species, is by their colour. Colour varieties include:

achroite, a colourless variety, usually, but not always, elbaite
blue cap tourmaline, a variety of elbaite with its top portion dark blue, and the rest of the crystal red or pink
indicolite, a blue gemmy variety, usually, but not always, elbaite or fluor-elbaite. Most blue tourmalines are coloured by ferrous iron (Fe2+) as well as iron to iron charge transfer (Fe2+ - Fe3+) (
rubellite, a red gemmy lithium-rich and more or less iron- and magnesium- free variety, primarily elbaite or fluor-elbaite, but may also be olenite or fluor-liddicoatite
verdelite, a green variety
watermelon tourmaline, a variety of concentrically colour-zoned tourmaline with red interiors and green exteriors

Properties of tourmaline
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid


Plutonic igneous environments
Pegmatites (common and characteristic)
Metamorphic environments
Hydrothermal environments

The most common and characteristic occurrence of tourmaline is in granite pegmatites with elevated boron content, and in the rocks immediately surrounding them. If there is sufficient boron and aluminium in the melt, schorl is the first tourmaline species to form, then elbaite. Tourmaline is found also as an accessory mineral in igneous rocks and metamorphic rocks.
Most pegmatitic tourmaline is black and associated with the common pegmatite minerals microcline, albite, quartz and muscovite.
Light lithium-bearing tourmaline also occurs in pegmatites, frequently associated with lepidolite, beryl, apatite and fluorite.
Hydrothermal tourmaline is found in sediment-hosted massive sulphide deposits, such as the Sullivan deposit in British Columbia, Canada, associated with chlorite, manganese garnet, pyrrhotite, quartz and muscovite variety sericite. Also intrusion-related, associated with albite, biotite, carbonates, muscovite and quartz (AofA).

Tourmaline may be found in granite, phyllite and limestone.


At the Golconda mine, Minas Gerais, Brazil, cookeite pseudomorphs after tourmaline have been found (KL p238).

At the Sapo mine, Minas Gerais, Brazil, fine tourmaline including elbaite, indicolite, "blue-cap" tourmaline and watermelon tourmaline is found in the pegmatite. Most of the crystals are loose, but some are resting on an albite or quartz matrix. Schorl is also abundant, associated with quartz, albite and microcline (Min Rec 40.4.290). Polylithionite pseudomorphs after tourmaline have also been found at Minas Gerais (KL p237).

At the Dafoe Property, Pierrepont, St Lawrence county, New York, USA, tourmaline crystals occur on walls and within open spaces in a tourmaline-bearing pegmatite vein. The black tourmaline crystals are complexly zoned with fluor-uvite cores and dravite rims (R&M 94.5.452-455). The tourmaline occurs as lustrous black individual crystals to 9 cm that can be found in clusters to 20 cm. Crystals are normally euhedral lacking striations, and they are often hemimorphic. Rarely, crystals form in a prismatic habit with their lengths sometimes being more than twice that of their width. Most crystals are moderately to highly fractured (R&M 97.3.250).

On the eastern slopes of Plumbago mountain, Newry, Oxford County, Maine, USA, in 1972 the largest single discovery of gem-quality tourmaline in North America was unearthed, more than a ton in all. It came from a pocket in the pegmatite 29 feet in length containing over 2,000 pounds of tourmaline crystals, the largest being a watermelon tourmaline weighing just over 4.7 kg (R&M 98.1.78-83)

List of tourmaline minerals

Mineral Formula Group Y-site
olenite NaAl3Al6(Si6O18(BO3)3O3(OH) alkali Al3+
darrellhenryite Na(Al2Li)Al6(Si6O18)(BO3)3(OH)3O alkali Al3+ and Li1+
elbaite Na(Al1.5Li1.5)Al6(Si6O18)(BO3)3(OH)3(OH) alkali Al3+ and Li1+
oxy-dravite Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O alkali Al3+ and Mg2+
oxy-chromium-dravite NaCr3(Cr4Mg2)(Si6O18)(BO3)3(OH)3O alkali Cr3+
fluor-schorl NaFe2+3Al6(Si6O18)(BO3)3(OH)3F alkali Fe2+
schorl NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH) alkali Fe2+
oxy-schorl Na(Fe2+2Al)Al6(Si6O18)(BO3)3(OH)3O alkali Fe2+ and Al3+
dutrowite Na(Fe2+2.5Ti0.5)Al6(Si6O18)(BO3)3(OH)3O alkali Fe2+ and Ti4+
fluor-buergerite NaFe3+3Al6(Si6O18)(BO3)3O3F alkali Fe3+
fluor-elbaite Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3F alkali Li1+ and Al3+
chromium-dravite NaMg3Cr6(Si6O18)(BO3)3(OH)3(OH) alkali Mg2+
dravite NaMg3Al6(Si6O18)(BO3)3(OH)3(OH) alkali Mg2+
fluor-dravite NaMg3Al6(Si6O18)(BO3)3(OH)3F alkali Mg2+
princivalleite Na(Mn2Al)Al6(Si6O18)(BO3)(OH)3O alkali Mn2+ and Al3+
maruyamaite K(MgAl2)(Al5Mg)(BO3)3(Si6O18)(OH)3O alkali Mg2+ and Al3+
feruvite CaFe2+3(Al5Mg)(Si6O18)(BO3)3(OH)3(OH) calcic Fe2+
fluor-liddicoatite Ca(Li2Al)Al6(Si6O18)(BO3)3(OH)3F calcic Li1+ and Al3+
fluor-uvite CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3F calcic Mg2+
uvite CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3(OH) calcic Mg2+
alumino-oxy-rossmanite ☐Al3Al6(Si5AlO18)(BO3)3(OH)3O X-vacant site Al3+
rossmanite ☐(Al2Li)Al6(Si6O18)(BO3)3(OH)3(OH) X-vacant site Al3+ and Li1+
foitite ☐(Fe2+2Al)Al6(Si6O18)(BO3)3(OH)3(OH) X-vacant site Fe2+ and Al3+
magnesio-foitite ☐(Mg2Al)Al6(Si6O18)(BO3)3(OH)3(OH) X-vacant site Mg2+ and Al3+
celleriite ☐(Mn2+2Al)Al6(Si6O18)(BO3)3(OH)3(OH) X-vacant site Mn2+ and Al3+

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