Tourmaline

EOSC 220 – November 23, 2004

Trigonal – Ditrigonal Pyramidal

Hardness (Mohs)

7 to 7.5

Specific Gravity 3.06 (+ 0.20; - 0.06)

Crystal System Hexagonal-trigonal

Colors Any and all. Tourmaline occurs in more colors than any other gem. Some colors have specific variety names, including:

• Bi-color: More than one color in the same stone • Chrome: Intense green, colored by chromium and/or

vanadium • Indicolite: Blue • Paraíba: Electric blue to green, colored by copper • Rubellite: Red • Watermelon: Pink in the center, green at the edge

Pleochroism Strongly dichroic with the ordinary ray having a darker color

Dispersion 0.017

Phenomena Cat's eye tourmalines are common. Color-change chrome tourmalines, which change from green to red, are occasionally found.

Tourmaline Group

Tourmaline Groups

Table 1. Current tourmaline end member species accepted by IMA

Species(X) (Y3) (Z6) T6O18 (BO3)3 V3 W

Alkali tourmaline

ElbaiteNa Li1.5 Al1.5 Al6 Si6O18 (BO3)3 (OH)3 (OH)

Schorl Na Fe2+3 Al6 Si6O18 (BO3)3 (OH)3 (OH)

Dravite Na Mg3 Al6 Si6O18 (BO3)3 (OH)3 (OH)

Olenite* Na Al3 Al6 Si6O18 (BO3)3 (O)3 (OH)

Chromdravite

Na Mg3 Cr6 Si6O18 (BO3)3 (OH)3 (OH)

Buergerite

Na Fe3+3 Al6 Si6O18 (BO3)3 (O)3 F

Povondraite*

Na Fe3+3 Fe3+

4Mg2 Si6O18 (BO3)3 (OH)3 O

Vanadiumdravite

Na Mg3 V6 Si6O18 (BO3)3 (OH)3 (OH)

Calcic tourmaline

Liddicoatite*

Ca Li2Al Al6 Si6O18 (BO3)3 (OH)3 F

Uvite* Ca Mg3 MgAl5 Si6O18 (BO3)3 (OH)3 F

Hydroxy-feruvite*

Ca Fe2+3 MgAl5 Si6O18 (BO3)3 (OH)3 (OH)

X-site vacant tourmaline

Rossmanite

LiAl2 Al6 Si6O18 (BO3)3 (OH)3 (OH)

Foitite* Fe2+2Al Al6 Si6O18 (BO3)3 (OH)3 (OH)

Magnesiofoitite

Mg2Al Al6 Si6O18 (BO3)3 (OH)3 (OH)

* These end-members are modified from the original suggested formulae to produce proper end-members (Hawthorne and Henry, 1999).

Buergerite

• NaFe+3Al6(BO3)3Si6O21F

• in cavities in a rhyolite • Bronze, Dark brown, Black • From near Mexquitic, San

Luis Potosi, Mexico

Chromdravite

• NaMg3(Cr,Fe+3)6(BO3)3

Si6O18(OH)4

• Greenish black, Dark green

• Onega trough, Karelia Republic, Northern Region, Russia

Dravite

• NaMg3Al6(BO3)3Si6O18(OH)4

• Metasomatically altered magnesian or dolomitic limestones in contact-metamorphic aureoles

• Black, Green, Red, Blue, White

• Drava River, Austria

Feruvite

• (Ca,Na)(Fe,Mg,Ti)3(Al,Mg,Fe)6

(BO3)3Si6O18(OH)4

• Brownish black, Dark brown, Black

• Repanga Island (Cuvier Island), Waikato, North Island, New Zealand

Foitite

• Na<0.5(Fe+2,Al)3Al6Si6O1

8(BO3)3(OH)4

• Bluish black • California

Liddicoatite

• Ca(Li,Al)3Al6(BO3)3Si6O18(O,OH,F)4

• Blue, Brown, Green, Pink, Red

• Detrital in soil, product of pegmatites

• From Antsirabe, Tsilaizina, and Anjanabonoina, Madagascar

Olenite

• NaAl3Al6(BO3)3(Si6O18)(O,OH)4

• Light pink • Aluminum-rich

tourmaline. Forms a series with elbaite

• Decembrist pegmatite field, Olenik River Basin, Russia

Povondraite

• (Na,K)(Fe+3,Fe+2)3(Fe,Mg,Al)6

(BO3)3Si6O18(OH)4

• Black • Alto Chapare district,

Chapare Province, Cochabamba, Bolivia

Schorl

• NaFe+3Al6(BO3)3Si6O18(OH)4

• Black, Brownish black, Greenish black, Bluish black

• Granites, diorites, gabbro pegmatites, greisens, skarns and quartz veins

• Sonnenberg, Bodenmais and Spessart, Germany

Uvite

• (Ca,Na)(Mg,Fe+2)3Al5Mg(BO

3)3Si6O18(OH,F)4

• Yellowish brown, Brown, Blackish brown, Bluish black

• Pegmatitic and skarn rocks

• Province Uva, Sri Lanka

Vanadiumdravite

• NaMg3V6(Si6O18)(BO3)3(OH)4

• Dark green, Black • Accessory mineral in

metamorphic rocks with quartz and Cr-V bearing diopside

• Slyudyanka complex, Lake Baikal region, Zabaikalye (Transbaikal), Siberia, Russia

Elbaite

• Na(Li,Al)3Al6(BO3)3Si6O18(OH)4

• Blue, Colorless, Green, Yellow, White

• Granitic pegmatites characterized by hydrothermal replacement

• Island of Elba, Italy

Elbaite

Elbaite

Watermelon Tourmaline

Cat’s Eye Tourmaline

Tourmalinated Quartz

Canadian - Stargazer

Canadian – Leduc, Quebec