tourmaline

The Tourmaline Group

The tourmaline minerals constitute of group of borosilicate minerals that share a common structure, but that have a variety of possible cations that occupy sites in the crystal structure.

Tourmaline Classification Scheme
(as proposed by Hawthorne and Henry (1999))

Buergerite	NaFe³⁺₃Al₆(BO₃)₃Si₆O₁₈(O)₃(OH)
Chromdravite	NaMg₃Cr₆(BO₃)₃Si₆O₁₈(OH)₄
Dravite	NaMg₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
Elbaite	Na(Li_1.5Al_1.5)Al₆(BO₃)₃Si₆O₁₈(OH)₄
Foitite	[][Fe²⁺₂Al]Al₆(BO₃)₃Si₆O₁₈(OH)₄
Hydroxy-feruvite	CaFe²⁺₃[Al₅Mg](BO₃)₃Si₆O₁₈(OH)₄
Magnesiofoitite	[][Mg₂Al]Al₆(BO₃)₃Si₆O₁₈(OH)₄
Liddicoatite	Ca(Li₂Al)Al₆(BO₃)₃Si₆O₁₈(OH)₃F
Olenite	NaAl₃Al₆(BO₃)₃Si₆O₁₈(O)₃(OH)
Povondraite	NaFe³⁺₃[Fe³⁺₄Mg₂](BO₃)₃Si₆O₁₈(OH)₃O
Rossmanite	[](LiAl₂)Al₆(BO₃)₃Si₆O₁₈(OH)₄
Schorl	NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
Uvite	CaMg₃[Al₅Mg](BO₃)₃Si₆O₁₈(OH)₃F

[] in these formulas refers to a vacant cation site (the X site)

Buergerite, from Arangua, San Louis Potosi, Mexico.

Dravite from Australia colored by Fe²⁺-Ti⁴⁺ IVCT

Red dravite from Kenya with high concentrations of Fe³⁺

Pink Elbaite from Pala, California, naturally colored by radiation damage to Manganese.

Manganese(2+)-rich elbaite from Zambia

Schorl-Dravite in a thin section showing color zones due to variations in the total iron content and in the ratio of Fe²⁺ to Fe³⁺

Povandraite on matrix from Bolovia

Dr. Povandra from the Czech Republic

Professor Foit from Washington, USA

Magnesiofoitite from Kyonosawa area, Yamanashi-Ken Prefecture, Honshu, Japan. Maximum rod length is 0.2 mm

Magnesiofoitite is considered a rare mineral described only in 1998. Foitite, while seldom recognized as such, may be common. Many specimens of schorl may, in fact, be foitite. However, elaborate chemical analysis is necessary to distinguish these minerals.
Nine cm long fragment of a foitite crystal from Cahuilla Mountain, Riverside County, California, USA.

Liddicoatite from Madagascar

Richard Liddicoat from California, USA

Rossmanite in lepidolite from Rozná, Czech Republic

George Rossman from California, USA

Elbaite Gems.

Schorl in a pegmatite dike in Mysenec, Czech Republic

Deep red uvite from Brumado, Bahia, Brazil

Professor Foit from Washington, USA	Magnesiofoitite from Kyonosawa area, Yamanashi-Ken Prefecture, Honshu, Japan. Maximum rod length is 0.2 mm
Magnesiofoitite is considered a rare mineral described only in 1998. Foitite, while seldom recognized as such, may be common. Many specimens of schorl may, in fact, be foitite. However, elaborate chemical analysis is necessary to distinguish these minerals.	Nine cm long fragment of a foitite crystal from Cahuilla Mountain, Riverside County, California, USA.