Fluor-buergerite

Fluor-buergerite,[4] originally named buergerite, is a mineral species belonging to the tourmaline group. It was first described for an occurrence in rhyolitic cavities near Mexquitic, San Luis Potosi, Mexico. It was approved as a mineral in 1966 by the IMA and named in honor of Martin J. Buerger (1903–1986), professor of mineralogy at the Massachusetts Institute of Technology. It has also been reported from Minas Gerais, Brazil, and the Central Bohemia Region of the Czech Republic.[1][2][3]

Fluor-buergerite
General
Category	Cyclosilicate tourmaline
Formula (repeating unit)	NaFe^3+3Al6(BO3)3Si6O18(O,F,OH)4
Strunz classification	9.CK.05
Crystal system	Trigonal
Crystal class	Ditrigonal pyramidal (3m) H-M symbol: (3m)
Space group	R3m
Identification
Color	Bronze, Dark Brown, Black, Dark Purple
Cleavage	Distinct prismatic
Mohs scale hardness	7
Streak	yellowish brown
Diaphaneity	Translucent
Specific gravity	3.31
Optical properties	Uniaxial (-)
Refractive index	nω = 1.735 nε = 1.655
Birefringence	δ = 0.080
Other characteristics	Pyroelectric and piezoelectric
References	[1][2][3]

References

1. Handbook of Mineralogy
2. Mindat
3. Webmineral data
4. Darrell J. Henry; Milan Novák; Frank C. Hawthorne; Andreas Ertl; Barbara L. Dutrow; Pavel Uher; Federico Pezzotta (2011). "Nomenclature of the tourmaline-supergroup minerals" (PDF). American Mineralogist. 96: 895–913. doi:10.2138/am.2011.3636.