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Buergerite

Buergerite
Category	Cyclosilicate mineral
Chemical formula	NaFe³⁺₃Al₆(BO₃)₃Si₆O₁₈(O,F,OH)₄
Identification
Color	Bronze, dark brown, black
Crystal system	Trigonal - ditrigonal pyramidal (3m)
Cleavage	Distinct prismatic
Mohs Scale hardness	7
Refractive index	nω = 1.735 nε = 1.655
Optical Properties	Uniaxial (-)
Birefringence	δ = 0.080
Streak	yellowish brown
Specific gravity	3.31
Diaphaneity	Translucent

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]