Buergerite is a rare mineral from the ferric tourmaline group (class is silicates, sub-class is cyclosilicates) that was officially recorded in 1966. The tourmaline group includes the better known schorl, uvite and elbaite. Buergerite is found primarily near Mexquitic, San Luis Potosi, Mexico, in caves of igneous rock. To a lesser degree it has been reported in Brazil and the Central Bohemia Region of the Czech Republic.
The formula is NaFe3Al6(BO3)3Si6O18(O,F)4 Sodium Iron Aluminum Boro-silicate Oxide Fluoride. Unlike most tourmalines, analysis shows buergerite to be homogenous in composition. Its shape is described as trigonal-ditrigonal pyramidal. Its color ranges from bronze, to dark brown, to black with a yellow-brown streak. It is translucent to opaque. Crystals are short to long prismatic. It is pyroelectric and piezoelectric (has electrical polarity from temperature changes and stress). Its origin is probably pneumatolytic (formed by the vapors from magma).
It is easily confused with the mineral dravite, a similarly colored tourmaline, though dravite is found in metamorphic rock and buergerite is found in igneous. Its use is restricted to collector’s samples. The type samples can be found at the National Museum of Natural History (Smithsonian) in Washington, D.C., American Museum of Natural History, NY, and the Royal Ontario Museum, Toronto, Canada.
Buergerite is named for Martin J. Buerger (1903-1986), crystallographer and professor of Mineralogy at the Massachusetts Institute of Technology, Cambridge, MA. He pioneered the analysis of crystal structure and invented the equi-inclination Weissenberg X-ray camera followed by the X-ray precession camera which allowed photography of the diffractions of an individual crystal. He later went on to invent the X-ray powder camera. He is responsible for describing the complete structures of forty crystals, including tourmaline.
Dr. Buerger was the founder and first president of the Crystallographic Society of America in 1939 and an organizer of the American Society for X-ray and Electron Diffraction, both of which merged in 1950 to form the American Crystallographic Association (ACA). In 1958 he was part of the founding of the International Mineralogical Association.
In 1951 he was the recipient of the Arthur L. Day Medal by the Geological Society of America. He was presented with the Roebling Medal of the Mineralogical Society of America in 1958. Dr. Buerger authored a dozen books and over 250 articles in German and in English on Crystallography. The ACA established the MJ Buerger Award in his honor. In recognition of his accomplishment in America and internationally, and in fitting manner since he had long studied the tourmaline crystal, the newly discovered tourmaline was named buergerite for him when it was first discovered in 1965.
Sources
http://www.galleries.com/minerals/silicate/buergeri/buergeri.htm
http://webmineral.com/data/Buergerite.shtml
http://journals.iucr.org/j/issues/1986/04/00/a26354/a26354.pdf
http://www.minsocam.org/ammin/AM73/AM73_1483.pdf
