Franckeite

Franckeite, chemical formula Pb5Sn3Sb2S14, belongs to a family of complex sulfide minerals. Franckeite is a sulfosalt. It is closely related to cylindrite.

Franckeite
Franckeite var. Potosíite, San José Mine, Cercado Province Bolivia. Field of view about 10mm.
General
CategorySulfosalt mineral
Formula
(repeating unit)		(Pb,Sn2+)6Fe2+Sn2Sb2S14
Strunz classification2.HF.25b
Dana classification03.01.04.02
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Identification
ColorGrayish black
Crystal habitTypically in spherical, rosette aggregates of thin plates; commonly massive, radiated, or foliated
TwinningComplex
Cleavage{010}, perfect
TenacityFlexible, inelastic; slightly malleable
Mohs scale hardness2.5 - 3
LusterMetallic
StreakGrayish black
DiaphaneityOpaque
Specific gravity5.88 – 5.92
PleochroismWeak
References[1][2][3]

It was first described in 1893 for an occurrence in Chocaya, Potosí Department, Bolivia. It is named after the mining engineers, Carl and Ernest Francke.[2] It can be found in Bolivia at Poopó in Oruro and at Las Aminas, southeast of Chocaya, in Potosi. Franckeite has an average density of 5.7 and can be both grayish black, blackish gray in color.

It occurs in hydrothermal silver-tin deposits in Bolivia and in contact metamorphosed limestone deposit in the Kalkar quarry in California. It occurs with cylindrite, teallite, plagionite, zinkenite, cassiterite, wurtzite, pyrrhotite, marcasite, arsenopyrite, galena, pyrite, sphalerite, siderite and stannite.[1]

See also

References
  1. http://rruff.geo.arizona.edu/doclib/hom/franckeite.pdf Handbook of Mineralogy
  2. http://www.mindat.org/min-1592.html Mindat with location data
  3. http://webmineral.com/data/Franckeite.shtml Webmineral data
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