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Franckeite var. Potosíite, San José Mine, Cercado Province Bolivia. Field of view about 10mm.
Category Sulfosalt mineral
(repeating unit)
Strunz classification 2.HF.25b
Dana classification
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Color Grayish black
Crystal habit Typically in spherical, rosette aggregates of thin plates; commonly massive, radiated, or foliated
Twinning Complex
Cleavage {010}, perfect
Tenacity Flexible, inelastic; slightly malleable
Mohs scale hardness 2.5 - 3
Luster Metallic
Streak Grayish black
Diaphaneity Opaque
Specific gravity 5.88 – 5.92
Pleochroism Weak
References [1][2][3]

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

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[edit]