Franckeite

Potosiite on Franckeite Locality: San Jose mine, Oruro City, Cercado Province, Oruro Department, Bolivia Specimen Size: 9.5 x 8.0 x 3.2 cm (cabinet) © Mineral Classics
Chemical Formula: Fe2+(Pb,Sn2+)6Sn24+Sb2S14
Locality: Found in Bolivia at Poopo in Oruro and at Las Aminas, southeast of Chocaya, in Potosi.
Name Origin: Named after the mining engineers, Carl and Ernest Francke.
Franckeite, chemical formula Fe2+(Pb,Sn2+)6Sn24+Sb2S14, 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. 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.

Physical Properties

Cleavage: {001} Perfect
Color: Grayish black, Blackish gray.
Density: 5.5 – 5.9, Average = 5.7
Diaphaneity: Opaque
Fracture: Flexible – Flexible fragments.
Hardness: 2.5 – Finger Nail
Luster: Metallic
Streak: grayish black

Photos :

Potosiite on Franckeite Locality: San Jose mine, Oruro City, Cercado Province, Oruro Department, Bolivia Specimen Size: 8.6 x 5.7 x 3.7 cm (small cabinet) Largest Potosiite crystal: 1.2 cm. © Mineral Classics
Franckeite Locality: San Jose mine, Oruro City, Oruro Dept., Bolivia Specimen Size: 3.0 x 2.5 x 2.0 cm (thumbnail) © Mineral Classics
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