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Mineralpedia Details for Franckeite

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Franckeite

Franckeite

Named to honor mining engineers Carl and Ernest Francke. Franckeite forms as hydrothermal silver-tin deposits in and in limestone in contact with metamorphic deposits. Localities for this uncommon mineral include in Bolivia, Argentina, the United States, Canada, France, Russia, China, Japan, and Australia, among only a couple others.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/franckeite.pdf

Formula
Fe2+(Pb,Sn2+)6Sn4+2Sb3+2S14 
Crystal System
Triclinic 
Crystal Habit
Tabular, Massive - Fibrous, Radial 
Cleavage
Perfect, None, None 
Luster
Metallic 
Color
grayish black, blackish gray 
Streak
grayish black 
Class
Triclinic - Pinacoidal 
Fracture
Flexible 
Hardness
2.5 
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Franckeite from Itos mine, near Oruro City, Oruro Dept., Bolivia

Franckeite
            from Itos mine, near Oruro City, Oruro Dept., Bolivia

Large spherical grouping to 2cm composed of thin platy single crystals to 3mm showing the typical bent forms and striations.

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Franckeite from San José mine, Oruro City, Oruro Dept., Bolivia

Franckeite
            from San José mine, Oruro City, Oruro Dept., Bolivia

This is an excellent specimen of this rare tin sulfide. The crystal aggregates occur as radial groups composed of what appears to be flat prismatic crystals. These groups are 1.3cm in diameter. In cross-section, however, these radial groups reveal themselves more as platy fan like groups. This is the other very peculiar and interesting member of the Cylindrite-Franckeite group.

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Franckeite from Mt. Bischoff mine, Waratah, Tasmania, Australia

Franckeite
            from Mt. Bischoff mine, Waratah, Tasmania, Australia

At one time this deposit hosted one of the world's richest tin mine. This specimen of Frackeite is rich in tin and hosted within Siderite. The Frankeite is typical with highly reflective metallic plates.

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