Mineralpedia Details for Franckeite

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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
WebMineral: View Franckeite
Mindat: View Franckeite

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

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

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.