- Chemistry: (Pb, Sn)6FeSn2Sb2S14,
lead Tin Iron Antimony Sulfide.
- Class: Sulfides
- Subclass: Sulfosalts
- Uses: A very minor ore of lead and tin and as a mineral specimen.
Franckeite is a rare sulfide mineral. It is found in the sulfide ores
in Bolivia and Peru usually with other rare sulfides such as cylindrite,
Franckeite is a sulfosalt. Normally semi-metal ions such as antimony will
substitute for the sulfur atoms, but in the sulfosalts they substitute
for the metal ions and bond with the sulfurs.
The formula of franceite points out the difference between the two different
tin ions in the mineral. If the formula was written with the oxidation
states, it would look like this:
As can be seen there are two different tin ions. One is in a positive
two (+2) oxidation state and the other is in a positive four (+4) oxidation
state. The oxidation states also show the positive charge on the antimonies,
a condition found in sulfosalts.
Color is gray-black to gray-white.
Luster is metallic.
Transparency crystals are opaque.
Crystal System is triclinic; bar 1
Crystal Habits include accicular sprays and crusts.
Hardness is 2.5 - 3
Specific Gravity is approximately 5.8 - 6.0 (above average for
Streak is gray-black.
Associated Minerals include quartz,
as well as rare sulfides such as cylindrite,
Notable Occurrences are limited to Las Animas District, Bolivia
and Hulcani Mine, Peru.
Best Field Indicators are crystal habit, locality, color and