Jamesonite

Jamesonite is a sulfosalt mineral, a lead, iron, antimony sulfide with formula Pb4FeSb6S14. With the addition of manganese it forms a series with benavidesite. It is a dark grey metallic mineral which forms acicular prismatic monoclinic crystals. It is soft with a Mohs hardness of 2.5 and has a specific gravity of 5.5 - 5.6. It is one of the few sulfide minerals to form fibrous or needle like crystals. It can also form large prismatic crystals similar to stibnite with which it can be associated. It is usually found in low to moderate temperature hydrothermal deposits.
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(n.)
A steel-gray mineral, of metallic luster, commonly fibrous massive. It is a sulphide of antimony and lead, with a little iron.
  

General Information:
 Chemical Formula:
Pb4FeSb6S14
 Composition:
(Molecular Weight = 2,064.07 gm)
Iron 2.71 % Fe
Antimony 35.39 % Sb
Lead 40.15 % Pb
Sulfur 21.75 % S 
 Empirical Formula:
Pb4Fe2+Sb6S14
 Name Origin:
Named after the Scottish Mineralogist, R. Jameson (1774-1854).
Physical Properties:
 Cleavage:
[001] Perfect
 Color:
lead gray, steel gray, or dark lead gray.
 Density:
5.5 - 5.63, Average = 5.56
 Diaphaniety:
Opaque
 Habits:
Acicular - Occurs as needle-like crystals., Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite), Massive - Fibrous - Distinctly fibrous fine-graine d forms.
 Hardness:
2.5 - Finger Nail
 Luminescence:
None.
 Luster:
Metallic
 Streak:
black. grayish
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