Mackinawite

Mackinawite is an iron nickel sulfide mineral with formula (Fe,Ni)1 + xS (where x = 0 to 0.11). It crystallizes in the tetragonal crystal system and occurs as opaque bronze to grey-white tabular crystals and anhedral masses. It has a Mohs hardness of 2.5 and a specific gravity of 4.17.It occurs in serpentinized peridotites as a hydrothermal alteration product. It also is found in the reducing environment of fine grained river sediments, possibly produced by the action of magnetotactic and sulfate-reducing bacteria. It has also been reprted from meteorite occurrences.It was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.
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General Information:
 Chemical Formula:
(Fe,Ni)9S8
 Composition:
(Molecular Weight = 765.55 gm)
Iron 49.24 % Fe
Nickel 17.25 % Ni
Sulfur 33.51 % S 
 Empirical Formula:
Fe2+6.75Ni2.25S8
 IMA Status:
Approved IMA 1964
Physical Properties:
 Cleavage:
[001] Perfect
 Color:
bronze or white gray.
 Density:
4.3
 Diaphaniety:
Opaque
 Hardness:
2.5 - Finger Nail
 Luster:
Metallic
 Streak:
black
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