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Category Sulfide mineral
(repeating unit)
(Fe,Ni)1 + xS (where x = 0 to 0.11)
Strunz classification 02.CC.25
Crystal symmetry Tetragonal 4/m 2/m 2/m
Unit cell a = 3.67 Å, c = 5.03 Å; Z=2
Formula mass 85.42 g
Color Bronze to white grey
Crystal habit As well-formed thin tabular crystals; massive, fine-feathery
Crystal system Tetragonal - ditetragonal dipyramidal
Cleavage Perfect on {001}
Mohs scale hardness 2.5
Luster Metallic
Streak Black
Diaphaneity Opaque
Specific gravity 4.17
References [1][2][3]

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 reported from meteorite occurrences. It occurs in association with chalcopyrite, cubanite, pentlandite, pyrrhotite, greigite, maucherite and troilite.[1]

It was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.[3]

See also[edit]