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Mackinawite

Mackinawite
Category	Mineral
Chemical formula	(Fe,Ni)₉S₈
Identification
Molecular Weight	85.42 gm
Color	Bronze to white Grey
Crystal habit	Anhedral grains to microscopic crystals
Crystal system	Tetragonal
Cleavage	Prefect on the [001]
Mohs Scale hardness	2.5
Luster	Metallic
Streak	Black
Density	4.17 g/cm³
Diaphaneity	Opaque

Mackinawite is an iron nickel sulfide mineral with formula (Fe,Ni)_{1 + x}S (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.

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