What is "mackinawite"

n. (context mineralogy English) A tetragonal iron nickel sulfide mineral that occurs as opaque bronze to grey-white tabular crystals and anhedral masses.

Mackinawite is an iron nickel sulfide mineral with formula (Fe,Ni)S (where x = 0 to 0.11). The mineral crystallizes in the tetragonal crystal system and has been described as a distorted, close packed, cubic array of S atoms with some of the gaps filled with Fe. Mackinawite 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 was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.