mackinawite

{{Infobox mineral | name = Mackinawite | category = Sulfide mineral | image = Mackinawite-95018.jpg | imagesize = 260px | caption = | formula = (where x=0 to 0.11) | IMAsymbol = Mkw | molweight = 85.42 g/mol | strunz = 2.CC.25 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = P4/nmm | unit cell = a = 3.67 Å, c = 5.03 Å; Z = 2 | color = Bronze to white grey | habit = As well-formed thin tabular crystals; massive, fine-feathery | twinning = | cleavage = Perfect on {001} | fracture = | tenacity = | mohs = 2.5 | luster = Metallic | polish = | refractive = | opticalprop = | birefringence = | dispersion = | pleochroism = | fluorescence= | absorption = | streak = Black | gravity = 4.17 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque | other = | references = }} Mackinawite ( ) is an iron sulfide mineral, which can contain nickel substituting for iron(II), with as chemical formula (where x = 0 to 0.11). As indicated by its chemical composition, Fe(1+×), Fe is present with an excess of × over S, and it is thus an iron-rich, or a sulfur-deficient, iron monosulfide mineral. 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.

==Occurrence==