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Mackinawite

Iron nickel sulfide mineral

Field	Value
name	Mackinawite
category	Sulfide mineral
image	Mackinawite-95018.jpg
imagesize	260px
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
cleavage	Perfect on {001}
mohs	2.5
luster	Metallic
streak	Black
gravity	4.17
diaphaneity	Opaque
references

H-M symbol: (4/m 2/m 2/m) 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

Mackinawite occurs in serpentinized peridotites as a hydrothermal alteration product, in meteorites, and in association with chalcopyrite, cubanite, pentlandite, pyrrhotite, greigite, maucherite, and troilite. Mackinawite also occurs in reducing environments such as freshwater and marine sediments as a result of the metabolism of iron and sulfate-reducing bacteria.

In anoxic environments, mackinawite is formed by the reaction of HS− with either Fe2+ ions or with Fe metal.{{cite journal

Transformations in the environment

Depending on the redox conditions mackinawite can form more stable phases such as greigite and ultimately pyrite,{{cite book | editor-last1 = Amend | editor-first1 = J.P. | editor-last2 = Edwards | editor-first2 = K.J. | editor-last3 = Lyons | editor-first3 = T.W. | doi-access = free

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Mackinawite Mineralienatlas]
[http://rruff.geo.arizona.edu/doclib/hom/mackinawite.pdf Handbook of Mineralogy]
[http://webmineral.com/data/Mackinawite.shtml Webmineral data]
[http://www.mindat.org/min-2512.html Mindat]
{{cite OED2. mackinawite
(1970). "Structural refinement and composition of mackinawite". Carnegie Institute of Washington Geophysical Laboratory Annual Report.
Csákberényi-Malasics, D., Rodriguez-Blanco, J.D., Kovács Kis, V., Rečnik, A., Benning, L.G., and Pósfai, M. (2012) Structural properties and transformations of precipitated FeS. Chemical Geology, 294–295, 249–258. doi: 10.1016/j.chemgeo.2011.12.009.

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sulfide-minerals iron(ii)-minerals meteorite-minerals tetragonal-minerals minerals-in-space-group-129

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