Mooihoekite

Mooihoekite is a copper iron sulfide mineral with chemical formula of Cu9Fe9S16. The mineral was discovered in 1972 and received its name from its discovery area, the Mooihoek mine in Transvaal, South Africa.[4]

Mooihoekite
General
CategorySulfide mineral
Formula
(repeating unit)		Cu9Fe9S16
Strunz classification2.CB.10b
Crystal systemTetragonal
Crystal classScalenohedral (42m)
H-M symbol: (4 2m)
Space groupP42m
Unit cella = 10.58 Å, c = 5.38 Å;
Volume = 602.22 Å3; Z = 1
Identification
Formula mass1,587.59 g/mol
ColorPale yellow. Tarnishes to pinkish brown and purple
Crystal habitGranular - Generally occurs as anhedral to subhedral crystals in matrix
Mohs scale hardness4
LusterMetallic
StreakBlack
DiaphaneityOpaque
Specific gravity4.36
Optical propertiesWeakly anisotropic
References[1][2][3][4][5][6]

Crystal structure and optical properties

Mooihoekite crystallizes in the tetragonal crystal system. It has a short optical c-axis that is perpendicular to two longer a-axes of equal length. For Mooihoekite, the c-axis is a 4-fold rotoinversion axis.[2]

Mooihoekite is an opaque mineral which shows weak anisotropism in polished section under reflected light microscopy. It goes slightly extinct every 90°.[2]

Occurrence

It is found in massive sulfide from pipe-shaped dunite pegmatite in the norite zone of the Bushveld igneous complex in South Africa. It has also been found in troctolite from the basal Duluth gabbro in Minnesota, US; in the Talnakh area, Norilsk region, western Siberia; at Krzemianka, Poland; in the Malanjkhand copper-molybdenum deposit, Madhya Pradesh, India; and the Stillwater igneous complex in Montana, US.[5][6]

Mooihoekite occurs in association with haycockite, magnetite, troilite, cuprian pentlandite, mackinawite, sphalerite, and moncheite in the Mooihoek mine and with haycockite, native copper, troilite, pentlandite, cubanite and magnetite in the Duluth complex.[6]

Uses

Mooihoekite is a rare mineral that is mostly used for research purposes. It has similar properties to chalcopyrite CuFeS2, making it helpful in the study of ore deposits and the study of the central portion of the Cu-Fe-S phase system.[2] Mooihoekite, chalcopyrite, talnakhite, and haycockite all play key roles in the study of ore genesis and beneficiation.

References
  1. Mineralienatlas
  2. Cabri, L.J. and Hall, S.R. (1972) Mooihoekite and Haycockite, Two New Copper-Iron Sulfides, and Their Relationship to Chalcopyrite and Talnakhite. American Mineralogist, 57, 689-708.
  3. Hall, S.R. and Rowland, J.F. (1973) The Crystal Structure of Synthetic Mooihoekite. Acta Crystallographica, 29, 2365-2372.
  4. Webmineral data
  5. Mindat.org
  6. Handbook of Mineralogy
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