Torshab Mine Stone

Abstract
Isocubanite is a cubic polymorph ofcubanite CuFezS3, discovered in the submarine sulphide deposits of
the East Pacific Rise (EPR) and the Red Sea, in association with chalcopyrite, pyrrhotine, pyrite, sphalerite
or wurtzite and anhydrite. It was previously obtained artificially and mentioned as iss, 'intermediate solid
solution of CuFe2S3 composition'. Crystals are cubic with a = 5.303(3)A and strongest lines in the X-ray
powder pattern are 3.059 (10) 111, 1.876(7)220,1.602 (5)311. Euhedral grains range from a fewmicrons up
to 400 }lm, with a Vickers microhardness of 175(25) kgjmm2 for P = 100 g. Isocubanite is usually
intimately intergrown with iron- and zinc-rich chalcopyrite and is opaque with a metallic lustre and a
bronze colour. Pinkish brown and isotropic in polished sections; reflectance values (SiC standard) are: 420
nm 22.73%,460 nm 26.87, 500 nm 31.34, 540 nm 34.79, 580 nm 37.35, 620 nm 39.11, 660 nm 40.32, 700 nm
41.33, 740 nm 41.91, 780 nm 42.50. Electron microprobe analyses gave (wt. %): Fe 41.64-42.49, Cu
20.79-21.52, Zn 0.77-1.09, S 35.49-35.82, corresponding to the formula (Cu,Zn)FeZS3.
Isocubanite ischaracteristic ofhigh-temperature (> 200°C) present-day submarine sulphide deposits
where hot hydrothermal fluids are quenched by seawater as in EPR deposits or by cooler brines as in
Atlantis II Deep, in the Red Sea; it is unstable and therefore unusual in fossil ores. This cubic phase was
previously observed and described more or less accurately as cubic cubanite, cubanite II, chalcopyrrhotite
and iss; the name isocubanite, proposed in order to clarify the nomenclature, and this new description,
were approved by the IMA Commission on New Minerals and Mineral Names.

Introduction
DURING a study of present-day submarine sul-
phide deposits, discovered in the East Pacific Rise
(EPR 21 ON)and the Red Sea (Atlantis II Deep), a
cubic polymorph of cubanite CuFeZS3 has been
observed in association with chalcopyrite, pyr-
rhotine, pyrite, sphalerite or wurtzite and anhydrite
(Noltner, 1979; Picot et al., 1980; Haymon and
Kastner, 1981; Styrt et a/., 1981; Oudin, 1981,
1983a; Pottorf and Barnes, 1983; Lafitte and
Maury, 1983; Koski et al., 1984; Zierenberg et al.,
1984; Oudin et al., 1984; Lafitte et al., 1984).
This polymorph can be obtained artificially by
heating orthorhombic cubanite between 200 and
270°C (Cabri et al., 1973;Fleet, 1970;Sawada et al.,

Mineralogical
Magazine, September
1988, Vol. 52, pp. 509 514
(Q Copyright the Mineralogical
Society
1962; Yund and Kullerud, 1961). It is frequently
mentioned in the literature as iss, 'intermediate
solid solution of CuFeZS3 composition' (Amcoff,
1981; Barton, 1973; Cabri, 1973; Kojima and
Sugaki, 1984; Sugaki et al., 1975).
It was apparently first reported by Ramdohr
(1928)and then by Odman (1933)under the name of
cubanite II. Later, Genkin et a/. (1965) almost
certainly recorded this phase in the ores of the
Noril'sk and Talnakh deposits, as fine rims on the
periphery of orthorhombic cubanite. The minerals
were not analysed, but X-ray data and reflectivities
show they are identical with the East Pacific Rise
and the Red Sea cubic polymorph of cubanite.
The name chalcopyrrhotit was first used by
Blomstrand (1870)for a material proved later to be





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