Isocubanite

minerals

pyrrhotite

sphalerite

wurtzite

Formula: CuFe2S3
Sulphide, isometric paramorph of orthorhombic cubanite from which it can be formed by heating to between 200oC and 270oC (HOM); it is stable above 250oC (Dana).
Images
Specific gravity: 4.075 calculated
Hardness: 3½
Colour: Bronze, yellow, brown
Common impurities: Zn
Environments

Volcanic igneous environments
Hydrothermal environments

Isocubanite occurs as a primary sulphide precipitate from hot, saline solutions that cool under seawater (black smokers), in hydrothermal copper sulphide deposits, and in pumice from volcanic eruptions (HOM, Dana, Webmin). Associated minerals include chalcopyrite, pyrrhotite, pyrite, sphalerite, wurtzite and anhydrite (HOM).

Localities

The type locality is EPR 21° N, Juan de Fuca Ridge complex, East Pacific Rise, Pacific Ocean.

Alteration

Cubanite is very sensitive to temperature, pressure and compositional variations. In the laboratory cubanite has been transformed to isocubanite by increased pressure at ~4 GPa at room temperature. These results could be useful in estimating the metamorphic pressure conditions of cubanite-bearing carbonaceous chondrites (CM 48.1137-1147).

A sample of isocubanite from the Mid-Atlantic Ridge at 23oN transformed after a few months to a mixture of similar amounts of chalcopyrite and a phase of composition close to CuFe3S4 (AM 80.186).

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