Antitaenite

Antitaenite is a meteoritic metal alloy mineral composed of iron and nickel, 20-40% Ni (and traces of other elements) that has a face centered cubic crystal structure. Its existence as a new mineral species occurring in both iron meteorites and in chondrites was first recognized in 1995. [ D.G. Rancourt and R.B. Scorzelli. Low Spin γ-Fe-Ni (γLS) Proposed as a New Mineral in Fe-Ni-Bearing Meteorites: Epitaxial Intergrowth of γLS and Tetrataenite as Possible Equilibrium State at ~20-40 at % Ni. "Journal of Magnetism and Magnetic Materials" 150 (1995) 30-36] There are three other known Fe-Ni meterotic minerals: kamacite, taenite, and tetrataenite. The pair of minerals antitaenite and taenite constitute the first example in nature of two minerals that have the same crystal structure (face centered cubic) and can have the same chemical composition (same proportions of Fe and Ni) - they differ in their electronic structures: taenite is a high magnetic moment alloy whereas antitaenite is a low magnetic moment alloy. This unique difference in electronic structure was first established in 1999 [D.G. Rancourt, K. Lagarec, A. Densmore, R.A. Dunlap, J.I. Goldstein, R.J. Reisener, and R.B. Scorzelli. Experimental Proof of the Distinct Electronic Structure of a New Meteoritic Fe-Ni Alloy Phase. "Journal of Magnetism and Magnetic Materials" 191 (1999) L255-L260] and arises from a high-magnetic-moment to low-magnetic-moment transition occurring in the Fe-Ni bi-metallic alloy series. [ K. Lagarec, D.G. Rancourt, S.K. Bose, B. Sanyal, and R.A. Dunlap. Observation of a composition-controlled high-moment/low-moment transition in the face centered cubic Fe-Ni system: Invar effect is an expansion, not a contraction. "Journal of Magnetism and Magnetic Materials" 236 (2001) 107-130.] The same electronic structure transition is believed to be a causal factor in Invar behaviour.

References

* [http://www.mindat.org/min-6804.html Mindat with location data]
* [http://webmineral.com/data/Antitaenite.shtml Webmineral data]