Orientation of Exsolved Pentlandite in Natural and Synthetic Nickeliferous
AmericanMineralogist, Volume61, pages913-920, 1976 Orientationof exsolvedpentlandite in naturaland synthetic nickeliferous pyrrhotite Cenr A. FRANCISI,MtcHesl E. FLestz, KuL,q MlsnA.8,AND JenrEs R. Cnntcl rDepartment of Geological Sciences, Virginia Polytechnic Institute and State Uniuersity, Blacksburg, Virginia 24061 2Department of Geology, The Uniuersity of Western Ontario, London, Ontario N6A3K7 sDepartment of Geological Sciences, The Uniuersity of Tennessee,Knoxuille, Tennessee37916 Abstract Pentlandite(pn), (Fe, Ni)rSB,exsolves from nickeliferouspyrrhotite (po), (Fe, Ni)r-,S, in the form of flamesexhibiting weak reflectionanisotropism and preferredorientation. X-ray precessionstudies on both natural and syntheticcrystals have establishedthe orientation relation:(111)pnll (00.1)po; (0Tl )pn ll (l 1.0)po;(TT2)pn ll (10.0)po.In synthesisexperiments, rapidlyquenched samples of (Fe,Ni)r-,Ssolid solutions contain randomly oriented blebs of pentlandite,whereas slowly cooled charges contain coherent lamellae of pentlanditeparallel to (00.1)of pyrrhotite. Introduction typical Sudbury-typeFe-Ni sulfideassemblages lie within the monosulfidesolid-solution field at higher Threetextural varieties of pentlandite,(Fe,Ni)156, temperatures(Naldrett and Kullerud, 1967;Craig are common in the pyrrhotite-bearing(Sudbury- and Kullerud, 1969) further supportsthis inter- type) naturalnickel sulfide assemblages: (l) massive pretation.Thus the subsolidusexsolution origin of (blocky) pentlandite,often containingislands of pentlanditein nickel-sulfideassemblages
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