Oriented chlorite lamellae in chromite from the Pedra Branca Mafic-Ultramafic Complex , Ceari , Brazil

Chromite grains in chromitite from the Pedra Branca Mafic-Ultramafic Complex,Cear6, Brazll, contain lamellar inclusions of chlorite oriented parallel to {l I l}. The chromite grains have a core of aluminian chromite and a broad margin of ferrian chromite, formerly called "ferritchromit." The chlorite is a Cr-bearing IIb clinochlore, and the inclusions occur preferentially within "ferritchromit." The orientation relationship is c*.n".,.11[111].n--,., a.nb,i,.ll[rr0].h.o*,,", and b,n",ftlllhh'nl"n,"-,,". This is equivalent to the orientation ofchlorite-olivine intergrowths and corresponds to topotaxial sharing ofa layer of closest-packed anions at the interface between the two phases. Because of the considerable misfit in the strain-free equivalent lattices, the interface structures in both chloritechromite and chlorite-olivine intergrowths may consist of an interlayer sheet (brucite layer) of H bonded to a layer of closest-packed O of the host substrate. Chloritization of the chromite was broadly contemporaneous with the alteration to "ferritchromit."

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