Electron microprobe analysis of samples from the Pennsylvania-Maryland State Line District show that disseminated chromites associated with serpentinites commonly have a ferrit-chromit rind (<1 wt percent Al2O3; <3.5 wt percent MgO; >25 wt percent Cr2O3).This rind, which completely encloses the chromite core, has an irregular overgrowth of magnetite (>85 wt percent iron oxide) which is embayed by serpentinite silicates. The out-line of the original chromite grain may possibly be represented by either (1) the outer or (2)the inner edge of this rind.

The genetic association of chlorite with ferrit-chromit established by Beeson and Jackson(1969) for the Stillwater complex can not be extrapolated to this rock suite. In the State Line deposits, the lack of associated aluminous silicates and the low aluminum content of the ferrit-chromit rule out solid state diffusion for the formation of the ferrit-chromit. Aqueous mobilization of chromium during serpentinization is reviewed as a possible mechanism.

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