ABSTRACT The isotope mass fractionations of various refractory inclusions observed in the primitive materials as well as its estimated thermal origin are reviewed, which are generally inconsistent with the origins estimated by other procedures. The amount of mass fractionation cannot be a simple indicator to judge whether the inclusion was a condensate or an evaporation residue. Rayliegh mass fractionation occurs under a restricted condition. It is necessary to know the actual fractionation coefficient in the nebula, in order to discuss the relationship between the mass loss of a depleted element and its isotope fractionation in the primitive planetary bodies in terms of the Rayleigh distillation process. A step to realize two-dimensional isotope-ratio imaging is introduced for the purpose of compiling the isotopic data of various mineral phases having various condensation temperatures. The reconstruction of the thermal history over a wide temperature region may be possible from the compiled data.
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