chondritic unfractionated reservoir

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chondritic unfractionated reservoir (CHUR) Undifferentiated material from which chondrites are believed to have formed and in which elemental abundances are essentially the same as those in the solar atmosphere (see METEORITIC ABUNDANCE OF ELEMENTS; and SOLAR ABUNDANCE OF ELEMENTS). CHUR therefore provides a starting point for discussion of the chemical (and in particular the isotopic) evolution of the solar system.