  The high occurrence on Earth of ordinary chondrite meteorites and the making
of models based upon arbitrary assumptions has led to some confusion about the
origin of ordinary chondrites. Major element fractionation among chondrites has
been discussed for decades as ratios relative to Si or Mg. Expressing ratios
relative to Fe leads to a new relationship admitting the possibility that
ordinary chondrite meteorites are derived from two components: one is a
relatively undifferentiated, primitive component, oxidized like the CI or C1
chondrites; the other is a somewhat differentiated, planetary component, with
oxidation state like the reduced enstatite chondrites. Such a picture would
seem to explain for the ordinary chondrites, their major element compositions,
their intermediate states of oxidation, and their ubiquitous defiencies of
refractory siderophile elements. I suggest that the planetary component of
ordinary chondrite formation consists of planet Mercury's missing complement of
elements, presumably separated from protoplanetary Mercury during its
formation.
