  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 deficiencies of refractory siderophile
elements. I suggest that the planetary component of ordinary chondrite
formation consists of planet Mercury's missing complement of elements.
