Chemical Composition of Meteorites

MgO

Among meteorites, MgO necesarily increases with Fe₂O₃(T) + MgO. Some terrestrial rocks lie off the trend because they have MgO/Fe₂O₃(T) ratios outside the range for meteorites (below). High-MgO terrestrial rocks are mainly ultramafic rocks like dunites and serpentinites.
  

Fe₂O₃(T)

The same is largely true for Fe₂O₃(T). High-Fe₂O₃ terrestrial rocks are iron ores.
  

MgO / Fe₂O₃(T)

The ratio of magnesium to iron does not vary greatly among most kinds of stony meteorites.
Rocks with MgO/Fe₂O₃(T) <0.2 or >6 are not meteorites.

See Notes, Caveats, and References