Aluminum, Calcium, & Calcium / Aluminum
Al2O3, CaO, and CaO/Al2O3 vs. Fe2O3(T)
Most meteorites have low concentrations
of aluminum (Al2O3) compared to terrestrial
rocks. The exception is meteorites from the Moon because
most lunar meteorites contain a high abundance of plagioclase
feldspar. For an explanation of why lunar meteorites plot
along the diagonal trend, see How
Do We Know That It's a Rock From the Moon? Feldspars
are common in terrestrial rocks, too.
Lunar meteorites also have high concentrations
of calcium (CaO) compared to most terrestrial rocks (except,
of course, those rocks rich in calcite, like the limestones
that plot around 50% CaO). The terrestrial rocks that plot
with the martian meteorites are probably basalts, which
have similar mineralogy to the martian basalts (but, see
Na2O & K2O).
In most meteorites, virtually all
the Al2O3 and most of the CaO is carried
by feldspar, so there is little variation in CaO/Al2O3.
Terrestrial rocks tend to have lower CaO/Al2O3
See Notes, Caveats, and References
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