Chemical Composition of Meteorites
Silicon (Si) as Silica (SiO2)
SiO2 vs. Fe2O3(T)
Many terrestrial rocks have higher concentrations of SiO2 (silica) than any meteorite. Many of these contain quartz. If SiO2 is greater than 60%, the rock is not a meteorite. The only possible exception would be a lunar granite, which is a volumetrically insignificant component of the Apollo collection. The low-SiO2 chondrites are all carbonaceous chondrites. Carbonaceous chondrites have a substantial proportion of volatile elements that, in terms of this plot, as a diluants that drag the compositions toward the origin. The low-SiO2 terrestrial rocks are mainly limestones [low Fe2O3(T) + MgO] and iron ores [high Fe2O3(T) + MgO].