Bulk composition
Bulk composition is the overall chemistry of a whole meteorite sample, rather than of its individual minerals.
A meteorite's bulk composition is the average chemistry of a sample, usually a crushed or dissolved piece large enough to represent the whole rock. It lists the amounts of major elements, such as iron, magnesium and silicon, and of trace elements present only in parts per million or less.
Bulk compositions are central to classification. Chondrite groups differ in their total iron content, in how much of that iron is metal rather than oxidised, and in their ratios of refractory and volatile elements. Iron meteorites are sorted into chemical groups by their bulk nickel, gallium, germanium and iridium contents.
To get a reliable bulk analysis, the sample must be big enough to average out coarse features such as chondrules, CAIs or metal grains, and free of terrestrial weathering. Scientists often compare bulk compositions with the CI chondrites, whose chemistry matches the Sun's for most non-gaseous elements, to show how far a meteorite has changed from the original solar mix.
Related terms
Level: Enthusiast Teens and adults