Refractory element
A refractory element condenses into solid minerals at very high temperatures, such as calcium, aluminium and titanium.
A refractory element is one that forms solid compounds at high temperatures and so was among the first to condense from the hot gas around the young Sun. Calcium, aluminium, titanium, the rare earth elements, zirconium, iridium, osmium, tungsten and uranium are all refractory.
In meteorites, refractory elements are concentrated in calcium-aluminium-rich inclusions, which formed at the highest temperatures. Scientists compare the abundance of refractory elements in different meteorite groups with their abundance in CI chondrites, which closely match the Sun's own composition. CV chondrites, for example, are enriched in refractory elements partly because they contain many CAIs.
Refractory elements tend to stay put when rocks are heated or melted at moderate temperatures, so ratios between them often survive later processes. That makes them reliable tracers of the original building blocks of a planet. Iridium is a refractory, metal-loving element whose spike in clay layers led to the discovery of the dinosaur-killing impact.
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