Mean particle size of Fe, MgSiO₃, and Al₂O₃ after 10³ yr exposed to a range of temperatures. Nucleation is so inefficient at large temperatures that metre-sized particles grow by vapour deposition on the very rare nuclei, but these particles do not absorb most of the vapour mass, as some vapour will not have time to undergo deposition. Lowering the temperature leads to a sharp decline in the particle sizes (and the fraction of vapour deposited on the grains increases abruptly from 0 to 100% below the transition temperature).