Trace and minor elements in clinopyroxenes, amphiboles and basanitic melts produced in experiments at 0.5 to 2.0 GPa and 1000 to 1050°C were analysed by LAM-ICP-MS. The analyses reproduce the results of previous electron microprobe analyses by Adam & Green (1994) but also provide data for many new elements. The expanded data set was used to evaluate the trace element partitioning models of Blundy & Wood (1994) and Wood & Blundy (1997). Although the lattice-strain model of Blundy & Wood (1994) could be successfully fitted to our data, the thermodynamic model of Wood & Blundy (1997) does not predict the negative correlations that we found between DREE and pressure. This is not explained by variations in the amounts of H₂O in our experiments. Instead, we attribute the variations in DREE to volume-reducing substitutions in octahedral and tetrahedral sites that increase the activities of +3 and +4 ions, and decrease those of +1 ions, in sites of 8-fold coordination as pressure increases. We were able to quantitatively model some of these effects using a combination of simple electrostatics, Pauling bond strengths and bond-valence calculations. Notwithstanding this, it is apparent that pressure, temperature and the properties of the melt phase also influence partition coefficients independently of mineral composition and crystal-chemical effects.