Experimental petrology is a field of research concerned with experimentally determining the physical and chemical behaviour of rocks and their constituents.

Since the Earth’s mantle and core are not directly accessible, we have to infer their composition and structure by indirect means. This is achieved by combining data from seismology (the study of how seismic waves are modified by their passage through the Earth), with data from igneous rocks are meteorites. Since they are formed by melting rocks deeper within the Earth, the compositions of igneous rocks provide information about processes taking place during their formation and passage through the crust, and about the nature of their source regions. Meteorites provide direct samples of the interiors of other planetary bodies, whose internal processes are likely to have paralleled those on Earth. However, none of these approaches can provide much information alone.

Rocks are complex chemical systems, formed from upwards of ten major elements (plus a dozen or so trace elements), with complex multi-stage histories. One of the ultimate goals of the geologist is to use the composition and internal structure of rocks to understand the processes which gave rise to their formation – such as partial melting, mineral crystallization and trace element partitioning. For example, the presence of particular mineral phases with a rock constrains the P-T conditions at which it crystallized, since any phase is only stable under a very specific set of conditions. In addition, the concentration of trace elements within phases and glasses contains information about previously present phases and melting source regions. However, In order to make arguments like those above we need to know in advance the chemical behaviour of the elements and compounds from which real rocks are made. These are discovered experimentally in a lab, where the competing effects of other variables can be removed so that the behavour of specific features of the rocks can be investigated.

This is what we do in the experimental petrology group: we accumulate data on the physical and chemical behaviour of particular elements and compounds, so that this data can then be applied to more complex natural systems. We do this by literally making our own rocks (so that we can be sure what they are made of) and then imposing very specific conditions on them (carefully controlled temperatures, pressures and chemical environments) to see how they respond. In this manner, we can characterize the behaviour of natural rocks, and assist studies into planetary formation and differentiation.