Chromite is a ubiquitous early crystallising phase in mafic and ultramafic magmas. It has long been used as a ‘petrogenetic indicator’ in igneous and metamorphic rocks, as its wide range of solid solutions reflect the composition of the magmas that chromite crystallised from. Unusually for a mafic mineral, chromite is robust both during metamorphism and sedimentary transport, and can retain primary information about its source rocks where no other primary mafic minerals are preserved. Chromite also strongly partitions platinum-group elements, including osmium, making it suitable for study using the Re-Pt-Os isotope systems.

In this presentation, I document my descent into chromite research, from a naïve interest in ultramafic lavas, through investigations into the age and origin of ultramafic bodies in Greenland, to the broad scale evolution of the Earth’s mantle and continental crust. I outline how the composition of chromite varies during crystallisation of mafic and ultramafic melts, and how chromite trace elements can help us narrow down the parental melt composition of intrusions. I discuss the use and abuse of the Re-Pt-Os systems to place ages on the formation of chromite and its host rocks. Finally, I introduce fuchsitic quartzites; rare, predominantly Archaean metasedimentary rocks that contain abundant detrital chromite. I present ongoing work to develop the use of detrital chromite grains as a tool to understand the growth of continental crust, and address the problem of Earth’s ‘missing’ mafic crustal record.