Editorials

This past year has seen the departure of many of our great colleagues who shaped the fields of mineralogy, petrology, and geochemistry. They were part of our extended academic family and will be greatly missed. Although their academic contributions can be found in their curriculum vitae and scientific publications, their personal histories, the things that shaped their lives and careers, are more elusive. However, personal histories, where published, can capture the “human” aspect behind the scientist and include stories filled with happiness and humor, hardship and perseverance, and, above all, serendipity.

I would like to know, now that we’ve reached the year 2020, where is the hydrogen economy I was promised? Hydrogen fuel cell cars lurk at the margins of the marketplace, and several governments and corporations continue to make large bets on hydrogen’s future, but as I look out the window at my battery assisted, hybrid car, I’m still left wondering “what went wrong”?

The unique physical chemistry of carbon confers an extraordinary ability to form molecules that are variously beautiful (think diamond), essential (think living cells), and toxic (think greenhouse gas). Nowhere is this split personality more evident than in the enigmatic igneous clan of kimberlites, the topic for this issue of Elements. No one who has set eyes on a cut diamond, especially the delicate pink stones from soon-to-close Argyle Mine in Western Australia (see photo to the right), can fail to be awestruck at Nature’s capacity for beauty. Kimberlite magmas that bring diamonds to the surface are carbon-fuelled, whether by methane through a complex series of redox melting reactions (see Foley et al. 2019 this issue p. 393), or by carbon dioxide exsolving from kimberlite melt at sub-crustal depths and propelling it explosively to the surface (see Russell et al. 2019 this issue p. 405). We have yet to witness a kimberlite erupt – the last known eruption, in Tanzania, was ten thousand years ago – but we can be fairly sure that the greenhouse gas delivery of a single kimberlite pipe in full flow was pretty substantial. For kimberlites, carbon is both passenger and propellant.