- © 2008 American Mineralogist
We live in interesting times. It used to be that mantle phase transitions were so few in number that even a child could become an expert—but my childhood is long past. Now even seismologists invoke obscure phase transitions to elicit favorable publishing decisions whenever an unexpected wiggle arises in a seismogram, and even mineral physicists routinely discuss seismic anisotropy. (Note to self: good reason not to drop optical mineralogy from a syllabus.) This surprising broadening of knowledge arose from the singular alliance of large-scale facilities provided by synchrotron light sources, supercomputers, and seismological data facilities like IRIS. Kei Hirose, John Brodholt, Thorne Lay, and David Yuen marshal the forces of this effort in their collection of papers, Post-perovskite, The Last Mantle Phase Transition, which highlights the knowns and unknowns of the Pbnm to Cmcm transition in MgSiO3 perovskite (pv) to post-perovskite (ppv). One known is that the seismic features in D″ are largely attributable to it. Oh, D″? That’s the bottom of the Earth’s mantle, a place where Birch’s famous warning applies: “Language undergoes a transformation to high pressure forms.” Now reread the prepenultimate sentence.
Possible hype notwithstanding, the editors provide a nice disciplinary packaging of the papers: experimental and theoretical mineral physics, seismology, and dynamics. The experimental section begins with two histories of high-pressure experimentation, a more general one by Yagi on mantle phase transitions, and a more ppv-centric one by Hirose. Their thrill of discovery is evident. While reading, I kept wondering what Ringwood would say. “You mean, you didn’t investigate analogues first?” was my surmise (but I imagine less politely put).
Graff Jewelers (Bond Street, London) report that wealthy Russian shoppers prefer yellow diamonds (source: International Herald Tribune). This is good …