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Essays #10 and #11 are now posted to the PIG website. Previous essays #8 and #9 on articles by Dick Jahns have stressed the importance of experimental studies to the Jahns-Burnham model. What experiments were done, and by whom, remains questionable. Experimental studies are central to these next two essays, but there is no question that they were done and by whom.
Essay #10 reviews three articles by Sam Swanson and Phil Fenn. These were the first significant investigations of the crystallization response of granitic and feldspathic melts to cooling. As fundamental as that process might seem, theirs were the only studies of note at the time and for years after. As I say in the essay, the real surprise is that their papers did not start a flurry of similar investigations. Fenn's experimentally based model for the origin of graphic granite remains as one of the most significant contributions to the study of pegmatites.
Essay #11, on a publication by David B. Stewart, reviews early experimental investigations of the stability of lithium minerals at geological conditions. In that work, Stewart identified the composition and mineralogy of the last zonal assemblage that could reasonably be attributed to crystallization from a silicate melt. Stewart used his article as a platform to present his preferred model for the petrogenesis of lithium-rich pegmatites, which if nothing else illustrates the breadth of views on the genesis of pegmatites. My own interactions with Dave Stewart are recounted in the context of the lithium aluminosilicate phase diagram.
All of the principal articles of these essays have been made available by the Mineralogical Society of America and by the Mineralogical Association of Canada. They are posted along with the essays in PDF.
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