Hello PIGs: Essay #9 in the Study of Pegmatites series is now posted. It pertains to the article entitled: Jahns, R.H. and Burnham, C.W. (1969) Experimental Studies of Pegmatite Genesis: I. A Model for the Derivation and Crystallization of Granitic Pegmatites. Economic Geology and the Bulletin of the Society of Economic Geologists, 64, 843-864. The article is familiar to all who have pursued an academic interest in pegmatites. Familiarity is one thing, but as the saying goes, the devil’s in the details. The essay considers the model as presented by these authors and their experimental evidence for it. The evidence for and application of experimental results becomes the crucial point of the evaluation. After reviewing the main points of the Jahns-Burnham model, I have added some examples of my experiments that were meant to be simulations of the pegmatite-forming process. As I note in the essay, the challenges of interpreting such experimental results correctly are formidable, and conclusions are commonly more hypothetical than factual. I have requested permission to post the article to the PIG page. If that is granted, I will send a notification to PIGs via email. David London Learn about pegmatites and join the Pegmatite Interest Group at http://www.minsocam.org/msa/Special/Pig/