Hello PIGs: Essay #12 is now posted on the PIG page. It pertains to this article: Chakoumakos, B.C. and Lumpkin, G.R. (1990) Pressure-temperature constraints on the crystallization of the Harding pegmatite, Taos County, New Mexico. Canadian Mineralogist, 28, 287-298. The key contribution of that study was an application of a conductive cooling model for the Harding pegmatite, New Mexico. Depending upon the boundary conditions chosen, the model predicted rapid cooling to subsolidus temperatures on the order of 3 to 100 years. Compared to previous notions that the giant sizes of crystals found in pegmatites require very slow cooling over many (millions) of years, the rapid cooling rate that the model showed was revolutionary in its effect on pegmatite geology. The article has been posted along with the essay by permission of the Mineralogical Association of Canada. David London Learn about pegmatites and join the Pegmatite Interest Group at http://www.minsocam.org/msa/Special/Pig/