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November-December 2013

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Crystal-Filled Cavities in Granitic Pegmatites: Bursting the Bubble

In November 1991, Louis B. Spaulding Jr. (deceased 2013) invited me to his Little Three pegmatite mine near Ramona, California, to view the last of a string of crystal-filled miarolitic cavities that he had been mining from the main pegmatite dike on the property (see London et al. 2012 for additional details of the mine). Spaulding had been mining northward up a steeply dipping portion of his pegmatite, and the last of the pockets was beneath an oak tree whose roots encircled crystals of smoky quartz and lepidolite (fig. 8–15 of London 2008). The pocket wall was friable to the east (90 degrees off the trend that Spaulding had been following), so I started digging in that direction with a screwdriver. After removing approximately 20 cm of loose brecciated pegmatite, an open space appeared. As I explored the space with my hand, I felt crystals so large that I could not grasp them. The first crystal that was small enough to bring through the portal was a Coke-can-sized green tourmaline crystal with topaz and albite around its base (fig. 8–16 of London 2008).

Dr. David London is a Stubbman-Drace Presidential Professor, Norman R. Gelphman Professor of Geology, and director of the Electron Microprobe Laboratory at the University of Oklahoma.

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