Crystallographic studies have long made use of spectroscopic techniques such as electron microprobe, x-ray fluorescence, Mossbauer, and Fourier transform infrared spectro- scopy, but these methods have rarely been applied together in a complementary fashion to petrologic problems. Proposed work seeks to further develop and utilize the capabilities of these methods to study biotites within a petrologic framework. Major and minor elements, Fe 3+, Fe 2+, OH, and octahedral ordering will be examined in two suites of biotites and coexisting minerals from western Maine and northern Idaho. Spectroscopic data will be used to study the cation site occupancies and resultant crystal structures of biotites, as well as the influence of mineral assemblage on biotite composition. Results will be used to evaluate the effects of Fe 3+ and octahedral ordering in minerals on activity models and geothermometers. Most importantly, a new unified substitution model will be sought in order to explain the compositional variation of biotite as a function of metamorphic reactions and mineral assemblage.
