Master of Science (MS)


Geology and Geophysics

Document Type



Tourmaline is a petrologic indicator mineral that is the major repository of boron in the earth’s crust. It forms readily when boron is present, accommodating multiple cations and anions with multiple possible substitutions for each site in the crystal structure. It is stable over a wide variety of pressures and temperatures, from near-surface P/T conditions to greater than 950 C and 7 GPa. It records information about conditions of formation, as well as pressure and temperature. Due to its resistance to chemical or physical weathering, and the negligible diffusion of elements in the crystal lattice, information about provenance is preserved. In Henry and Guidotti (1985), major elements of tourmaline were used to construct ternary diagrams that classify tourmalines according to provenance. However, this technique does not make use of the entirety of available chemical data. New statistical techniques can make use of all available chemical information and provide information about element importance. Using a novel application of an existing statistical method, random forests, to high-dimensional tourmaline data, provenance information is obtained. Existing chemical analyses are assembled into a database and labeled with their provenance. A random forest is ‘grown’ using a full database of tourmaline data, producing a set of rules for classifying tourmalines according to provenance. The random forest method has internal controls on accuracy and fitting of the data, and is capable of classifying tourmalines at a level of between 90 and 95% accuracy. As an independent test, a random forest built from this database is used to successfully classify tourmalines according to provenance.



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Committee Chair

Henry, Darrell