Monazite is a common trace mineral in metamorphic rocks, and is critical for age determinations. The Light Rare-Earth Elements (LREEs) are a main chemical constituent of monazite, yet the host of LREEs before monazite forms in a rock is unclear. Using natural samples from Great Smoky Mountains National Park, this work will discriminate whether LREEs are hosted by major silicate minerals or LREE-rich trace minerals such as allanite. The work will also show whether monazite forms instantaneously or has a protracted growth history. These results will help characterize monazite-forming reactions to improve our understanding of the ages monazite provide, and better constrain the tectonic processes that produced the Smokies and other mountain belts. Results will also be used to improve interpretive aids for the 10 million people that visit the Great Smoky Mountains National Park each year.