Tourmaline studies through time: contributions to scientific advancements

Tourmaline studies have been an integral part of science and scientific exploration for centuries and continue to flourish today. In the 19th century, the curious pyroelectric and piezoelectric properties of this mineral attracted the attention of scientists who considered tourmaline central to a grand unification of the theories of heat, electricity and magnetism. The common occurrence of tourmaline in granites and granitic pegmatites was widely known at that time, but, subsequently, tourmaline was discovered in a great range of igneous, metamorphic and sedimentary rocks and a variety of ore deposits, including hydrothermal systems. The chemical complexity of this mineral became more fully established and appreciated by the end of the 19th century. In the early- and mid-20th century, tourmaline studies greatly expanded as a consequence of the (1) exploration of wider ranges of geological settings, (2) development of instrumentation to characterize the chemical and physical properties of minerals and (3) the applications that derived from these studies. In clastic sedimentary rocks, tourmaline was identified as one of the most important heavy minerals and became a means to estimate maturity of the clastic sediment, to determine provenance and to make stratigraphic correlations. The crystallography of tourmaline was more fully understood and the overall structure and general structural formula was known by the 1960-1970's. Applications of tourmaline relied originally on its piezoelectric properties that became increasingly important during the 20th century. One application, developed after World War I, was the detection and measurement of conventional and atomic explosion pressures based on tourmaline's piezoelectric properties. Tourmaline studies have expanded in breadth and greatly increased in number since 1977, when micro-analytical and crystallographic/spectroscopic instrumentation became widely available. Petrologically, tourmaline has become a valuable petrogenetic indicator mineral in rocks and sediments due to its occurrence in most rock types, its extreme P-T range of stability, from the near surface to the deepest levels of the crust, its capacity to attain a chemical signature during the evolution of the rock in which it is formed, its ability to retain that chemical imprint, and its capability to provide specific information on the time, temperature and fluid history of its host rock. More recent studies have greatly expanded the conceptual framework of its internal structure and have dramatically increased the number of tourmaline species from 4 to 33. The future of tourmaline studies is promising with many new and exciting possibilities that will continue to influence scientific inquiry well into the future.