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October 2011 - Tourmaline
From the Vikings’ sunstone to a modern piezometric pressure sensor, tourmaline is an intriguing mineral with a new degree of significance. Tourmaline was considered by 18th century physicists as the key to a grand unification theory relating heat, electricity, and magnetism, but new studies define its role as an indicator of Earth’s processes. With its plethora of chemical constituents and its wide stability range, from near-surface conditions to the pressures and temperatures of the mantle, tourmaline has become a valuable mineral for understanding crustal evolution. Tourmaline encapsulates a single-mineral thermometer, a provenance indicator, a fluid-composition recorder, and a geochronometer. Although also prized as a gemstone, tourmaline is clearly more than meets the eye.
December 2013 - Garnet: Common Mineral, Uncommonly Useful
Garnet is among the most studied—and most beloved—minerals, owing to its commonality in diverse geologic contexts, its often large euhedral crystals, its sometimes dazzling colors, and its propensity for preserving information about its growth history. Chemically zoned garnet represents a remarkable tool for deciphering metamorphic conditions and the evolving tectonic processes that drive garnet growth over many millions of years. In the deep Earth, garnet is a key rock-forming mineral, influencing the physical properties of the mantle and the composition of mantle-derived magmas. Garnet has been sought for ages as a semiprecious gemstone (the birthstone of January) and has been mined or synthesized (including nonsilicate garnet) for industrial purposes, including laser, magnetic, and ion-conductor technology. This issue of Elements will emphasize the most recent innovations in thermodynamic, geochemical, geochronologic, and industrial applications of garnet, while providing perspective on decades of garnet-related research.