The Structure of Silicate Glasses and Melts: Some Basics

Silicate glasses and melts have been of interest to mineralogists, geochemists and igneous petrologists for many decades. Silicate melts are essential components of igneous processes, participating actively in Earth differentiation, heat transfer and global geodynamics, and geochemical cycles. Melt viscosity can decrease some 20 orders of magnitude below that of corresponding solids, and timescales for transport properties are dramatically reduced in the presence of a liquid-phase. In addition, melts relevant to volcanological processes contain various amounts of volatiles, mainly H2O, CO2, and sulfur-bearing species. Models for Earth’s formation propose a period of substantial melting of the planet during the later stages of accretion, due to the extremely high energies involved in a probable Moon-forming “giant impact” event. As properties of deep magmas must be experimentally constrained, researchers studying melts and glasses participate actively in current experimental developments in Earth sciences, such as in situ experiments at high temperature (T) and high pressure (P) and numerical modeling of complex systems. Many of these experiments are designed to aid in developing an understanding at the atomic level of the structure and dynamics of silicate melts under the P–T conditions of Earth’s crust and mantle. Current issues range from the conditions of formation of planetary systems to volcanological monitoring and Earth’s dynamics. Silicate glasses and melts have been of interest in ceramic science, glass technology, and metallurgy for centuries, and more recently in the management of wastes (municipal, industrial and nuclear). A glass plant typically produces 600–1000 tons/day of silicate melts. These applications represent a major field of connection between Earth sciences and industry, and provide job opportunities for students. In addition, studies of archeological and historical glasses make them interesting as analogs for the longterm evolution of waste matrices and give insights into ancient technologies and sources of trade.