Earth Materials
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rvations were the first clues to understanding the internal structure of solids. Steno was also a keen geological observer. He is given credit for the first statement of the law of superposition of sedimentary strata. The first quantitative experiments on the origin of minerals grew out of studies of glass and ceramics. French mathematician Rene-Antoine Ferchault de Reaumur (1683-1757) tried to determine the composition of Chinese porcelain by melting minerals and rocks. So, for at least the past 300 years, there has been a constant interplay between the findings and techniques of Earth scientists and mate1 rials scientists (see Hazen for a good historical survey). In more recent times, the historical connection is clear. As an example, the Department of Materials Science in the School of Engineering at Stanford University traces its lineage back through the physical metallurgy section of the Division of Mining and Metallurgy, which was part
MRS BULLETIN/MAY 1992
of the School of Mineral Sciences (now the School of Earth Sciences), home to its sister division, Geology. At Penn State, the College of Earth and Mineral Sciences combines ceramic, materials and polymer sciences with mineral engineering and Earth sciences. The combination of materials science and Earth sciences is a natural one, and these two disciplines periodically rediscover one another, and in doing so, invent new labels — a recent one being "mineral physics." Our selection of topics for this issue has been guided by a desire to focus on some of those critical areas of overlap
The combination of materials science and Earth sciences is a natural one. between mineral physics and materials science. We have tried to cover the full range of Earth environments. W.H. Casey and his colleagues summarize some of the important aspects of surface chemistry in controlling reactions that occur within the first few tens of meters of the Earth's crust. Surface chemistry has a major impact on our understanding of groundwater and ocean compositions—and the implications for studies in environmental geochemistry are so many that such processes are a topic 2 of a special volume. Additionally, one should note that over geological time periods, highly ordered low-temperature phases form that cannot be easily synthesized in the laboratory; thus, natural environments can be an important source of unusually large or complex crystals. A. Navrotsky and colleagues describe another temperature and pressure regime that perhaps remains a unique domain to Earth scientists —the formation of high-pressure phases at depths of 400 to 1,000 km, where the Earth reaches pressures of 150,000 to 300,000 atmospheres
(15-30 GPa) and temperatures of up to 2000 K. Some of the high pressure phenomena, e.g., the crystalline-to-amorphous transition, find analogues in features described by L.M. Wang and R.C. Ewing in their contribution summarizing the results of ion irradiation of complex silicates. There are important parallels between the topological and compositional controls of pressure-induce
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