Experimental mineralogy : achievements and prospects

Abstract

Part I : One aspect of the progress in experimental mineralogy, the capability of sustaining in the laboratory the pressures and temperatures believed to exist in the earth, is reviewed, from Réaumur (1727) to the present. The dominance of the French schools in the earliest period of growth, the impact of Sir James Hall's study of the melting of calcite under pressure, the evolution of the principles of phase equilibria and their application to phase diagrams, and the importance of eutectics and crystal fractionation are highlighted. The early history of the quenching technique used in examining high-temperature phase equilibria, the pioneering development of apparatus that could withstand relatively high pressures, and the recognition of the role of volatiles in mineral synthesis and growth are described. The major developments of high-pressure apparatus include externally and internally heated gas-media devices, solid-media pressure vessels, simple squeezers, and the related diamond-anvil, high-pressure cells. Conditions equivalent to those at the core-mantle boundary can now be sustained in the laboratory. Part II : As a result of the dramatic developments in high-pressure and high-temperature apparatus as well as in a wide variety of characterization techniques, at least eight major areas of basic research in experimental mineralogy are believed to be appropriate for expanded effort. These include (1) synthesis and characterization of mirerals and mineral assemblages stable in the mantle and core, (2) measurement of crystal structure at high pressures and temperatures simultaneously, (3) determination of the structure of silicate liquids and development of theories for nucleation and melting, (4) kinetics of mass transfer in crystals and liquids including crystal zoning, order-disorder, metasomatism, aggregation, convection, and mixing of magmas, as well as the diffusion and infiltration of elements through porous media under both stressed and hydrostatic conditions, (5) study of materials of minute dimension, especially the groundmass of igneous rocks, sea-bottom sediments, fibers, and clays, (6) characterization of organic minerals such as those in coal and particularly determination of the influence of living organisms on the growth of inorganic crystals (biomineralization), and (7) study of silicate systems in hydrogen at low pressures, simulating the condensation and aggregation of the primordial earth. The challenge of the future is primarily the discovery of mineral resources for the use of mankind. Basic research in (8) the principles of element concentration is considered the most important contribution to be made by the next generation of experimental mineralogists.