Properties of Calcium and Magnesium Carbonates and their Bearing on Some Uses of Carbonate Rocks

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Abstract
A review of the available information on the physical and chemical properties of carbonate single crystals, principally calcite and dolomite, is presented as a necessary prerequisite to the understanding of limestone and dolomite. The crystal structures of the rhombohedral carbonates are well established, except for possible refinement of variable parameters, but the study of bonding has been largely restricted to C—O bonds within carbonate ions. Numerous qualitative correlations of crystal structure with specific physical and chemical properties exist, and a few successful theoretical calculations of properties from the structure have been made. Noteworthy progress has been made recently in understanding the mechanisms of structural deformation and of thermal decomposition of these minerals. Study of the properties of solid solutions, order-disorder phenomena, surface properties, and luminescence has been rather sporadic. In future, a large amount of work needs to be done in determining constants for magnesian calcite and for dolomite. The recent increased interest in the solid state promises to stimulate not only this type of investigation, but also studies involving more recently developed techniques. The physical and chemical properties of the calcite and dolomite comprising limestone, dolomite, and marble significantly affect a number of uses of these rocks. The anisotropic nature of such physical properties of the minerals as hardness, light transmission, solubility, and thermal expansion is particularly important in the utilization of the rocks for decorative and building stone. Rate of solution and solubility are also important for these uses and for others, such as agricultural limestone and acid neutralization. The chemical composition and purity of the carbonate minerals in high-calcium limestone, high-magnesium dolomite, and related marbles control the suitability of the rocks for a variety of purposes. Trace element content and certain color changes during weathering depend at least in part upon solid solution in the calcite and dolomite crystal structures. The relative ease with which calcite and dolomite decompose on heating, as in lime-making, and the physical character of the oxides produced are dependent upon the temperatures at which calcination is carried out, as well as upon the effect of added water vapor and the amount of certain salts naturally present or added. About the turn of this century interest in economic geology had reached a high level in North America. The thoughtful paper in 1893 by J. H. L. Vogt, of Norway, on injected igneous deposits derived from an igneous source by the process of magmatic differentiation, which was also advanced to account for hot mineralizing waters, drew attention once more to the earlier ideas of Elie de Beaumont. Then came the classical paper by Franz Posepny on “The Genesis of Ore Deposits” delivered before the American Institute of Mining Engineers in Chicago in 1893. This created a profound impression on American thought and stimulated a heated controversial discussion by S. F. Emmons, Van Hise, J. F. Kemp, Waldemar Lindgren, and W. H. Weed in the years 1901 to 1903, on the respective merits of heated meteoric waters versus hot juvenile waters in the genesis of ore deposits. In 1901 also came the startling new concept of secondary sulfide enrichment proposed by S. F. Emmons, Van Hise and W. H. Weed. These papers and discussions resulted in the Posepny Volume on The Genesis of Ore Deposits sponsored in 1901 by the American Institute of Mining Engineers. Geologists were rocked by the influx of new concepts and ideas bearing on the genesis of ore deposits. A forum was needed where prevailing ideas could be thrashed out and new ones presented. An idea was breeding that was shortly to give rise to another new concept—a journal of economic geology in the English language.

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