Progress in mineralogy

SUMMAaY. The Mineralogical Society celebrated its 5oth Anniversary in I926; this address attempts to summarize the substantial developments in the subject over the past 5o years and looks ahead to the future. Up to 1926, only the techniques of goniometry, optical investigation of non-opaques, and classical chemical analysis had been fully exploited. X-ray crystallography, though already I4 years old, had made little impact but was to advance with great rapidity to achieve, for example, the modern conception of silicate structure by I934. The insight into the atomic structure of minerals provided by this technique has been central to the advancement of the subject. The powder camera and more recently the counting diffractometer have become the chief determinative tools, though micxoscopy is still important. Diffractometry with a tied computer has greatly speeded up structural work. Advances in electron microscopy may soon make it possible to produce direct images of atomic structure. Meanwhile wet-chemical procedures have largely given place to spectroscopy (optical emission, X-ray, and atomic absorption), to the electron microprobe and to various still more advanced techniques, including the investigation of stable and unstable isotopic composition by mass spectrometry. Independently, the optical identification of opaque minerals has been brought to an advanced state. All these developments have opened the way for progress in the understanding of the paragenesis and genesis of minerals, subjects to which experimentation at high temperatures and pressure now contribute materially; and for practical applications in many fields, including ore deposits, beneficiation, ceramics, refractories, cement, sinters, and fuels.