Showing papers in "American Mineralogist in 1974"

High Resolution Electron Microscopy of Silicates

Abstract: Imaging of crystal structures of minerals clearly shows details within ideally periodic regions, even at the unit cell scale. A variety of crystal imperfections can be observed at point-to-point resolutions down to 3A-intermediate between bond lengths and unit cell dimensions. Fluctuations in both structure and composition can be observed in volumes up to 14 orders of magnitude smaller than is possible by standard single crystal X-ray techniques. We have obtained crystal structure images of the following silicate structure types: "ring" structures (beryl and cordierite), isolated and paired tetrahedra (idocrase), single and double chains (orthoenstatite and hornblende), framework (scapolite), and sheet (muscovite). Regular and perturbed regions containing defects are clearly differentiable. Antiphase domains (hornblende) and stacking faults (enstatite) as well as the effects of radiation damage produce recognizable structural effects, only some of which are reflected in the electron diffraction patterns. An example of the usefulness of the technique is the resolution of small regions (several unit cells wide parallel to [100D of clinoenstatite intergrown within orthoenstatite. The technique of high resolution electron microscopy has great potential for mineralogy and geology. Solid solution series may well be resolvable into stoichiometric phases differing only slightly in both composition and/or structure. Homologous phases, potentially resolvable by electron microscopy, have the possibility of providing far more sensitive mineralogical indicators to past history and environments than currently exist.