Abstract
SOME ten years ago when grinding down a thin slice of limestone under water I was surprised to find that the operation was accompanied by faint flashes of light which seemed to issue from certain spots of superior hardness; on examining the slice under the microscope it was found that these spots consisted of quartz. This led me to devise an apparatus by which the luminescence could be continuously produced and so rendered a subject for precise observation. The substance to be examined was attached to the free end of a hinged bar and adjusted so that it rested against the edge of an emery, or, still better, a carborundum, wheel which was rotated by an electric motor. Of some forty minerals experimented upon no fewer than eighteen emitted light while being ground. Those that did not included all the sulphides which were examined, viz. zinc blende, cinnabar, antimonite, galena, copper pyrites, and arsenical pyrites. Iron pyrites, of course, yielded sparks, but these were not accompanied by tribo-luminescence. Almost all the silicates emitted light, e.g. orthoclase, labradorite, idocrase, garnet, tourmaline (one variety, another did not), epidote, zircon, topaz, and glass; several oxides, e.g. corundum, magnetite hæmatite, cassiterite, quartz, and flint; light was also obtained from wavellite, apatite, celestine, and barytes. But the most remarkable results were obtained from fluorspar; all the varieties of this mineral which were examined gave light, but one in particular, distinguished by its green colour, emitted blue light, not only in great quantity, but also of such persistency that the whole periphery of the wheel was alive with it.
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SOLLAS, W. Luminosity by Attrition. Nature 106, 438 (1920). https://doi.org/10.1038/106438c0
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DOI: https://doi.org/10.1038/106438c0
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