The High-Low Inversion Behaviour of Microcrystalline Quartz Crystals

Abstract

The temperatures of structural transformations of (quartz) crystals are dependent on the degree of disorder, as has been discussed previously (III-7, 8). According to Flörke (1961) micro- and cryptocrystalline particles, being finer than a distinct grain size, should be influenced in their structural (dis-)order by the large relation particle surface/volume, because the surface of a crystal is always disturbed. Provided that the crystal to be examined is a cube with a disturbed surface layer thickness of 10 Å, after Flörke 6 volume-% of this cubic cristal will be disordered if the edge length of this crystal is 0.1 µ. In the case of an edge length of 0.01 µ, the disordered portion caused by the disturbed surface layer will be 50 volume-% of the particle. Therefore a distinct ti-dependence on the size of quartz crystallites must be expected in the case of extremely finegrained samples. Three examples given by Flörke (1961) point this out. However, data from Keith and Tuttle or Warne as well as the author’s investigations reported below show that this ti-dependence on the size of crystallites is only valid for extremely fine-grained cryptocrystalline quartz particles, while numerous quartz crystals coarser than 0.05 µ ∅ really invert at “normal” temperatures (> 570° C). This demonstrates that the portion of disorder coming from the disturbed surface layer can be neglected at least for these crystals showing ti > 570° C.KeywordsDifferential Thermal AnalysisQuartz CrystalInversion EffectQuartz StructureSecondary QuartzThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.