Diaplectic glass

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Diaplectic glass forms when the lattice structure of a crystal is destroyed by extreme pressures in the form of shock waves without passing through a liquid phase.

Such shock waves can, for. B. arise with a very large meteorite impact ( impact metamorphosis ). But also underground atomic bomb tests can produce diaplectic glass ( see also: Metamorphosis (geology) ). This behavior is in contrast to the formation of conventional glass that is melted. The result is also an amorphous body, which, however, did not result from melting and solidification.

Diaplectic glasses can be found, for example, in the vicinity of meteorite craters such as the Nördlinger Ries , where an extraterrestrial body struck about 15 million years ago. They are considered to be a special type of impact glasses that result from a shock wave metamorphosis, but are differentiated from these and the tektites . The other impact fused glasses are also created in the event of large impacts, but they are created by melting and rapid cooling of rock material like conventional rock glasses. This results in the following distinguishing features between diaplectic glasses and fused glasses:

  • Diaplectic glass remains in the rock in the position in which the original mineral was, and it differs from this essentially in its optically isotropic behavior, while the external shape (crystal boundaries, cracks) of the original mineral is retained.
  • A glass phase that was actually melted, on the other hand, is mobile and often shows corresponding flow textures (regulated inclusions, elongated gas bubbles).
  • Diaplectic glass does not contain gas bubbles; fused glass can contain gas bubbles.
  • Density and refractive index are higher for diaplectic glass than for fused glass of the same composition.

Diaplectic glass can e.g. B. from quartz crystals or feldspars . In maskelynite but from meteorites is quenched Plagioklasschmelzen.

Individual evidence

  1. ↑ Roland Vinx: Rock determination in the field. Elesevier, Munich 2005, ISBN 3-8274-1513-6 , p. 33.
  2. ↑ W. v. Engelhardt, D. Stöffler: Stages of Shock Metamorphism in Crystalline Rocks of the Ries Basin, Germany . In: B. French, N. Short (Eds.): Shock Metamorphism of Natural Materials . Mono Book, Baltimore 1968, pp. 159-168 .
  3. ↑ M. Chen, A. El Goresy: The nature of "maskelynite" in shocked meteorites: not diaplectic glass but a glass quenched from shock-induced dense melt at high-pressures. In: 62nd Annual Meteoritical Society Meeting, 11. – 16. June 1999, Johannesburg . 1999 ( usra.edu [PDF; 14 kB ; accessed on September 29, 2019]).

swell

  • Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 .