TEM-investigation of the sanidine/microcline transition across metamorphic zones : the K-feldspar varieties
Bambauer, Hans Ulrich; Krause, Christian
published: Mar 21, 1989
ArtNo. ESP147050101008, Price: 29.00 €
Abstract The diffusive transformation sanidine ±^: microcline results in transformation pseudomorphs which display a variety of submicroscopic to microscopic K-feldspar intergrowths. According to the scale and nature of the intergrowths, as well as the method of investigation, several K-feldspar varieties may be distinguished. From a TEM-study of about 70 samples taken across a regional metamorphic zone and a contact metamorphic aureole, the K-feldspar components of the observed perthites can be classified by their TEM contrast and diffraction pattern into the varieties sanidine, "tweed" orthoclase, irregular microcline, and regular microcline. In order to reduce the confusion in K-feldspar definitions, an attempt is made to correlate these "TEM varieties" with the "optical varieties" sanidine, orthoclase, and microcline as well as the "X-ray varieties" sanidine, X-ray orthoclase, intermediate microcline, and low microcline. In addition, they are compared to the K-feldspar modifications sanidine and (low) microcline. An interpretation of the different Al,Si ordering paths, which may be deduced from X-ray and electron diffraction data, is also given.