Abstract
Abstract Sanidine single crystals from Volkesfeld/Eifel (Germany) exhibit an unusually rapid Si, Al exchange on annealing at temperatures above 1023 K. X-ray topographic studies (Lang technique) before and after annealing show that large volumes (up to several cm3) of the crystals are highly perfect. There are few defects only (growth striations, growth-sector boundaries, grown-in dislocations), and Pendellösung fringes can be observed. While the Si, Al-exchange rate is reduced by annealing, the growth striations and Pendellösung fringes vanish, and for certain reflections, e.g. (002), the diffracted intensity is increased due to reduction of the “dynamical” extinction. These changes are illustrated by selected X-ray topographs.
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