Interesting specimens of potassium feldspars in the Museum of the Mining Institute

Abstract

First of all, interest was aroused by the huge Baveno twin of orthoclase from the vicinity of Kyakhta, depicted in Fig. 1, and not only due to the clarity of its formation, but also because of the beautiful almandine crystals included in it. A special optical study carried out by V.I. Sokolov showed that the orthoclase substance is intergrown by plagioclase at No. 5, forming well-developed polysynthetic twins according to the albite law, with one individual of the twin being conformably brunted with the orthoclase substance

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