On some unusual twin-laws observed in the orthoclase crystals from Goodsprings, Nevada

Abstract

The very abundant literature dealing with the twinning of felspar phenocrysts has put on record a surprisingly large number of twin-laws. Some of these have such complex indices that they have never been accepted; others are regarded as doubtful. Yet the authors of these have well-established reputations and the accuracy of their observations cannot be doubted. The difficulty lies in the interpretation of the results. Beside numerous examples of well-defined laws, one comes across a high percentage of isolated cases, each appearing quite as plausible as these, yet difficult to assign to any definite law.