Forelesninger holdt ved Advanced Study Institute of Feldspar - Oslo 1962
Lectures held at Advanced Study Institute of Feldspar - Oslo 1962

As requested by the Advanced Study Institute of Feldspar, this paper will contain a review of some genetic aspects of feldspar twinning. In addition I shall make some original comments and suggestions on this subject with the aim of stimulating further research in the area. This paper will consist of three topics: the significance of twinning in microcline, the effect of structural state on the rhombic section and composition plane of pericline-twinned plagioclase, and some petrologic factors that affect the frequency and type of twinning.

I have profited greatly by extensive discussion with Professor Julian R. Goldsmith, to whom I wish to express my thanks.