'Chayes - Observations on Chayes' discussion of the intermediate plagioclase felspars.' Comprises correspondence and notes. Includes F Chayes, 'A Possible Explanation of δc Separations in Intermediate Plagioclase', from Acta Crystallographica May 1958, together with drafts of an article written by Helen Megaw to comment on same [which was published in Acta Crystallographica in 1960]. Also includes correspondence with Prof Paul Ewald, Dr Felix Chayes, Arthur Wilson and Henry Lipson of Acta Crystallographica, Dr Michael Bown, and Dr George Brindley.