Abstract

Abstract The optical behaviour of artificial autunite crystals was studied in connection with its water content. The autunite was shown to be transformed into meta‐autunite‐I on loosing water. The crystal structure of both compounds was studied by means of X‐rays. The remarkable properties of the mineral, namely its varying water content and the base exchange are associated with the crystal structure. By studying the corresponding Ba‐compound it is concluded that the cations in the meta‐autunite‐I probably do not occupy a fixed position. Because of their great mobility it is permissible to consider them as “vagabond ions”.