On the structure of epidote

Abstract

The structure of epidote, HCa~(A1, Fe)ALSi3Ola, has been refined by two-and three-dimensional syntheses. The revised structure, in favour of which an earlier proposal was withdrawn, has now been confirmed. The structure is of the mixed silicate type containing both SiO 4 and SilO 7 groups bound together by Al, Al(Fe), Ca and O atoms and OH groups. Epidote is an alumino-silicate, like cyanite etc., as the A1 and O atoms and OH groups form octahedral chains which occupy the bulk of its structure.