Abstract
Heulandites newly described from Chichijima, the Ogasawara Islands are characterized by higher Si and monovalent cation contents and by higher refractive indices and larger 2Vz as compared with ordinary heulandite, and therefore have intermediate properties between ordinary heulandite and clinoptilolite.
They are divided into two groups based on chemical composition and thermal behavior. According to the classification of Alietti, one group is regarded as heulandite type 1 and the other as heulandite type 2. The latter has higher Si content and more thermally stable framework structure than the former.
The zeolitization to form heulandite is inferred to take place as a result of the devitrification of vitreous host rocks by the actions of deuteric solution and/or the later hydrothermal solution.
