STEVENSITE FROM THE KIURA MINE, OITA PREFECTURE

Abstract

Two magnesian clay minerals were found in clay veins in the country rocks of the ore deposits of the Kiura mine, Oita Prefecture. A pale pink-coloured material (sample A) is identified as a usual stevensite from its properties. The X-ray pattern of a blackish brown coloured clay (sample B) is obscure, but changes of the pattern after various treatments indicate the mineral to be a random interstratification of an expandable layer and a nonexpandable layer. Its DTA and Infra-red data are very similar to those of the sample A. Therefore, these two clay minerals are concluded as stevensites, of which the crystallinities are different mutually. Their modes of occurrence suggest that these clay minerals are hypogene in origin and formed from a hydrothermal solution charged with magnesium and silica.