Occurrence of sekaninite associated with osumilite from Hayato and Sakkabira, Kagoshima Prefecture, Japan

Abstract

The occurrence, optical properties and morphology of the "cordierite" from Sakkabira was described by Morimoto and Minato (1949). Miyashiro (1956) noticed that the mineral is distinct from cordierite and described it as a new mineral osumilite. On the other hand, we discovered that some type of "osumilite" is actually a Fe-rich variant of cordierite, i.e., sekaninite. While modes of occurrence of osumilite and sekaninite are exactly the same, sekaninite exhibits simpler crystal morphology formed by pseudo-hexagonal {100} and {001} faces, and it is almost always covered with brownish-red iron-oxide or -hydroxide.