Crystal chemistry of ZnS minerals formed as high-temperature volcanic sublimates: matraite identical with sphalerite

The crystal chemistry of ZnS minerals formed as high-temperature volcanic Sublimates from lwodake volcano, Satsuma-lwojima, Japan, has been studied by means of single-crystal X-ray diffraction (XRD), electron microprobe (EMP), micro-XRD, and micro-Raman scattering analyses. These minerals were identified as sphalerite and matraite by using a four-circle automated X-ray diffractometer. However, these two minerals were virtually the same in XRD pattern, chemical composition and micro Raman-scattering Spectrum. A close examination of the observed reflections for the matraite sample revealed that all of them can be identified as reflections diffracted from (001)-twinned matraite. Moreover, all the reflections from (001)-twinned matraite were completely identical with those from (111)-twinned sphalerite. Consequently, it is evident that matraite is not a distinct mineral species but can be treated as (111)-twinned sphalerite. Occurrences of this twinned sphalerite may be characteristic of high-temperature volcanic sublimates.