Rosickyite, the natural monoclinic gamma -form of sulphur, exists in
only a few localities around the globe. In the old asphalt mine at La
Presta, Neuchatel. Switzerland, rosickyite occurs locally as small, but
very well formed crystals suitable for crystallographic studies. It
grows as an alteration product of pyrite-rich asphalt. Rosickyite from
La Presta mine is pure molecular sulphur, as revealed by gas
chromatography-mass spectrometry. The X-ray powder diffraction data of
La Presta rosickyite does not match the one previously published for
this species. Therefore, a single crystal study was undertaken and a new
indexed X-ray powder diffraction diagram for natural rosickyite is
proposed.