The crystal structures of jarosite and svanbergite

The crystal structures of jarosite and svanbergite have been refined. It was revealed that geometry of the sulphur tetrahedra in jarosite and alunite is much affected by the octahedral cations. The sulphur tetrahedra in jarosite expand nearly to maximum, and they are comparable in size to those of phosphorus tetrahedra. The six refined crystal structures of the alunite-type minerals, alunite, goyazite, crandallite, woodhouseite and these two minerals, are compared. It was found that jarosite which has Fe octahedra behaves in an exceptional manner. It seems that the geometry of other five structures which have Al octahedra is in right order from the view point of crystal chemistry.