Early X-ray studies showed that the crystal structure of cobaltite must be closely related to that of pyrite. The space group of pyrite is Pa3. and the unit cell contains 8S. In cobaltite these must be replaced by 4As+4S, and this leads inevitably to the space group P213. MECHLING (1921) realized this, and it was consequently assumed that cobaltite (and gersdorffite) had the same crystal structure as ullmannite, whose external crystal form was known to agree with the point group 23.