Djerfisherite

Djerfisherite is an alkali copper–iron sulfide mineral and a member of the djerfisherite group. The chemical composition is somewhat variable. A Russian study from 1979 on djerfisherite from the Kola Peninsula found the formula K6Na(Fe,Cu)24S26Cl, but a study in 2007 of samples from Siberia found no detectable sodium and states that the formula K6(Fe,Cu,Ni)25S26Cl is considered the most appropriate. Both crystallographic studies have 58 atoms per unit cell. Sulfur atoms are in three nonequivalent locations, containing 12, 6, and 8 atoms per unit cell. The later study put a copper atom where the earlier study put a sodium atom. More information on the structure and other questions is available, as well as 3-D models. The Webmineral "Mineralogy Database" site gives the "chemical formula" as K6Na(Fe2+,Cu,Ni)25S26Cl, apparently in error, and an "empirical formula" as K6NaFe2+19Cu4NiS26Cl. Djerfisherite is one of the rare and unusual minerals in its chemical composition, combining lithophile (K) and chalcophile (Cu,Fe,Ni) elements in its composition. In addition to djerfisherite itself, such minerals also include sodium chvilevaite Na(Cu,Fe,Zn)2S2 and murunskite K2Cu3FeS3.