Abstract: Corkite associated with plumbojarosite and goethite occurs in gossan and iron-formation at Black Mountain and Broken Hill, Aggeneys. Electron microprobe analyses indicate that there are two groups of corkite present in the area; one with high Cu and low (PO₄)³⁻ and the other with low Cu and high (PO and the other with low Cu and high (PO₄)³⁻ contents. This can be explained in terms of the general formula contents. This can be explained in terms of the general formula AB₂(XO₄)₂(OH)₆, where the incorporation of divalent ions in the B site is accompanied by the exchange of trivalent anions by divalent ones to retain charge balance. Complete solid-solution is inferred between (SO₄)²⁻and (PO₄)³⁻ end members, indicating that the jarosite and beudantite groups form part of the same solid-solution series. The distribution of Zn in corkite also reflects the regional distribution of zinc grades in the area, becoming more zinc-rich from west to east. New X-ray diffraction parameters are also presented which update existing data.