Hureaulite, Mn+25(H2O)4[PO3(OH)]2[PO4]2, from different deposits of the Totoral pegmatitic field, San Luis.

Abstract

Huréaulite, a hydrated manganese (II) phosphate mineral, has been found in three different pegmatites of the Totoral pegmatitic field, San Luis ranges, Argentina. In Santa Ana mine, a berillium-bearing pegmatite located in the Cerro La Torre group, this phosphate mineral occurs associated with eosphorite as little prismatic idiomorphic crystals implanted on sicklerite exfoliation surfaces, and originated by the hydrothermal alteration of primary lithiophilite. In Ranquel, a berillium-bearing pegmatite located in the Loma Alta group, huréaulite is associated with ferrisicklerite, purpurite, phosphosiderite, strengite, reddingite, meta-autunite, eosphorite, vivianite and hydroxil-apatite and has been formed by hydrothermal reworking of triphylite; the crystals are 5 mm in length and show typical monoclinic forms. In San Luis II, a lithium-bearing pegmatite located in the Paso del Rey group, huréaulite has been found as short prismatic crystals or thin coating layers intergrowed between fibrous dufrénite, in association with ferrisicklerite, bermanite and carbonate-fluorapatite and formed by extreme hydrothermal alteration of primary lithiophilite. The huréaulite from these different occurrences shows similar physical and optical properties, but different degrees of Fe-Mg-Ca octahedrical substitutions, according with the secondary phosphate minerals that form the assemblages.