NATROMONTEBRASITE, A DISCREDITED MINERAL SPECIES

Two samples of “natromontebrasite”, among which a fragment of the type material, were re-investigated by X-ray-diffrac-tion techniques and chemically analyzed. The X-ray powder-diffraction patterns clearly show the presence of lacroixite, whereas additional weak peaks are tentatively attributed to wardite. Electron-microprobe measurements confirm that Na is heteroge-neously distributed within the samples, and essentially located in domains of lacroixite, itself scattered in a mineral of the montebrasite–amblygonite solid-solution series. “Natromontebrasite”, originally described as (Na,Li)AlPO4(OH,F), must thus be considered as a mixture of an OH-rich amblygonite and lacroixite, with subordinate amounts of wardite. The discreditation of “natromontebrasite ” has been approved by the IMA Commission on New Minerals and Mineral Names