Natromontebrasite, a Discredited Mineral Species

Abstract

Two samples of "natromontebrasite", among which a fragment of the type material, were re-investigated by X-ray-diffraction 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 heterogeneously 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)AlPO 4 (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. SommaireDeux échantillons de "natromontebrasite", parmi lesquels un fragment du matériau type, ont été examinés à nouveau par diffraction des rayons X et par analyses chimiques. Les diffractogrammes de poudre montrent clairement la présence de lacroixite et d'autres raies, faiblement intenses, pourraient être attribuées à la wardite. Les analyses à la microsonde électronique prouvent que Na est distribué de façon hétérogène dans ces échantillons et qu'il est essentiellement localisé dans la lacroixite, elle-même dispersée dans un minéral de la série isomorphe montebrasite -amblygonite. La "natromontebrasite", initialement décrite comme (Na,Li)AlPO 4 (OH,F), doit donc être considérée comme un mélange d'amblygonite riche en OH et de lacroixite, avec de la wardite accessoire. La discréditation de la "natromontebrasite" a été approuvée par la Commission des nouveaux Minéraux et Noms de Minéraux de l'IMA.

An association of secondary Al-Li-Be-Ca-Sr phosphates in the San Elias pegmatite, San Luis, Argentina

“…Baldwin et al (2000) established an alteration sequence for Karibib pegmatites with amblygonite ! montebrasite and low-F montebrasite -"natromontebrasite" (now discredited; Fransolet et al 2007) -fluorapatite ! brazilianite !…”

Secondary phosphates in montebrasite and amblygonite from Nagatare, Fukuoka Prefecture, Japan

“…Ab, albite; Amb, amblygonite; Mtb 2 , secondary low-F montebrasite; Lcx, lacroixite. mined to be a mixture of an OH-rich amblygonite and lacroixite (Fransolet, 1989;Fransolet et al, 2007). The montebrasite-amblygonite series is topologically identical to the lacroixite structure, and Na could not substitute Li at low temperatures in the montebrasite-amblygonite structure (Groat et al, 1990) (Table 3).…”

Crystal chemistry of the divalent cation in alluaudite-type phosphates: A structural and infrared spectral study of the Na1.5()1.5Fe1.5(PO4)3 solid solutions (x=0 to 1, M2+=Cd2+, Zn2+)

“…The introduction of Zn 2+ in alluaudite-type phosphates was not previously reported in the literature, but natural arsenates johillerite, Na(Mg,Zn) 3 Cu 2+ (AsO 4 ) 3 , and o'danielite, Na(Zn,Mg) 3 H 2 (AsO 4 ) 3 [39], as well as the synthetic compound AgZn 3 H 2 (AsO 4 ) 3 [22], show significant amounts of this cation. Moreover, chemical analyses of natural alluaudites frequently contain small amounts of Zn 2+ , which can reach 0.29 wt% ZnO [4,[40][41][42][43][44].…”