![]() The influence of small variations in Na-LTA bulk stoichiometry on the rate and course of the thermal transformation process was examined. In this work we investigated the conditions under which pure basic hexagonal nepheline phase is formed by the zeolite Na-LTA thermal transformation route. Empirical formulae (EMPA analysis) are very close to the ideal compositions with traces of Ca and K for trinepheline, and of Ca, K, Ba, Mg, Fe, and Mn for fabriesite. They are white to yellowish in hand specimen, colourless in thin section the streak is white and the lustre appears vitreous to greasy they are non-fluorescent Mohs' hardness is 5–5½. Both fabriesite and trinepheline are pseudomorph after jadeite and occur as skeletal allotriomorphic crystals up to 15–20 μm long and 5–10 μm wide. All phases have been identified via electron backscatter diffraction (EBSD) patterns. Fabriesite and trinepheline occur intimately intergrown together with nepheline, more rarely with albite and other feldspar-group phases such as banalsite and stronalsite other associated minerals are jadeite and secondary products like natrolite and harmotome. Fabriesite is named in memory of Jacques Fabriès (1932–2000), former professor of the “Muséum National d'Histoire Naturelle” in Paris (France). The name trinepheline is known in literature for the polymorphs of synthetic NaAlSiO4 with a value of the c parameter that is three times that of nepheline. ![]() ![]() Both minerals and their names were approved by the IMA Commission on New Minerals and Mineral Names (IMA 2012–024 and IMA 2012–080). ![]() Two new mineral species, trinepheline (NaAlSiO4) and fabriesite (Na3Al3Si3O122H2O), are described from late-stage metamorphic veins of the jadeite deposit of Tawmaw-Hpakant (Myanmar). ![]()
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