Abstract

Ralstonite is renamed hydrokenoralstonite, ideally □2Al2F6(H2O). “Atroarite” and the “AHF” phase (hydrated aluminum hydroxy-fluoride, a “ralstonite-like mineral”) are also hydrokenoralstonite. The name ralstonite is transferred to the group, where M3+ cations are dominant at the B site, and Al is dominant among them, and F1– is the dominant anion at the X site. Hydrokenoralstonite from the Pitinga mine, Presidente Figueiredo, Amazonas, Brazil, is intimately associated with galena and sphalerite. It forms chemically homogeneous octahedral crystals, from 0.1 to 1 mm in size. The mineral is colorless with white streak, vitreous luster, transparent, density (calc.): 2.554 g/cm3. Its empirical formula is (□1.87Na0.12Rb0.01)Σ2.00(Al1.86Mg0.14)Σ2.00[F3.46(OH)2.54]Σ6.00(H2O). The mineral is cubic, forumla (#227), a 9.8455(7) Å, V 954.36 (12) Å3, Z = 8. Hydrokenoralstonite exhibits (Al,Mg) cations with octahedral coordination and Na cations located within distorted cubes. Coulsellite, a rhombohedral pyrochlore-supergroup mineral, ideally (Na,Ca)2(Mg,Al)2F6F, is renamed fluornatrocoulsellite, and the name coulsellite is transferred to the group, where M2+ cations are dominant at the B site, and Mg is dominant among them, and F1– is the dominant anion at the X site. This nomenclature proposal was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association.

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