Ralstonite Renamed Hydrokenoralstonite, Coulsellite Renamed Fluornatrocoulsellite, and Their Incorporation Into the Pyrochlore Supergroup

Abstract

Abstract Ralstonite is renamed hydrokenoralstonite, ideally □ 2 Al 2 F 6 (H 2 O). “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 M 3+ cations are dominant at the B site, and Al is dominant among them, and F 1– 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/cm 3 . Its empirical formula is (□ 1.87 Na 0.12 Rb 0.01 ) Σ2.00 (Al 1.86 Mg 0.14 ) Σ2.00 [F 3.46 (OH) 2.54 ] Σ6.00 (H 2 O). The mineral is cubic, (#227), a 9.8455(7) A, V 954.36 (12) A 3 , 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) 2 F 6 F, is renamed fluornatrocoulsellite, and the name coulsellite is transferred to the group, where M 2+ cations are dominant at the B site, and Mg is dominant among them, and F 1– 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.