Mckelveyite group minerals – Part 1: Nomenclature and new data on donnayite-(Y)

Abstract

The mckelveyite group consisting of seven carbonate minerals – mckelveyite-(Y), ewaldite, weloganite, donnayite-(Y), alicewilsonite-(YCe), alicewilsonite-(YLa), and bainbridgeite-(YCe) – is formally established. The general formula of the minerals is A3B3(CO3)6 ⋅ 3H2O, where A= Na, Ca, Y, and Zr and B= Sr, Ba, Ce, and La. Different order–disorder modifications are known resulting in triclinic, monoclinic, hexagonal, and trigonal minerals with essentially the same structure. Re-examination of donnayite-(Y) type specimens shows that the original description contains data collected on two different species: donnayite-(Y) and alicewilsonite-(YCe). Donnayite-(Y), NaCaSr3Y(CO3)6 ⋅ 3H2O, was found in only one specimen out of seven – CMNMC 39396 – housed at the Canadian Museum of Nature, Ottawa. This specimen becomes the holotype of donnayite-(Y). The crystal structure of donnayite-(Y) was solved and refined to R1= 0.055 for 3366 reflections with I>2σ(I). Donnayite-(Y) is shown to have a weloganite-type structure confirming its place in the mckelveyite group.