Abellaite, NaPb2 (CO3)2 (OH), a new supergene mineral from the Eureka mine, Lleida province, Catalonia, Spain

Abstract

The new mineral abellaite (IMA 2014-111), ideally NaPb 2 (CO 3 ) 2 (OH), is a supergene mineral that was found in one of the galleries of the long-disused Eureka mine, in the southern Pyrenees (Lleida province), Catalonia, Spain. Abellaite is found as sparse coatings on the surface of the primary mineralization, it forms subhedral crystals not larger than 10 μm as well as larger pseudohexagonal platelets up to ∼30 μm. Individual crystals commonly have a tabular to lamellar habit and form fairly disordered aggregates. The mineral is associated with a large number of primary minerals (roscoelite, pyrite, uraninite, coffinite, ‘carbon’, galena, sphalerite, nickeloan cobaltite, covellite, tennantite and chalcopyrite) and supergene minerals (hydrozincite, aragonite, gordaite, As-rich vanadinite andersonite, cejkaite, malachite and devilline). Abellaite is colourless to white, with a vitreous to nacreous lustre. The mineral is translucent, has a white streak and is non-fluorescent. The aggregates of microcrystals are highly friable. The calculated density using the ideal formula is 5.93 g/cm 3 . The chemical composition of the mineral (the mean of 10 electron microprobe analyses) is Na 3.88, Ca 0.29, Pb 72.03, C 4.17, O 19.47 and H 0.17, total 100.00 wt% (H, C and O by stoichiometry assuming the ideal formula). On the basis of 7 O atoms, the empirical formula of abellaite is Na 0.96 Ca 0.04 Pb 1.98 (CO 3 ) 2 (OH). The simplified formula of the mineral is NaPb 2 (CO 3 ) 2 (OH). The mineral is hexagonal, space group P 6 3 mc , a = 5.254(2), c = 13.450(5) A, V = 321.5(2) A 3 and Z = 2. The strongest powder-diffraction lines [ d in A ( I ) ( h k l )] are: 3.193 (100) (0 1 3), 2.627 (84) (1 1 0), 2.275 (29) (0 2 0), 2.242 (65) (0 2 1, 0 0 6), 2.029(95) (0 2 3). Abellaite has a known synthetic analogue, and the crystal structure of the mineral was refined by using crystallographic data of the synthetic phase. The mineral is named in honour of the mineralogist and gemmologist Joan Abella i Creus (b. 1968), who has long studied the deposits of the Eureka mine and who collected the mineral.