Abstract
ABSTRACTA new member of the gadolinite supergroup, gadolinite-(Nd), IMA2016-013, ideally Nd2FeBe2Si2O10, was found in the Malmkärra mine, ~3.5 km WSW of Norberg, south-central Sweden, where it occurs in association with fluorbritholite-(Ce), västmanlandite-(Ce), dollaseite-(Ce), bastnäsite-(Ce) and tremolite. Gadolinite-(Nd) forms anhedral grains up to 150 µm in size, commonly occurring as aggregates of olive green colour. The crystals are transparent with vitreous to adamantine lustre. Gadolinite-(Nd) is brittle with conchoidal fracture, no cleavage or parting was observed. It has a white streak, the Mohs hardness is 6.5–7 and the calculated density is 4.86 g cm–3. Optically, the mineral is weakly pleochroic in shades of olive green, biaxial (–), nα = 1.78(1), nβ(calc.) = 1.80, nγ = 1.81(1) measured in white light, 2V(meas.) = 62(3)°. Electron-microprobe and laser ablation inductively coupled plasma mass spectrometry analysis [in wt.%] provided SiO221.77, Y2O35.49, La2O32.78, Ce2O314.04, Pr2O33.28, Nd2O319.27, Sm2O35.30, Eu2O30.24, Gd2O34.10, Tb2O30.36, Dy2O31.32, Ho2O30.18, Er2O30.38, MgO 0.51, CaO 0.14, MnO 0.10, FeO 10.62, B2O30.10, BeOcalc.8.99, H2Ocalc.0.55 and total 99.52 giving the following empirical formula (based on 2 Si): (Nd0.632Ce0.472Y0.268Sm0.168Gd0.125Pr0.110La0.094Dy0.039Ca0.014Er0.011Tb0.011Eu0.008Ho0.008)∑1.957(Fe0.816Mg0.070Mn0.008)∑0.894(Be1.984B0.016)∑2.000Si2O9.660OH0.337. A weak Raman vibration band at ~3525 cm–1confirms the presence of water in the structure. Gadolinite-(Nd) is monoclinic,P21/c, witha = 4.8216(3) Å,b = 7.6985(4) Å,c = 10.1362(6) Å, β = 90.234(4)°,V = 376.24(6) Å3andZ = 2. The strongest X-ray diffraction lines are [dobsin Å (hkl)Irel]: 4.830 (100) 72, 3.603 (021) 37, 3.191(-112) 52, 3.097 (013) 35, 2.888 (121) 100, 2.607(113) 49, 2.412 (200) 24. Along with the Malmkärra mine, gadolinite-(Nd) was also recorded also at Johannagruvan and Nya Bastnäs. The minerals of the gadolinite subgroup together with fluorbritholite-(Ce) incorporate the highest fraction of medium-to-heavy rare-earth elements among associated rare-earth element minerals in the Malmkärra mine and possibly in all Bastnäs-type deposits.
Highlights
THE mineral gadolinite has a special place in the history of science, and so in chemistry and mineralogy
This paper provides a full characterization, including chemical composition, structural, physical and optical properties of the new mineral gadolinite-(Nd), which was approved recently by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA), under the number 2016-013
The density (Dcalc) is 4.86 g cm–3, and was calculated using the empirical formula and unit-cell parameters obtained from the single-crystal X-ray diffraction (XRD) data
Summary
THE mineral gadolinite has a special place in the history of science, and so in chemistry and mineralogy. A neodymium-dominant analogue of gadolinite(Y) or gadolinite-(Ce) was suggested by Holtstam and Andersson (2007) from Bastnäs-type skarn deposits (Bergslagen ore province, south-central Sweden), but due to the lack of a sufficient amount of material, they did not provide any data apart from the chemical microanalyses. Gadolinite-(Nd) was found in samples from the Malmkärra, Johanna and Nya Bastnäs mines, all belonging to the Fe-REE ‘Bastnäs-type’ skarn deposits in the Bergslagen ore province (Geijer, 1961; Holtstam and Andersson, 2007; Jonsson et al, 2014; Holtstam et al, 2014).
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