Nestolaite, CaSeO₃·H₂O, a new mineral from the Little Eva mine, Grand County, Utah, USA

Abstract

Nestolaite (IMA 2013-074), CaSeO3·H2O, is a new mineral species from the Little Eva mine, Grand County, Utah, USA. It is named in honour of the prominent Italian mineralogist and crystallographer Fabrizio Nestola. The new mineral was found on sandstone matrix as rounded aggregates up to 2 mm across and up to 0.05 μm thick consisting of tightly intergrown oblique-angled, flattened to acicular crystals up to 30 μm long and up to 7 μm (very rarely up to 15 μm) thick. Nestolaite associates with cobaltomenite, gypsum, metarossite, orschallite and rossite. The new mineral is light violet and transparent with a white streak and vitreous lustre. The Mohs hardness is 2½. Nestolaite is brittle, has uneven fracture and perfect cleavage on {100}. The measured and calculated densities are Dmeas. = 3.18(2) g/cm3 and Dcalc. = 3.163 g/cm3. Optically, nestolaite is biaxial positive. The refractive indices are α = 1.642(3), β = 1.656(3), γ = 1.722(6). The measured 2V is 55(5)° and the calculated 2V is 51°. In transmitted light nestolaite is colourless. It does not show pleochroism but has strong pseudoabsorption caused by high birefringence. The chemical composition of nestolaite (wt.%, electronmicroprobe data) is: CaO 28.97, SeO2 61.14, H2O (calc.) 9.75, total 99.86. The empirical formula calculated on the basis of 4 O a.p.f.u. (atoms per formula unit) is Ca0.96Se1.02O3·H2O. The Raman spectrum is dominated by the Se–O stretching and O–Se–O bending vibrations of the pyramidal SeO3 groups and O–H stretching modes of the H2O molecules. The mineral is monoclinic, space group P21/c, with a = 7.6502(9), b = 6.7473(10), c = 7.9358(13) Å, β = 108.542 (12)°, V = 388.37(10) Å3 and Z = 4. The eight strongest powder X-ray diffraction lines are [dobs in Å(hkl) (Irel)]: 7.277 (100)(100), 4.949 (110)(37), 3.767 (002)(29), 3.630 (200)(58), 3.371 (020)(24), 3.163 (02)(74), 2.9783 (21)(74) and 2.7231 (112)(31). The crystal structure of nestolaite was determined by means of the Rietveld refinement from the powder data to Rwp = 0.019. Nestolaite possesses a layered structure consisting of CaΦ–SeO3 sheets, composed of edge-sharing polyhedra. Adjacent sheets are held by H bonds emanating from the single (H2O) group within the sheets. The nestolaite structure is topologically unique.

The Thermodynamics of Selenium Minerals in Near-Surface Environments

“…The mineral is very rare and occurs as light violet, round aggregations on sandstone associated with cobaltomenite, gypsum, orschallite, ferroselite, native selenium and others. Nestolaite was formed due to the supergene oxidation of primary Se minerals, such as native selenium and ferroselite [64].…”

Mineralogy and geochemistry of tellurium in the some mining sites of Transbaikalia

“…Due to the fact, that these same elements are also present in the tailings of tin-polymetallic and gold-bearing ores, the formation of hypergenic tellurium-bearing minerals is also possible in the geotechnogenic deposits formed in the tailings. Uranium minerals have long been known in the oxidation zone of the Sherlovogorsky deposit and are represented by monazite, metazinerite, uraninite, uranium-bearing tungstite and hydrotungstite [8], and with the exception of metazinerite have been studied very poorly. Nevertheless, U occurs in amounts exceeding hundredths of a percent at fairly intense migration (table 3).…”

Bernardevansite, Al2(Se4+O3)3⋅6H2O, dimorphous with alfredopetrovite and the Al-analogue of mandarinoite, from the El Dragón mine, Potosí, Bolivia

“…According to the Raman spectroscopic studies on hydrous materials containing (SeO 3 ) 2– (e.g. Wickleder et al , 2004; Frost et al , 2006; Frost and Keeffe, 2008; Djemel et al , 2013; Wolak et al , 2013; Kasatkin et al , 2014; Mills et al , 2014; Kampf et al , 2016b), we made the following tentative assignments of major Raman bands for bernardevansite. The broad bands between 2900 and 3500 cm –1 and those between 1500 and 1750 cm –1 are due to the O–H stretching and H–O–H bending modes in H 2 O groups, respectively.…”