Fiemmeite Cu2(C2O4)(OH)2∙2H2O, a New Mineral from Val di Fiemme, Trentino, Italy

Abstract

Abstract:The new mineral species fiemmeite, Cu 2 (C 2 O 4 )(OH) 2 ·2H 2 O, was found NE of the Passo di San Lugano, Val di Fiemme, Carano, Trento, Italy (latitude 46.312 • N, longitude 11.406 • E). It occurs in coalified woods at the base of the Val Gardena Sandstone (upper Permian) which were permeated by mineralizing solutions containing Cu, U, As, Pb and Zn. The oxalate anions have originated from diagenesis of the plant remains included in sandstones. The mineral forms aggregate up to 1 mm across of sky blue platelets with single crystals reaching maximum dimensions of about 50 µm. Associated minerals are: baryte, olivenite, middlebackite, moolooite, brochantite, cuprite, devilline, malachite, azurite, zeunerite/metazeunerite, tennantite, chalcocite, galena. Fiemmeite is monoclinic, space group: P2 1 /c with a = 3.4245(6), b = 10.141(2), c = 19.397(3) Å, β = 90.71(1) • , V = 673.6(2) Å 3 , Z = 4. The calculated density is 2.802 g/cm 3 while the observed density is 2.78(1) g/cm 3 . The six strongest reflections in the X-ray powder diffraction pattern are: [d obs in Å (I)(hkl)] 5.079(100)(020), 3.072(58)(112), 9.71(55)(002), 4.501(50)(022), 7.02(28)(012), 2.686(25)(114). The crystal structure was refined from single-crystal data to a final R 1 = 0.0386 for 1942 observed reflections [I > 2σ(I)] with all the hydrogen atoms located from a Difference-Fourier map. The asymmetric unit contains two independent Cu 2+ cations that display a distorted square-bipyramidal (4+2) coordination, one oxalate anion, two hydroxyl anions and two water molecules. The coordination polyhedra of the two copper atoms share common edges to form polymeric rows running along [100] with composition [Cu 2 (C 2 O 4 )(OH) 2 ·2H 2 O] n . These rows are held together by a well-established pattern of hydrogen bonds between the oxalate oxygens not involved in the coordination to copper, the hydrogen atoms of the water molecules and the hydroxyl anions.

Biosorption of copper using nopal fibres: moolooite formation and magnesium role in the reactive crystallization mechanism

“…Moolooite is a copper oxalate mineral associated with malachite and with a structure poorly understood (Demartin et al 2018). The presence of malachite and moolooite Goldberg (1993) crystals were confirmed by XRD analysis and the main findings are explained in the next section.…”

X-ray diffraction study of middlebackite [CuII2C2O4(OH)2, di-copper oxalate dihydroxide], using a mineral specimen from Mooloo Downs Station, Western Australia and chemically synthesized material

“…In considering the results, caution should be exercised to note the possibility of the positional parameters being biased by correlation effects in the least squares calculations. Table VII provides a comparative analysis of the bond lengths and angles for the three middlebackite studies and makes comparisons with the recently published structure of the related dihydrate, fiemmeite, Cu 2 (C 2 O 4 )(OH) 2 •2H 2 O (Demartin et al, 2018). The table includes representative weighted average (WA) values for key distances and angles according to the inverse variances.…”

Editorial for Special Issue “New Mineral Species and Their Crystal Structures”

“…It occurs in coalified woods which were permeated by mineralizing solutions containing Cu, U, As, Pb and Zn. The oxalate anions have originated from altered plant remnants included in sandstone [17]. Biagioni with co-authors studied Si-analogue of chalcophyllite from the Cretaio Prospect in Grosseto, which was named tiberiobardiite in the honour of Tiberio Bardi, a mineral collector who found a specimen which became the holotype of tiberiobardiite with the simplified formula Cu 9 Al(SiO 3 OH) 2 (OH) 12 (H 2 O) 6 (SO 4 ) 1.5 •10H 2 O [18].…”