Original paper

Piemontite-(Pb), CaPbAl2Mn3+[Si2O7][SiO4]O(OH), a new mineral species of the epidote supergroup

Chukanov, Nikita V.; Varlamov, Dmitry A.; Nestola, Fabrizio; Belakovskiy, Dmitry I.; Goettlicher, Jörg; Britvin, Sergey N.; Lanza, Arianna; Jancev, Simeon

Abstract

The new epidote-supergroup mineral piemontite-(Pb), the Pb-dominant analogue of piemontite, was discovered in the "Mixed Series" formation, near Nežilovo village, Jacupica Mountains, Macedonia. Associated minerals are barite, dolomite, calcite, hematite, Zn- and Mn-bearing phlogopite, hedyphane, nežilovite, rinmanite, gahnite and braunite. Piemontite-(Pb) forms purplish-red imperfect crystals up to 0.5 mm × 2 mm in size and occurs also in random aggregates. Dcalc is 4.282 g/cm3. It is biaxial (−), α = 1.835(10), β = 1.885(10), γ = 1.895(10), 2 V (meas.) = 30-40°, 2 V (calc.) = 47°. The IR spectrum is given. The chemical composition is (electron microprobe, mean of 32 analyses, wt.%): CaO 11.86, PbO 26.34, Al2O3 14.04, Mn2O3 8.61, Fe2O3 8.75, SiO2 28.90; H2O (calculated from structural data) 1.47; total 99.97. The empirical formula based on 13 O atoms, taking into account structural data, is: Ca(Pb0.73Ca0.30)(Al0.65Fe3+0.34)Al(Mn3+0.67Fe3+0.33)(Si2.96Al0.04)O12(OH).The trivalent state of Mn was con firmed by Mn K-edge XANES spectroscopy. The crystal structure was solved using singlecrystal X-ray diffraction data. Piemontite-(Pb) is monoclinic, space group P21/m; a = 8.938(1), b = 5.6810(6), c = 10.289(1) Å, β = 114.17(1)°, V = 476.66(9) Å3, Z = 2. The strongest lines of the powder diffraction pattern [d, Å (I, %) (hkl)] are: 8.12 (68) (100), 4.67 (53) (110, 11-1), 3.518 (77) (21-1), 2.931 (100) (11-3, 30-2, 020), 2.843 (51) (211), 2.736 (57) (013), 2.610 (66) (31-1). Type material is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 4193/1.

Keywords

piemontite-(pb)new mineralepidote supergroupcrystal structurenezilovomacedonia