Cortesognoite, CaV2Si2O7(OH)2·H2O, a New Mineral from the Molinello Manganese Mine, Graveglia Valley, Italy

Abstract

Cortesognoite (IMA 2014-029), CaV2Si2O7(OH)2·H2O, is a new vanadium silicate mineral that occurs within V-bearing lawsonite in association with vanadiocarpholite, chalcocite, quartz, minor poppiite, roscoelite, vanadomalayaite and volborthite in a silicified wood hosted in Mn-ore-bearing metacherts from the Molinello manganese mine in the Graveglia Valley, Northern Apennines, Liguria, Italy. The mean chemical composition of type cortesognoite by electron probe microanalysis is (wt%) SiO2 34.33, V2O3 31.38, CaO 15.80, Al2O3 7.69, MnO 0.14, FeO 0.09, MgO 0.06, TiO2 0.02 and H2O 10.29, totaling 99.80, giving rise to an empirical formula of (Ca0.99Mn0.01)(V1.47Al0.53Mg0.01)Si2.00O7(OH)2·H2O. The end-member formula is CaV2Si2O7(OH)2·H2O. Cortesognoite has the Cmcm lawsonite structure with a = 5.85(1) Å, b = 8.79(1) Å, c = 13.13(1) Å, V = 675(1) Å3 and Z = 4 as revealed by electron back-scatter diffraction. The calculated density using the measured composition is 3.44 g/cm3. Cortesognoite is a secondary alteration phase, formed with V-bearing lawsonite by multi-stage hydrothermal processes that occurred in the silicified fossil wood. The mineral name is in honor of Luciano Cortesogno, professor of petrography at University of Genova, Italy.