Bassoite, SrV (sub 3) O (sub 7) .4H (sub 2) O; a new mineral from Molinello Mine, Val Graveglia, eastern Liguria, Italy

Bassoite, ideally SrV (sub 3) O (sub 7) .4H (sub 2) O, is a new mineral from the Molinello manganese mine, Val Graveglia, eastern Liguria, northern Apennines, Italy. It occurs as black euhedral to subhedral grains up to 400 mu m across, closely associated with rhodonite, quartz and braunite. Bassoite is opaque with a sub-metallic lustre and a black streak. It is brittle and neither fracture nor cleavage was observed; the Vickers micro-hardness (VHN (sub 100) ) is 150 kg/mm (super 2) (range 142-165; corresponding to a Mohs hardness of 4-4 1/2). The calculated density is 2.940 g/cm (super 3) (on the basis of the empirical formula and X-ray single-crystal data). Bassoite is weakly bireflectant and very weakly pleochroic from grey to a dark green. Internal reflections are absent. The mineral is anisotropic, without characteristic rotation tints. Reflectance percentages (R (sub min) and R (sub max) ) for the four standard COM wavelengths are 18.5%, 19.0% (471.1 nm); 17.2%, 17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and 16.2%, 16.8% (652.3 nm), respectively. Bassoite is monoclinic, space group P2 (sub 1) /m, with unit-cell parameters: a=5.313(3) Aa, b=10.495(3) Aa, c=8.568(4) Aa, beta =91.14(5) degrees , V=477.7(4) Aa (super 3) , a:b:c=0.506:1:0.816, and Z=2. The crystal structure was refined to R (sub 1) =0.0209 for 1148 reflections with F (sub o) >4sigma (F (sub o) ) and it consists of layers of VO (sub 5) pyramids (with vanadium in the tetravalent state) pointing up and down alternately with Sr between the layers (in nine-fold coordination). The nine most intense X-ray powder-diffraction lines [d in Aa (I/I (sub 0) ) (hkl)] are: 8.5663 (100) (001); 6.6363 (14) (011); 3.4399 (14) (121); 3.4049 (17) (121); 2.8339 (15) (122); 2.7949 (11) (122); 2.6550 (15) (200); 2.6237 (11) (040) and 1.8666 (15) (240). Electron microprobe analyses produce a chemical formula (Sr (sub 0.97) Ca (sub 0.02) Na (sub 0.01) )V (sub 3.00) O (sub 7) .4H (sub 2) O, on the basis of Sigma (Sr+Ca+Na)=1, taking the results of the structure refinement into account. The presence of water molecules was confirmed by micro-Raman spectroscopy. The name honours Riccardo Basso (b. 1947), full professor of Mineralogy and Crystallography at the University of Genova. The new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2011-028).