As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: IV. Lombardoite, Ba2Mn3+(AsO4)(2)(OH) and aldomarinoite, Sr2Mn3+(AsO4)(2)(OH), description and crystal structure

Lombardoite, ideally Ba2Mn3+(AsO4)(2)(OH), and aldomarinoite, ideally Sr2Mn3+(AsO4)(2)(OH), are two new minerals of the arsenbracke-buschite group in the brackebuschite supergroup, discovered in Fe-Mn ore in metaquartzites of the abandoned mine of Valletta, Canosio, Val Maira, Cuneo Province, Piedmont, Italy. They occur as red-brown and orange brown, respectively, as subhedral crystals (< 0.5 mm) in thin masses, associated with quartz, aegirine, baryte, calcite, hematite, muscovite and Mn minerals such as cryptomelane, braunite and manganberzeliite. Both minerals are translucent, have yellow-orange streak and vitreous lustre. Both are brittle. Estimated Mohs hardness is 6-61/2 for lombardoite (by analogy to canosioite), and 41/2-5 for aldomarinoite (by analogy to tokyoite). Calculated densities are 5.124 g/cm(3) for lombardoite and 4.679 g/cm(3) for aldomarinoite. Both minerals are biaxial (+). Lombardoite shows 2V(z)(meas.) = 78(4)degrees and is pleochroic with X= yellowish brown, Y= brown and Z= reddish brown (Z > Y > X). Aldomarinoite has 2V(z)(meas.)= 67.1(1)degrees, and is pleochroic with X= brown, Y = brownish orange and Z= yellowish brown (Z> Y > X). Point analyses by electron microprobe using wavelength dispersive spectroscopy resulted in the empirical formula (based on 9 0 anions): (Ba1.96Sr0.17Pb0.04Na0.02Ca0.02)(Sigma 2.21)(Mn-0.062(3+) Fe0.133+Al0.06,Mg-0.11)(Sigma 0.92)[(As0.87V0.12P0.01)(Sigma 1.00)O-4](2)(OH) for lombardoite, and (Sr1.93Ca0.21 Ba0.04Pb0.01)Sigma(2.19)(Mn0.483+Al0.35Fe0.213+Mg0.01)(Sigma 1.05)[(As0.92V0.03)Sigma O-0.95(4)(OH) for aldomarinoite. The absence of H 2 O was confirmed by Raman spectroscopy and infrared spectroscopy. Both minerals are monoclinic, P2(1)/m, with unit-cell parameters a = 7.8636(1) angstrom, b = 6.13418(1) angstrom, c = 9.1197(1) angstrom, beta= 112.660(2)degrees and V= 405.94(1)angstrom(3), for lombardoite and a= 7.5577(4) angstrom, b = 5.9978(3) angstrom, 8.7387(4) angstrom, beta =111.938(6)degrees and V= 367.43(3) angstrom(3), for aldomarinoite. The eight strongest powder X-ray diffraction lines are [d, angstrom (I-rel) (hkl)]: 6.985 (39) (10 (1) over bar), 3.727 (33) (111), 3.314 (100) (21 (1) over bar), 3.073 (24) (020), 3.036 (33) (21 (2) over bar, 10 (3) over bar), 2.810 (87) (12 (1) over bar, 112), 2.125 (20) (301, 11 (4) over bar) and 1.748 (24) (321) for lombardoite and 3.191 (89) (21 (1) over bar), 2.997 (45) (020), 2.914 (47) (21 (2) over bar, 10 (3) over bar), 2.715 (100) (112), 2.087 (39) (12 (3) over bar, 1.833 (32) (31 (4) over bar), 1.689 (36) (321), 1.664 (21) (132) for aldomarinoite. The minerals are isostructural with brack-ebuschite: infinite chains of edge sharing octahedra running parallel to the b axis and decorated with AsO4 groups are connected along the a and c axes through Ba and Sr atoms in lombardoite and aldomarinoite, respectively. The minerals are named after Bruno Lombardo (1944-2014), geologist and petrologist at C.N.R. (National Research Council of Italy), and Aldo Marino (b. 1942) the mineral collector and founding member of the AMI - Italian Micromineralogical Association.