ALBERT

Description: Mambertiite, BiMo 5+ 2.80 O 8 (OH), is a new mineral identified in small vugs of quartz veins from Su Seinargiu, Sarroch, Cagliari, Sardinia, Italy. It occurs as pale yellow {001} tabular crystals, up to 1 mm in length and few mm thick, with adamantine lustre. Mambertiite is brittle, with a conchoidal fracture. It is associated with ferrimolybdite, muscovite, quartz, sardignaite, and wulfenite. Electron microprobe data (wt% – mean of 12 spot analyses) are: Mo 2 O 5 59.59, Bi 2 O 3 36.96, WO 3 2.03, H 2 O calc 1.48, sum 100.06. On the basis of 9 O atoms per formula unit, the empirical formula is Bi 0.99 (Mo 5+ 2.74 W 0.05 ) 2.79 O 7.97 (OH) 1.03 . Infrared spectra showed absorption bands consistent with the occurrence of OH – groups. Mambertiite is triclinic, space group $$P\overline{1}$$ , with a = 5.854(2), b = 9.050(3), c = 7.637(3) Å, α = 112.85(1), β = 102.58(1), = 90.04(1)°, V = 362.3(2) Å 3 , Z = 2. The crystal structure of mambertiite was solved and refined down to R 1 = 0.050 on the basis of 2019 observed [ F o 〉 4( F o )] reflections. It is composed by eight-fold coordinated Bi-centred polyhedra and five independent Mo-centred octahedra. Among the latter, two are completely occupied by molybdenum, whereas the remaining three are only partially occupied. Two kinds of ( $$10\overline{1}$$ ) layers occur in mambertiite, alternating along [ $$10\overline{1}$$ ]*: one is composed by Bi-centered polyhedra and the two partially occupied Mo4 and Mo5 sites, whereas the other is composed by the zigzag chains, running along c , formed by the fully occupied Mo1 and Mo2 sites, and the partially occupied Mo3 site. Mambertiite is structurally related to gelosaite, BiMo 6+ 2 O 7 (OH) · H 2 O; their relationships can be conveniently described through the OD theory. Mambertiite is the fourth known mineral with Bi and Mo as essential components. Its name honours the Italian mineral collector Marzio Mamberti (b. 1959) for his contribution to the knowledge of the Sardinian mineralogy. The mineral and its name have been approved by the IMA CNMNC (No. 2013–098).

Description: 〈span〉The new mineral sbacchiite (IMA 2017-097), Ca〈sub〉2〈/sub〉AlF〈sub〉7〈/sub〉, was found in a fossil fumarole (1944 eruption, 〈span〉T〈/span〉 ≈ 80 °C) at the rim of the crater of the Vesuvius volcano, Napoli, Italy, associated with gearsksutite, usovite, creedite and opal. It forms elongated crystals up to about 60 μm in length. On the basis of powder X-ray diffraction data and chemical analysis, the mineral was recognized to be identical to the corresponding synthetic phase. Crystals are transparent or translucent and colourless, with vitreous lustre and white streak. The tenacity is brittle. The measured density is 3.08(2) g/cm〈sup〉3〈/sup〉, the calculated density is 3.116 g/cm〈sup〉3〈/sup〉. The empirical formula, (based on 10 atoms per formula unit, 〈span〉apfu〈/span〉) is Ca〈sub〉2.02〈/sub〉Mg〈sub〉0.03〈/sub〉Al〈sub〉0〈/sub〉.〈sub〉99〈/sub〉F〈sub〉6.97〈/sub〉. Sbacchiite is orthorhombic, space group 〈span〉Pnma〈/span〉, with 〈span〉a〈/span〉 = 7.665(2), 〈span〉b〈/span〉 = 6.993(1), 〈span〉c〈/span〉 = 9.566(2) Å, 〈span〉V〈/span〉 = 512.2(2) Å〈sup〉3〈/sup〉 and 〈span〉Z〈/span〉 = 4. The eight strongest X-ray powder diffraction lines are [〈span〉d〈/span〉〈sub〉obs〈/sub〉 Å(〈span〉I〈/span〉)(〈span〉hkl〈/span〉)]: 3.840(45)(200), 3.563(85)(201), 3.499(100)(020), 2.899(55)(013), 2.750(30)(212), 2.281(20)(104), 2.255(52)(302) and 2.173(36)(131). The structure was refined to 〈span〉R〈/span〉 = 0.0479 for 457 reflections with 〈span〉I〈/span〉 〉 2σ(〈span〉I〈/span〉). The asymmetric unit contains one Al〈sup〉3+〈/sup〉 and two independent Ca〈sup〉2+〈/sup〉 cations and five fluorine anions. Aluminium is octahedrally coordinated by six fluorine atoms; the arrangement of F around the 7-coordinated Ca(1) conforms to a distorted pentagonal bipyramid and that around Ca(2) to a very distorted polyhedron (in 7 + 1 coordination). All the fluorine atoms are threefold coordinated. The structure framework shows “isolated” [AlF〈sub〉6〈/sub〉] octahedra, whereas the coordination polyhedra around Ca are linked by common edges [sequence: Ca(1)–Ca(2)–Ca(1)…] along [010] and the same holds for the connection along [001]. Along [100], however, only the pentagonal bipyramids around Ca(1) are connected by bridging corners.〈/span〉