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The new mineral nannoniite, Al2(OH)5F (Z=4), has been discovered in the Cetine di Cotorniano mine, Chiusdino, Siena, Tuscany, Italy. It occurs as spherical aggregates formed by micrometre-sized crystals, colourless to white in colour, with a white streak and a vitreous to earthy lustre. Fluorescence is bluish-yellow and yellowish-white under short- and longwave UV radiation, respectively. Electron microprobe analysis gave (in wt %) SO3 0.49, Al2O3 63.97, MgO 0.51, CaO 0.22, K2O 0.07, F 11.72, H2O(calc) 28.54, and - O = F -4.94 , with a total of 100.58. Nannoniite is monoclinic, with space group P21/n and with a=8.68 8(3), b=5.024 (2), c=9.734 (4) Å, β=90.77 (2)°, and V=424.9 (3) Å3. The crystal structure was solved using three-dimensional electron diffraction and refined to R(obs)=0.1524 for 2141 unique reflections with I>3σ(I). Nannoniite is homeotypic with gibbsite. In type material, nannoniite is associated with quartz, baryte, gypsum, and alunite in vugs of a silicified limestone. Its origin is probably related to the late-stage circulation of (Al,F)-rich fluids within the Sb ore deposit formerly exploited at the Cetine di Cotorniano mine. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Jeffbenite (having the same chemical composition of pyrope, ~ Mg3Al2Si3O12, and also known as TAPP phase) is a mineral inclusion only found in diamonds formed between about 300 and 1000 km depth) and is considered a stable phase in the transition zone (410–660 km depth) and/or in the shallowest regions of the lower mantle (around 660–700 km depth). This rare and enigmatic mineral is considered to be a pressure marker for super-deep diamonds and therefore it has a key role in super-deep diamond research. However, the pressure–temperature stability fields for Mg3Al2Si3O12 jeffbenite is unknown and its actual formation conditions remain unexplored. Here we have determined the thermodynamic pressure–temperature stability field for the jeffbenite Mg-end member and surprisingly discovered that it is stable at low pressure–temperature conditions, i.e., 2–4 GPa at 800 and 500 °C. Thus, Mg3Al2Si3O12 jeffbenite is not the high-pressure polymorph of pyrope and is likely a retrogressed phase formed during the late ascent stages of super-deep diamonds to the surface. [ABSTRACT FROM AUTHOR]

Thermal convection in the Earth's mantle is driven by lateral variations in temperature and density, which are substantially controlled by the local volume thermal expansion of the constituent mineral phases. Ringwoodite is a major component of the lower mantle transition zone, but its thermal expansivity and thermoelastic properties are still affected by large uncertainties. Ambient thermal expansion coefficient (αV0 ​​​​​​​), for instance, can vary as much as 100 % according to different experimental investigations available from the literature. In this work, we perform ab initio density functional theory calculations of vibrational properties of spinel-structured Mg 2 SiO 4 ringwoodite in order to provide reliable thermophysical data up to mantle transition zone conditions. Temperature- and pressure-dependent thermal expansivity has been obtained by phonon dispersion calculations in the framework of quasi-harmonic approximation (QHA) up to 25 GPa and 2000 K. Theoretical analysis of vibrational spectra reveals that accurate prediction of IR and silent modes, along with their relative mode Grüneisen parameters, is crucial to define thermal expansivity. A six-parameter analytical function is able to reproduce ab initio values fairly well in the whole investigated P – T range, i.e., αV(P,T)=(1.6033×10-5+8.839×10-9T+11.586×10-3T-1-6.055T-2+804.31T-3) ×exp⁡(-2.52×10-2P) , with temperature in kelvin and pressure in gigapascal. Ab initio static and isothermal bulk moduli have been derived for ringwoodite along with their P , T and cross derivatives, i.e., K0 = 184.3 GPa, KT,300K = 176.6 GPa, K0′ = 4.13, KT,300K′ = 4.16, ∂KT∂TP = - 0.0233 GPa K -1 and ∂2KT∂P∂T0=1.0×10-4 K -1. Computed thermal expansivity and thermoelastic properties support the evidence that QHA performs remarkably well for Mg 2 SiO 4 ringwoodite up to mantle transition zone temperatures. Since volume thermal expansion of ringwoodite is strongly pressure-dependent and its pressure dependence becomes more marked with the increasing temperature, internally consistent assessments and empirical extrapolation of thermoelastic data to deep mantle conditions should be taken with care to avoid inaccurate or spurious predictions in phase equilibrium and mantle convection numerical modeling. [ABSTRACT FROM AUTHOR]

The new mineral isselite, Cu6(SO4)(OH)10(H2O)4⋅H2O, has been discovered in the Lagoscuro mine, Monte Ramazzo mining complex, Genoa, Eastern Liguria, Italy. It occurs as sprays of blue acicular crystals, up to 0.1 mm long, associated with brochantite and posnjakite. Streak is light blue and the lustre is vitreous. Isselite is brittle, with irregular fracture and good cleavage on {001} and {100}. Measured density is 3.00(2) g/cm3. Isselite is optically biaxial (–), with α = 1.599(2), β = 1.633(2) and γ = 1.647(2) (determined in white light). The measured 2V is 63.6(5)°. Dispersion is moderate, with r > v. The optical orientation is X = b, Y = c and Z = a. Isselite is pleochroic, with X = light blue, Y = blue, Z = blue; X << Z < Y. Electron microprobe analyses give (wt.%): SO3 11.45(21), MgO 0.31(7), CoO 1.07(14), NiO 9.41(90), CuO 51.29(126), ZnO 1.10(20), H2Ocalc 24.21, total 98.84. The empirical formula of isselite, based on Σ(Mg,Co,Ni,Cu,Zn) = 6 atoms per formula unit, is (Cu4.80Ni0.94Co0.11Zn0.10Mg0.06)Σ6.00(S1.06O4.19)(OH)10⋅5H2O. Isselite is orthorhombic, space group Pmn21, with unit-cell parameters a = 6.8070(14), b = 5.8970(12), c = 20.653(4) Å, V = 829.0(3) Å3 and Z = 2. The crystal structure of isselite was refined from single-crystal X-ray diffraction data to R1 = 0.067 on the basis of 2964 reflections with Fo > 4σ(Fo). It shows a layered structure formed by zig-zag {001} layers of Cu-centred polyhedra. Sulfate groups occur in the interlayer along with one H2O group. Isselite is chemically related to redgillite and montetrisaite. [ABSTRACT FROM AUTHOR]

Thermodynamic and thermophysical properties of Na2SiO3 in the Cmc21 structural state are computed ab initio using the hybrid B3LYP density functional method. The static properties at the athermal limit are first evaluated through a symmetry-preserving relaxation procedure. The thermodynamic properties that depend on vibrational frequencies, viz., heat capacities, thermal expansion, thermal derivative of the bulk modulus, thermal correction to internal energy, enthalpy, and Gibbs free energy, are then computed in the framework of quasi-harmonic approximation. Acoustic branches are computed by solving the Christoffel determinant and are assumed to follow sine wave dispersion when traveling within the Brillouin zone. The procedure generates several thermo-physical properties of interest in materials science and geophysics (transverse and longitudinal wave velocities, shear modulus, Young modulus, Poisson ratio) all consistent with experimentally determined properties. A representative cluster is then abstracted from the cell and a detailed electron localization/delocalization analysis is performed on it, in the ground state geometry, and on deformed states imposed by two peculiar mixed asymmetric stretching/bending modes affecting the silicate chain that, according to literature data, have anomalous mode Grüneisen parameters. A Bader analysis reveals an intriguing feature associated with these deformations: an increase in the covalence of the Si-O bond that strengthens the linkage opposing the weakening induced by thermal stress. Finally, on the same cluster, the Ramsey contributions to the JNM coupling are evaluated by the gauge-independent atomic orbital method. The calculated isotropic chemical shifts of both 23Na and 29Si are again in substantial agreement with observations. [ABSTRACT FROM AUTHOR]

Using the hybrid B3LYP density functional method, we computed the ab initio thermodynamic and thermophysical properties of two sapphirine end-members, Mg4Al8Si2O20 (sapphirine-442) and Mg3Al10SiO20 (sapphirine-351), in the join Mg3(Mg1-XAlX)Al8(AlXSi1-X)SiO20 with X = 0-1. Static and vibrational calculations performed in the framework of the quasi-harmonic approximation allowed to define the equation of state (EOS), elastic constant tensor, seismic velocities, IR spectra, mode Grüneisen parameters, and thermodynamic properties of both sapphirine end-members. A modified Kieffer's model was adopted to evaluate the optic and acoustic mode contributions to thermodynamic functions stemming from ab initio phonon frequencies and directionally averaged seismic velocities, respectively. The extrinsic stability and liquidus phase relations of sapphirine were investigated in the model system MgO-Al2O3-SiO2 (MAS) at different pressure conditions by coupling first-principles calculations with the hybrid polymeric approach (HPA) for multicomponent liquids and minimizing the Gibbs free energy of liquid and solid phases through the convex-hull analysis of equipotential surfaces. According to our thermodynamic modeling, sapphirine turns out to have a small field of primary crystallization in the MAS ternary diagram at 1-bar pressure, which becomes larger due to pressure effects up to 10 kbar, then progressively shrinks and disappears above 21 kbar [ABSTRACT FROM AUTHOR]

Using the hybrid B3LYP density functional method, we computed the ab initio thermodynamic and thermophysical properties of two sapphirine end-members, Mg4Al8Si2O20 (sapphirine-442) and Mg3Al10SiO20 (sapphirine-351), in the join Mg3(Mg1-XAlX)Al8(AlXSi1-X)SiO20 with X = 0-1. Static and vibrational calculations performed in the framework of the quasi-harmonic approximation allowed to define the equation of state (EOS), elastic constant tensor, seismic velocities, IR spectra, mode Grüneisen parameters, and thermodynamic properties of both sapphirine end-members. A modified Kieffer's model was adopted to evaluate the optic and acoustic mode contributions to thermodynamic functions stemming from ab initio phonon frequencies and directionally averaged seismic velocities, respectively. The extrinsic stability and liquidus phase relations of sapphirine were investigated in the model system MgO-Al2O3-SiO2 (MAS) at different pressure conditions by coupling first-principles calculations with the hybrid polymeric approach (HPA) for multicomponent liquids and minimizing the Gibbs free energy of liquid and solid phases through the convex-hull analysis of equipotential surfaces. According to our thermodynamic modeling, sapphirine turns out to have a small field of primary crystallization in the MAS ternary diagram at 1-bar pressure, which becomes larger due to pressure effects up to 10 kbar, then progressively shrinks and disappears above 21 kbar [ABSTRACT FROM AUTHOR]