Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure

High pressure structural distortions of the hexagonal close packed (hcp) element zinc have been a subject of controversy. Earlier experimental results and theory showed a large anomaly in lattice strain with compression in zinc at about 10 GPa which was explained theoretically by a change in Fermi surface topology. Later hydrostatic experiments showed no such anomaly, resulting in a discrepancy between theory and experiment. We have computed the compression and lattice strain of hcp zinc over a wide range of compressions using the linearized augmented plane wave (LAPW) method paying special attention to k-point convergence. We find that the behavior of the lattice strain is strongly dependent on k-point sampling, and with large k-point sets the previously computed anomaly in lattice parameters under compression disappears, in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press

Thermodynamics of pyrope-majorite, Mg3Al2Si3O12-Mg4Si4O12, solid solution from atomistic model calculations

Static lattice energy calculations, based on empirical pair potentials have been performed for a large set of different structures with compositions between pyrope and majorite, and with different states of order of octahedral cations. The energies have been cluster expanded using pair and quaternary terms. The derived ordering constants have been used to constrain Monte Carlo simulations of temperature-dependent properties in the ranges of 1073 3673K and 0 20 GPa. The free energies of mixing have been calculated using the method of thermodynamic integration. At zero pressure the cubic/tetragonal transition is predicted for pure majorite at 3300 K. The transition temperature decreases with the increase of the pyrope mole fraction. A miscibility gap associated with the transition starts to develop at about 2000K and xmaj 0.8, and widens with the decrease in temperature and the increase in pressure. Activity composition relations in the range of 0 20 GPa and 1073 2673K are described with the help of a high-order Redlich Kister polynomial

Ferrofettelite, [Ag6As2S7][Ag10FeAs2S8], a new sulfosalt from the Glasberg quarry, Odenwald, Germany

Ferrofettelite, ideally [Ag6As2S7][Ag10FeAs2S8], is a new mineral (IMA No. 2021-094) from the Glasberg quarry, Nieder-Beerbach, Odenwald, south-western Germany. It occurs as anhedral to subhedral flakes and grains up to 80 μm, associated with proustite and xanthoconite, on arsenolite, calcite and prehnite. Ferrofettelite is opaque with a metallic luster and possesses a dark reddish-grey streak. It is brittle with an uneven fracture; the Vickers microhardness (VHN20) is 122 kg/mm2(range 111–131). The calculated density is 5.74 g/cm3(on the basis of the empirical formula). In plane-polarized reflected light, ferrofettelite is greyish white. Between crossed polars it is weakly anisotropic with red internal reflections. Electron-microprobe analyses give the chemical formula Ag16.04(Fe0.55Hg0.40Cu0.02)Σ0.97(As3.94Sb0.03)Σ3.97S15.02 on the basis of total atoms = 36. Ferrofettelite is monoclinic, space group C2, with a = 26.011(2), b = 15.048(1), c = 15.513(1) Å, β = 90.40(1)°, V = 6071.9(7) Å3, and Z = 8. The six strongest Bragg peaks in the X-ray powder diffraction pattern (d[Å], I[%], hkl) are: (3.18, 50, -801), (3.104, 100, 005), (3.004, 60, -802), (2.755, 40, -443), (2.501, 30, -444) and (1.880, 30, 1240). The crystal structure can be described as the alternation of two kinds of layers along the c-axis: layer A with general composition [Ag6As2S7]2-and layer B with a general composition of [Ag10FeAs2S8]2+. In the structure, the Ag atoms adopt various coordinations extending from quasi linear to quasi tetrahedral, the AsS3 groups form pyramids as are typically observed in sulfosalts, and mixed (Fe,Hg) links two sulfur atoms in a linear coordination. Ferrofettelite is the first reported inorganic phase showing a linear coordination for Fe2+. The high-temperature behavior of ferrofettelite was studied up to 410 K and compared to that of fettelite. © 2022 Cambridge University Press. All rights reserved.12 month embargo; published online: 25 March 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Loomisite, Ba[Be2P2O8]•H2O, the first natural example with the zeolite ABW-type framework, from Keystone, Pennington County, South Dakota, USA

A new beryllophosphate mineral species, loomisite (IMA 2022-003), ideally Ba[Be2P2O8]•H2O, was found from the Big Chief mine near Keystone, Pennington County, South Dakota, USA. It occurs as divergent sprays of very thin bladed crystals with a tapered termination. Individual crystals are found up to 0.80 x 0.06 x 0.03 mm. Associated minerals include dondoellite, earlshannonite, mitridatite, rockbridgeite, jahnsite-(CaMnFe), and quartz. No twinning or parting is observed macroscopically. Loomisite is murky white in transmitted light, transparent with white streak and silky to vitreous luster. It is brittle and has a Mohs hardness of 3½-4, with perfect cleavage on (100) and (-110). The measured and calculated densities are 3.46(5) and 3.512 g/cm3, respectively. Optically, loomisite is biaxial (+), with α = 1.579(5), β = 1.591(5), γ = 1.606(5) (white light), 2V (meas.) = 82(2)º, 2V (calc.) = 85º. It is non-pleochroic under polarized light, with a very weak (r > v) dispersion. The mineral is insoluble in water or hydrochloric acid. An electron microprobe analysis, along with the BeO content measured with an ICP-MS, yields an empirical formula (based on 9 O apfu) (Ba0.96Ca0.06)Ʃ1.02[(Be1.96Fe0.06)Ʃ2.02P1.99O8]•H2O, which can be simplified to (Ba,Ca)[(Be,Fe)2P2O8]•H2O. Loomisite is monoclinic, with space group Pn and unit-cell parameters a = 7.6292(18), b = 9.429(2), c = 4.7621(11) Å, β = 91.272(5)◦, V= 342.47(14) Å3, and Z = 2. Its crystal structure is characterized by a framework of corner-sharing PO4 and BeO4 tetrahedra. The framework can be considered as built from the stacking of sheets consisting of 4- and 8-membered rings (4.82 nets) along [001] or hexagonal layers (63 nets) along [010]. The extra-framework Ba2+ and H2O are situated in the channels formed by the 8-membered rings. Topologically, loomisite represents the first natural example with the zeolite ABW-type framework, which is adopted by over 100 synthetic compounds with different chemical compositions. © 2022 Cambridge University Press. All rights reserved.12 month embargo; published online: 20 October 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Guangyuanite, Pb3Cl3(Se4+O3)(OH), a new lead chloride selenite mineral from the El Dragón mine, Potosí, Bolivia

A new mineral species, guangyuanite, ideally Pb3Cl3(Se4+O3)(OH), was discovered from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. It occurs as equant crystals. Associated minerals are Co-bearing krut'aite-penroseite, chalcomenite, schmiederite, olsacherite, phosgenite, anglesite, cerussite, and franksousaite. Guangyuanite is pale yellow-brown in transmitted light, transparent with white streak and vitreous luster. It is brittle and has a Mohs hardness of ∼3. No parting or cleavage was observed. The calculated density is 7.63 g/cm3. An electron microprobe analysis yielded an empirical formula [based on 7 (O + Cl) apfu] Pb3.02Cl3.01(Se4++0.99O3)(OH), which can be simplified to Pb3Cl3(Se+4O3)(OH). Guangyuanite is isostructural with synthetic Pb3Br3(Se4+O3)(OH). It is orthorhombic, with space group Pnma and unit-cell parameters a = 11.0003(5), b = 10.6460(5), c = 7.7902 A, V = 912.31(6) A3, and Z = 4. The crystal structure of guangyuanite contains two symmetrically-distinct Pb (Pb1 and Pb2) cations, with Pb1 coordinated by eight anions (4O + 4Cl) and Pb2 only by six anions (3O + 3Cl), forming a marked lopsided coordination typical of Pb2+with a stereochemically-Active 6s2lone-electron-pair. The Se4+cation forms a typical [Se4+O3] trigonal pyramid. The crystal structure of guangyuanite can be described as consisting of layers of edge-sharing [Pb1O4Cl4] polyhedra parallel to (100). These layers are linked together by sharing polyhedral corners (Cl atoms), as well as [Pb2O3Cl3] and [Se4+O3] groups. Chemically, guangyuanite is one of six lead-chloride-selenite minerals reported thus far and closely related to orlandiite Pb3Cl4(Se4+O3) H2O. © 2023 Cambridge University Press. All rights reserved.12 month embargo; first published 07 December 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Marshallsussmanite, NaCaMnSi 3 O 8 (OH), a new pectolite-group mineral providing insight into hydrogen bonding in pyroxenoids

Marshallsussmanite (IMA2013-067) is a new pyroxenoid mineral from the Wessels mine, Kalahari Manganese Field, Northern Cape Province, South Africa. Marshallsussmanite has ideal formula NaCaMnSi3O8(OH) and triclinic P symmetry. Marshallsussmanite forms vitreous pink bladed crystals to 2.1 cm. The mineral shows perfect cleavage on both {100} and {001}. The chemical composition from electron microprobe (average of 20 analyses) and inductively coupled plasma mass spectrometer analysis (average of three analyses) is Li2O 0.43, Na2O 8.06, MgO 0.08, CaO 15.33, MnO 21.79, SiO2 51.71; totalling 97.40 wt.%. The empirical formula, normalized to 3 Si and assuming 1 H apfu is Li0.100Na0.906Ca0.953Mg0.007Mn1.071Si3O8(OH). Unit-cell parameters from single crystal X-ray diffraction are a = 7.7854(4), b = 6.9374(4), c = 6.8516(3) Å, α = 90.683(3)°, β = 94.330(3)°, γ = 102.856(3)°, V = 359.59(3) Å3; Z = 2. The crystal structure refinement converged with Robs = 0.0248 and site occupancy refinement gives crystal chemistry [Na0.948Li0.052][Ca0.793Mn0.207] [Mn0.937Ca0.063]Si3O8(OH). Marshallsussmanite is a single chain silicate with a repeat interval of three tetrahedra (i.e. dreier chain). Marshallsussmanite is a member of the pectolite group of pyroxenoids, which also includes barrydawsonite-(Y), cascandite, pectolite, serandite and tanohataite. Parallel silicate chains form layers, intercalated with well-ordered cation layers. Calcium and Mn both exhibit octahedral coordination, while Na has four bonded interactions in a coordination sphere (radius 3 Å) of seven separate O atoms. Procrystal electron density and bond valence modelling results are compared. The mineral has an unusually strong hydrogen bond with O4O3 separation of 2.458(2) Å. Unlike pectolite and serandite, O4 in marshallsussmanite acts as an H-bond donor and O3 is an H-bond acceptor. Cation ordering in pyroxenoids has a substantial impact on the H position and corresponding H-bonding schemata. Copyright © The Author(s), 2018. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland.12 month embargo; published online: 21 February 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]