Phase Transition of α-MgPO at High-Pressure and High-Temperature Conditions: The Third Polymorph of MgPO.

MgPO has two known polymorphs, i.e., α- and β-phase, at low and high temperatures, respectively.

Crystal structure of tetra-wickmanite, Mn(2+)Sn(4+)(OH)6.

The crystal structure of tetra-wickmanite, ideally Mn(2+)Sn(4+)(OH)6 [mangan-ese(II) tin(IV) hexa-hydroxide], has been determined based on single-crystal X-ray diffraction data collected from a natural sample from Långban, Sweden. Tetra-wickmanite belongs to the octa-hedral-framework group of hydroxide-perovskite minerals, described by the general formula BB'(OH)6 with a perovskite derivative structure. The structure differs from that of an ABO3 perovskite in that the A site is empty while each O atom is bonded to an H atom.

Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O.

Calcioferrite, ideally Ca4MgFe(3+) 4(PO4)6(OH)4·12H2O (tetra-calcium magnesium tetrairon(III) hexakis-phosphate tetra-hydroxide dodeca-hydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca4 AB 4(PO4)6(OH)4·12H2O, where A = Mg, Fe(2+), Mn(2+) and B = Al, Fe(3+). Calcioferrite and the other three known members of the group, montgomeryite (A = Mg, B = Al), kingsmountite (A = Fe(2+), B = Al), and zodacite (A = Mn(2+), B = Fe(3+)), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca3.

Redetermination of katayamalite, KLi3Ca7Ti2(SiO3)12(OH)2.

The crystal structure of katayamalite, ideally KLi3Ca7Ti2(SiO3)12(OH)2 (potassium trilithium hepta-calcium dititanium dodeca-silicate di-hydroxide), was previously reported in triclinic symmetry (C-1), with isotropic displacement parameters for all atoms and without the H-atom position [Kato & Murakami (1985 ▶). Mineral. J.

Penikisite, BaMg(2)Al(2)(PO(4))(3)(OH)(3), isostructural with bjarebyite.

The bjarebyite group of minerals, characterized by the general formula BaX(2)Y(2)(PO(4))(3)(OH)(3), with X = Mg, Fe(2+) or Mn(2+), and Y = Al or Fe(3+), includes five members: bjarebyite BaMn(2+) (2)Al(2)(PO(4))(3)(OH)(3), johntomaite BaFe(2+) (2)Fe(3+) (2)(PO(4))(3)(OH)(3), kulanite BaFe(2+) (2)Al(2)(PO(4))(3)(OH)(3), penikisite BaMg(2)Al(2)(PO(4))(3)(OH)(3), and perloffite BaMn(2+) (2)Fe(3+) (2)(PO(4))(3)(OH)(3). Thus far, the crystal structures of all minerals in the group, but penikisite, have been determined. The present study reports the first structure determination of penikisite (barium dimagnesium dialuminium triphosphate trihydroxide) using single-crystal X-ray diffraction data of a crystal from the type locality, Mayo Mining District, Yukon Territory, Canada.

Redetermination of clinobaryl-ite, BaBe(2)Si(2)O(7).

Clinobaryl-ite, ideally BaBe(2)Si(2)O(7) (chemical name barium diberyllium disilicate), is a sorosilicate mineral and dimorphic with baryl-ite. It belongs to a group of compounds characterized by the general formula BaM(2+) (2)Si(2)O(7), with M(2+) = Be, Mg, Fe, Mn, Zn, Co, or Cu, among which the Be-, Fe-, and Cu-members have been found in nature. The crystal structure of clinobaryl-ite has been re-examined in this study based on single-crystal X-ray diffraction data collected from a natural sample from the type locality (Khibiny Massif, Kola Peninsula, Russia).

Redetermination of junitoite, CaZn(2)Si(2)O(7)·H(2)O.

The crystal structure of the mineral junitoite, ideally CaZn(2)Si(2)O(7)·H(2)O (calcium dizinc disilicate monohydrate), was first determined by Hamilton & Finney [Mineral. Mag. (1985), 49, 91-95] based on the space group Ama2, yielding a reliability factor R of 0.

Nioboaeschynite-(Ce), Ce(NbTi)O(6).

Nioboaeschynite-(Ce), ideally Ce(NbTi)O(6) [cerium(III) niobium(V) titanium(IV) hexa-oxide; refined formula of the natural sample is Ca(0.25)Ce(0.79)(Nb(1.

High-pressure synthetic (Na(0.97)Mg(0.03))(Mg(0.43)Fe(0.17)Si(0.40))Si(2)O(6), with six-coordinated silicon, isostructural with P2/n omphacite.

The title compound, (sodium magnesium) [magnesium iron(III) silicon] disilicate, (Na(0.97)Mg(0.03))(Mg(0.

Redetermination of kovdorskite, Mg(2)PO(4)(OH)·3H(2)O.

The crystal structure of kovdorskite, ideally Mg(2)PO(4)(OH)·3H(2)O (dimagnesium phosphate hydroxide trihydrate), was reported previously with isotropic displacement paramaters only and without H-atom positions [Ovchinnikov et al. (1980 ▶). Dokl.

Lotharmeyerite, Ca(Zn,Mn)(2)(AsO(4))(2)(H(2)O,OH)(2).

Lotharmeyerite, calcium bis-(zinc/manganese) bis-(arsenate) bis-(hydroxide/hydrate), Ca(Zn,Mn(3+))(2)(AsO(4))(2)(H(2)O,OH)(2), is a member of the natrochalcite group of minerals, which are characterized by the general formula AM(2)(XO(4))(2)(H(2)O,OH)(2), where A may be occupied by Pb(2+), Ca(2+), Na(+), and Bi(3+), M by Fe(3+), Mn(3+), Cu(2+), Zn(2+), Co(2+), Ni(2+), Al(3+), and Mg(2+), and X by P(V), As(V), V(V), and S(VI). The minerals in the group display either monoclinic or triclinic symmetry, depending on the ordering of chemical components in the M site. Based on single-crystal X-ray diffraction data of a sample from the type locality, Mapimi, Durango, Mexico, this study presents the first structure determination of lotharmeyerite.

Pyrosmalite-(Fe), Fe(8)Si(6)O(15)(OH,Cl)(10).

Pyrosmalite-(Fe), ideally Fe(II) (8)Si(6)O(15)(OH,Cl)(10) [refined composition in this study: Fe(8)Si(6)O(15)(OH(0.814)Cl(0.186))(10)·0.

Lithio-marsturite, LiCa(2)Mn(2)Si(5)O(14)(OH).

Lithio-marsturite, ideally LiCa(2)Mn(2)Si(5)O(14)(OH), is a member of the pectolite-pyroxene series of pyroxenoids (hydro-pyroxenoids) and belongs to the rhodonite group. A previous structure determination of this mineral based on triclinic symmetry in space group P[Formula: see text] by Peacor et al. [Am.

Redetermination of despujolsite, Ca(3)Mn(SO(4))(2)(OH)(6)·3H(2)O.

The crystal structure of despujolsite [tricalcium manganese bis-(sulfate) hexahydroxide tri-hydrate], the Ca/Mn member of the fleischerite group, ideally Ca(3)Mn(4+)(SO(4))(2)(OH)(6)·3H(2)O, was previously determined based on X-ray diffraction intensity data from photographs, without H-atom positions located [Gaudefroy et al. (1968 ▶). Bull.

Kôzulite, an Mn-rich alkali amphibole.

The crystal structure of kôzulite, an Mn-rich alkali amphibole with the ideal formula NaNa(2)[Mn(4) (2+)(Fe(3+),Al)]Si(8)O(22)(OH)(2), tris-odium tetra-manganese iron/aluminium octa-silicate dihydroxide, was refined from a natural specimen with composition (K(0.20)Na(0.80))(Na(1.

Safflorite, (Co,Ni,Fe)As(2), isomorphous with marcasite.

Safflorite, a naturally occurring cobalt-nickel-iron diarsenide (Co,Ni,Fe)As(2), possesses the marcasite-type structure, with cations (M = Co + Ni + Fe) at site symmetry 2/m and As anions at m. The MAs(6) octa-hedra share two edges, forming chains parallel to c. The chemical formula for safflorite should be expressed as (Co,Ni,Fe)As(2), rather than the end-member format CoAs(2), as its structure stabilization requires the simultaneous inter-action of the electronic states of Co, Ni, and Fe with As(2) (2-) dianions.

Redetermination of olivenite from an untwinned single-crystal.

The crystal structure of olivenite, ideally Cu(2)(AsO(4))(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu(2)(As(0.92)P(0.08)O(4)), from Majuba Hill (Nevada, USA).

Redetermination of conichalcite, CaCu(AsO(4))(OH).

The crystal structure of conichalcite [calcium copper(II) arsenate(V) hydroxide], with ideal formula CaCu(AsO(4))(OH), was redetermined from a natural twinned specimen found in the Maria Catalina mine (Chile). In contrast to the previous refinement from photographic data [Qurashi & Barnes (1963 ▶). Can.

Iranite, CuPb10(CrO4)6(SiO4)2(OH)2, isomorphous with hemihedrite.

This study presents the first structural report of iranite, ideally CuPb10(CrO4)6(SiO4)2(OH)2 [copper decalead hexachromate bis(orthosilicate) dihydroxide], based on single-crystal X-ray diffraction data. Iranite is isomorphous with hemihedrite, with substitution of Cu for Zn and OH for F. The Cu atom is situated at the special position with site symmetry 1.

Kolbeckite, ScPO(4).2H(2)O, isomorphous with metavariscite.

This study presents the first structural report of kolbeckite, with the ideal formula ScPO(4).2H(2)O (scandium phosphate dihydrate), based on single-crystal X-ray diffraction data. Kolbeckite belongs to the metavariscite mineral group, in which each PO(4) tetrahedron shares four vertices with four ScO(4)(H(2)O)(2) octahedra and vice versa, forming a three-dimensional network of polyhedra.

Isokite, CaMg(PO(4))F(0.8)(OH)(0.2), isomorphous with titanite.

This study presents the first structural report of natural isokite (calcium magnesium phosphate fluoride), with the formula CaMg(PO(4))F(0.8)(OH)(0.2) (i.

Tyrrellite, Cu(Co0.68Ni0.32)2Se4, isostructural with spinel.

Tyrrellite, a naturally occurring Co-Ni-Cu selenide, has been studied by single-crystal X-ray diffraction. It possesses the normal spinel-type structure, with Cu occupying the tetrahedral site and (Co+Ni) the octahedral site. The average Cu-Se distance of 2.

Lattice dynamics of MgO at high pressure: theory and experiment.

The longitudinal acoustic and optical phonon branches along the Gamma-X direction of MgO at 35 GPa have been determined by inelastic x-ray scattering using synchrotron radiation and a diamond-anvil cell. The experimentally observed phonon branches are in remarkable agreement with ab initio lattice dynamics results. The derived thermodynamic properties, such as the specific heat CV and the entropy S are in very good accord with values obtained from a thermodynamically assessed data set involving measured data on molar volume, heat capacity at constant pressure, bulk modulus and thermal expansion.