Crystal Chemical Formula Research Articles

Investigations on FCAM-III (Ca2.38Mg2.09Fe3+10.61Fe2+1.59Al9.33O36): A new homologue of the aenigmatite structure-type in the system CaO-MgO-Fe2O3-Al2O3

In the course of a systematic study of a part of the quaternary system Fe2O3-CaO-Al2O3-MgO (FCAM) the previously unknown compound Ca2.38Mg2.09Fe3+10.61Fe2+1.59Al9.33O36 (FCAM-III) has been synthesized. By analogy with the so-called SFCA series [1–5], our investigation in the system of FCAM shows the existence of a stoichiometric homologous series M14+6nO20+8n, where M = Fe, Ca, Al, Mg and n = 1 or 2.In air, we can prove the formation of coexisting FCAM-III and FCAM-I solid solutions at 1400°C. By increasing the temperature up to 1425°C FCAM-I disappears completely and FCAM-III co-exists with magnesiumferrite and a variety of calcium iron oxides. At 1450°C FCAM-III breaks down to a mixture of FCAM-I again as well as magnesioferrite and melt. Small single-crystals of FCAM-III up to 35µm in size could be retrieved from the 1425°C experiment and were subsequently characterized using electron microprobe analysis and synchroton X-ray single-crystal diffraction. Finally the Fe2+/Fetot ratio was calculated from the total iron content based on the crystal-chemical formula obtained from EMPA measurements and charge balance considerations. FCAM-III or Ca2.38Mg2.09Fe3+10.61Fe2+1.59Al9.33O36 has a triclinic crystal structure (space group P1̅). The basic crystallographic data are: a = 10.223(22) Å, b = 10.316(21) Å, c = 14.203(15) Å, α = 93.473(50)°, β = 107.418(67)°, γ = 109.646(60)°, V = 1323.85(2) ų, Z = 1.Using Schreinemaker's technique to analyze the phase relations in the system Fe2O3-CaO-Al2O3-MgO it was possible to obtain the semi-quantitative stability relations between the participating phases and construct a topologically correct phase sequence as a function of T and fO2. The analysis shows that Ca2Al0.5Fe1.5O5 (C2A0.25F0.75) and CaAl1.5Fe2.5O7 (CA0.75F1.25) with higher calculated Fe2+ contents are preferably formed at lower oxygen fugacity and react to CaAl0.5Fe1.5O4 (CA0.25F0.75) by increasing fO2. Spinel-type magnesium-aluminium-ferrite (Mg,Fe2+)Fe3+1.25Al0.75O4 or (MA0.375F0.625) is the typical phase which occurs at high temperature (1400°C).

New data on betekhtinite: Refinement of crystal structure and revision of chemical formula

The crystal structure of betekhtinite from Dzhezkazgan copper ore deposit, Kazakhstan, has been refined to R1 = 0.047 for 1321 unique observed reflections. The mineral is orthorhombic, Immm, a = 3.9047(6), b = 14.796(2), c = 22.731(3) Å, and V = 1313.3(3) Å3. Structure refinement revealed five additional partially occupied Cu sites compared to the previous structural study. The structure contains one Pb and thirteen Cu sites. The coordination of the Pb site is sevenfold. Coordination geometries of the Cu sites are variable: The Cu1, Cu2, Cu3 Cu6, Cu7, Cu8, and Cu9 sites are tetrahedrally coordinated, whereas Cu4, Cu5, Cu10, Cu11, and Cu13 have a triangular coordination. The Cu12 site is coordinated by two S atoms to form a CuS2 dumbell. The crystal structure of betekhtinite is based upon complex Pb-Cu sulfide rods running parallel to the a axis. The rods have a rhombus-like cross sections with lateral dimensions of ca. 11 x 16 Å2. The core of the rod is composed from the CuS4 tetrahedra and may be considered a module extracted from the archetype structure of fluorite, CaF2. The tetrahedral columns are further incrustated by the Cu4S3 and Cu5S3 triangles and Pb atoms to form the [Pb2Cu16S15] rods, which are linked to each other along the b axis via S6 atoms. The low-occupied Cu sites are located in between the rods. The structural formula determined on the basis of the crystal-structure refinement can be written as Pb2Cu22.18Fe1.04S15, which is in good agreement with the chemical analyses of betekhtinite and disagrees notably with the formula Pb2(Cu,Fe)21S15 suggested by Dornberger-Schiff and Höhne. The general crystal chemical formula of betekhtinite can be written as Pb2(Cu,Fe)22-24S15. Information-based structural complexity parameters for betekhtinite are: Ig = 3.696 bits/atom and IG,total = 144.131 bits/cell. Decomposition of betekhtinite into a mixture of galena (PbS; Ig = 1.000 bits/atom; IG,total = 2.000 bits/cell) and chalcocite (Cu2S; IG = 1.500 bits/atom; IG,total = 12.000 bits/cell) at temperatures above 150 °C is associated with the loss of structural complexity and the rise of configurational entropy of the system.

Gurimite, Ba3(VO4)2 and hexacelsian, BaAl2Si2O8 – two new minerals from schorlomite-rich paralava of the Hatrurim Complex, Negev Desert, Israel

AbstractTwo new barium-bearing minerals: gurimite, Ba3(VO4)2 (IMA2013-032) and hexacelsian, BaAl2Si2O8 (IMA2015-045) were discovered in veins of paralava cutting gehlenite-flamite hornfels located in the Gurim Anticline in the Negev Desert, Israel. Gurimite and hexacelsian occur in oval polymineralic inclusions in paralava and are associated with gehlenite, pseudowollastonite or wollastonite, rankinite, flamite, larnite, schorlomite, andradite, fluorapatite, fluorellestadite, kalsilite, cuspidine, aradite, zadovite and khesinite. Gurimite and hexacelsian form elongate crystals <10 μm thick. The minerals are colourless and transparent with a white streak and vitreous lustre, and have (0001) cleavage, respectively good in gurimite and very good in hexacelsian. Fracture is irregular. Density calculated using empirical formulas gave 5.044 g cm–3 for gurimite and 3.305 g cm–3 for hexacelsian. Mean refractive indexes, 1.945 and 1.561, respectively, were also calculated using the empirical formulas and the Gladstone-Dale relationship. The minerals are uniaxial and nonpleochroic. The following empirical crystal chemical formulae were assigned to holotype gurimite: (Ba2.794K0.092Ca0.084Na0.033Sr0.017)∑3.020(V1.8275+S0.0916+P0.0515+Al0.040Si0.005Fe0.0053+)∑2.017O8,and holotype hexacelsian: (Ba0.911K0.059Ca0.042Na0.010)∑1.022Al1.891Fe0.0723+Si2.034O8. The Raman spectrum of hexacelsian is similar to the one of the synthetic disordered β-BaAl2Si2O8. The Raman spectrum of gurimite is identical to that of synthetic Ba3(VO4)2. The electron back-scattered diffraction (EBSD) pattern of gurimite was fitted to the structure of its synthetic analogue with the cell parameters of R3m, a = 5.784(1),c = 21.132(1) Å, V = 612.2(2) Å3, Z = 3, giving a mean angular deviation = 0.43° (good fit). The Raman spectra of hexacelsian and its EBSD pattern suggest that natural hexacelsian corresponds to disordered synthetic β-hexacelsian P63/mcm, a = 5.2920(4) Å, c = 15.557(2) Å, α = β = 90°, γ = 120°. We suggest that after relatively fast crystallization of the main constituents of the paralava, gurimite, hexacelsian and also other Ba-bearing phases crystallized from residual melt enriched in incompatible elements that filled interstices between crystals of the main constituents.

New insights into the crystal chemistry of agardite-(Ce): refinement of the crystal structure, hydrogen bonding, and epitaxial intergrowths with the Sb-analogue of auriacusite

Agardite-(Ce) from Clara Mine, Schwarzwald, Germany, has been investigated by means of electron microprobe analysis, single-crystal X-ray analysis, XANES spectroscopy and IR spectroscopy. Hexagonal unit-cell parameters are: a = 13.598(6), c = 5.954(3) A; V = 953.5(2) A3; space group P63/m. The structure has been solved and refined to final R 1 = 3.87%, wR 2 = 5.02 for 786 I > 3σ(I). Hydrogen atoms have been localized. The crystal-chemical formula is (Z = 2): A(1)(Ce0.82Ca0.14Sr0.04)Σ1.00 A(2)(Ca0.03Ce0.02)Σ0.05 [Cu5.75(Fe3+, Mn)0.20]Σ5.95 [ T(1)(AsO4) 2.96 (2) (SbO4)0.04)]Σ3.00 (OH)5.96O0.04·3H2O. Hydrogen bonding in agardite-series minerals has been characterized for the first time. IR spectra of agardite-(Ce) and agardite-(Nd) from Lavrion used for comparison, as well as structural data indicate the presence of isolated H+ cations that do not form strong covalent bonds with coordinating O atoms. Agardite-(Ce) from Clara Mine forms epitaxial growths with the Sb-analogue of auriacusite. The latter mineral was characterized by EDS analyses; its typical empirical formulae are $${\text{Ca}}_{0.0 6} {\text{Ce}}_{0.0 4} {\text{Fe}}^{ 3+ }{}_{ 1.0 6} {\text{Cu}}_{0. 8 9}$$ [(SbO4)0.58(AsO4)0.38(SiO4)0.04]Σ1.00(O,OH) and $${\text{Ca}}_{0.0 7 5} {\text{Ce}}_{0.0 4} {\text{Fe}}^{ 3+ }{}_{0. 9 3} {\text{Cu}}_{0. 9 7}$$ [(SbO4)0.59(AsO4)0.35(SiO4)0.06]Σ1.00(O,OH). The formation of uniaxial growths of the Sb-analogue of auriacusite and agardite-(Ce) is caused by the close values of their c parameters (for auriacusite s.s. c = 5.9501(5) A). Three-valence state of iron and five-valence of antimony in both minerals has been validated by means of Fe K- and Sb L 2,3-edge XANES spectroscopy.

The first layer potassium–bismuth-nickel oxophosphate KBi4Ni2(PO4)3O4: Synthesis, crystal structure, and expected magnetic properties

The new potassium–bismuth–nickel oxophosphate obtained by hydrothermal synthesis in the Bi(OH)3–NiCO3–K2CO3–K3PO4 system is studied by X-ray diffraction, IR spectroscopy, and Raman spectroscopy. Parameters of the orthorhombic cell are as follows: a = 13.632(1) A, b = 19.610(2) A, and c = 5.4377(3) A; V = 1452.64(2) A3; and space group Pnma. The structure is solved and refined to the final discrepancy factor R 1 = 5.76% in the anisotropic approximation of atomic displacements using 3606 reflections with I > 2σ(I). The crystal-chemical formula (Z = 4) is KBi4{Ni2O4(PO4)3}, where the composition of the layer nickel–phosphate polyanion is enclosed in braces. Theoretical calculations show that all exchange spin interactions between Ni2+ ions are antiferromagnetic and very weak (J < 0.1 cm–1) because of the polyatomic character of bridging Ni–O–P–O–Ni and Ni–O–Bi–O–Ni groups. Thus, this compound is expected to be paramagnetic with very weak antiferromagnetic exchange interactions and appreciable energy of zero-field splitting of the spin levels of Ni2+ ions.

New Mineral Names*,†

This New Mineral Names has entries for 10 new minerals, including bulgakite, dyrnaesite-(La), eleonorite, gatewayite, joanneumite, mendeleevite-(Nd), morrisonite, nolzeite, packratite, vanarsite and a new data on nalivkinite. # Bulgakite* and New Data on Nalivkinite {#article-title-2} A.A. Agakhanov, L.A. Pautov, E. Sokolova, Y.A. Abdu and V.Y. Karpenko (2016) Two astrophyllite-supergroup minerals: bulgakite, a new mineral from the Darai-Pioz alkaline massif, Tajikistan and revision of the crystal structure and chemical formula of nalivkinite. Canadian Mineralogist, 54(1), 33–48. Bulgakite, (IMA 2014-041), ideally ![Formula][1] , is a new astrophyllite-supergroup mineral. It occurs in the moraine of the Darai-Pioz glacier (39°30′N 70°40′E) in the upper Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, in the area of the joint Turkestan, Zeravshan, and Alay Ranges, Tajikistan. The Darai-Pioz massif is a multiphase intrusion and occupies the core of a large synclinal fold of Carboniferous (Pennsylvanian series) slates. Rocks of the massif have been intruded by fine-grained dikes of biotite tourmaline granites and veins of calcite carbonatites and fenites. Bulgakite was found in a naturally tumbled amphibole–quartz–feldspar boulder of spotty texture, as individual crystals and intergrowths in small cavities (up to 0.5 cm) and as intergrowths (up to 1 cm) of platy crystals and aggregates of poorly crystallized grains. Associated minerals are alkali amphibole, quartz, microcline, bafertisite, aegirine, calcybeborosilite-(Y) , thorite, fluorite, and later crystallized brannockite and sogdianite. Bulgakite is brownish orange with a pale brown streak and a vitreous luster. Cleavage is perfect parallel to {001} and moderate parallel to {010}. The indentation hardness of bulgakite is VHN50 = … [1]: /embed/mml-math-1.gif

Single-crystal X-ray diffraction, EMPA, FTIR and X-ray photoelectron spectroscopy study of narsarsukite from Murun Massif, Russia

AbstractA crystal chemical study of narsarsukite from the Murun alkaline massif, Russia has been carried out combining single-crystal X-ray diffraction, electron microprobe analyses, micro-Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The narsarsukite single crystals are tetragonal (space group I4/m) with unit-cell parameters: 10.7140(1) ≤ a ≤ 10.7183(2) Å and 7.9478(1) ≤ c ≤ 7.9511(1) Å. The XPS analysis showed that Fe occurs in the mineral as Fe3+, whereas the FTIR spectrum showed that the sample studied is anhydrous. The average crystal chemical formula of the Murun narsarsukite is: Na2.04K0.01(V0.015+Ti0.74Zr0.01Al0.01Fe0.223+Mg0.01)1.00Si4.00(O10.74F0.23OH0.03)11.00. Structural disorder at octahedral and interstitial sites was modelled and also discussed in consideration of the main substitutional mechanism Ti4+ + O2– ↔ Fe3+ + (F–, OH–) active in the structure of the mineral.

Thermal behavior analysis of halloysite selected from Inner Mongolia Autonomous Region in China

Thermal behavior of halloysite selected from Erdos, Inner Mongolia Autonomous Region in China, was investigated by thermogravimetry and differential thermal gravity (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscope (SEM). The XRD results indicated that the mineralogical composition of halloysite sample was determined as 7 A halloysite with the d (001) value of 0.734 nm, a small amount of 10 A halloysite with the d (001) value of 0.998 nm, quartz, calcite, anhydrite, siderite, and analcite. The crystal chemical formula of halloysite specimen is (Ca0.007Na0.039K0.048)(Al1.935Fe 0.032 3+ Mn 0.003 2+ Ti 0.002 4+ Mg 0.015 2+ Ca 0.021 2+ )2 [(Si1.935Al 0.065 3+ )2](OH)4·2H2O according to the oxygen atom method. The TG–DTG–DSC data showed that a small amount of water molecule layer in the interlayer and the dehydroxylation was observed at 493.6 °C. The XRD, FT-IR, and SEM data clearly show that the structure changes and dehydroxylation of the halloysite with the temperature increased from 200 to 1200 °C. The dehydration of the halloysite is followed by the loss of intensity and evolution of the OH vibration bands and the change in microstructure. Dehydroxylation is followed by the decrease in the intensity of the bands at 3696 and 3620 cm−1, which is completely disappeared at 700 °C. The thermal behavior of halloysite was influenced by the mineralogy composition and impurities.

Tatarinovite Са3Al(SO4)[В(ОH)4](ОH)6 · 12H2O, a new ettringite-group mineral from the Bazhenovskoe deposit, Middle Urals, Russia, and its crystal structure

A new mineral, tatarinovite, ideally Са3Аl(SO4)[В(ОН)4](ОН)6 · 12Н2O, has been found in cavities of rhodingites at the Bazhenovskoe chrysotile asbestos deposit, Middle Urals, Russia. It occurs (1) colorless, with vitreous luster, bipyramidal crystals up to 1 mm across in cavities within massive diopside, in association with xonotlite, clinochlore, pectolite and calcite, and (2) as white granular aggregates up to 5 mm in size on grossular with pectolite, diopside, calcite, and xonotlite. The Mohs hardness is 3; perfect cleavage on (100) is observed. D meas = 1.79(1), D calc = 1.777 g/cm3. Tatarinovite is optically uniaxial (+), ω = 1.475(2), e = 1.496(2). The IR spectrum contains characteristic bands of SO4 2−, CO3 2−, B(OH)4 −, B(OH)3, Al(OH)6 3-, Si(OH)6 2-, OH–, and H2O. The chemical composition of tatarinovite (wt %; ICP-AES; H2O was determined by the Alimarin method; CO2 was determined by selective sorption on askarite) is as follows: 27.40 CaO, 4.06 B2O3, 6.34 A12O3, 0.03 Fe2O3, 2.43 SiO2, 8.48 SO3, 4.2 CO2, 46.1 H2O, total is 99.04. The empirical formula (calculated on the basis of 3Ca apfu) is H31.41Ca3.00(Al0.76Si0.25)Σ1.01 · (B0.72S0.65C0.59)Σ1.96O24.55. Tatarinovite is hexagonal, space gr. P63, a = 11.1110(4) A, c = 10.6294(6) A, V = 1136.44(9) A3, Z = 2. Its crystal chemical formula is Са3(Аl0.70Si0.30) · {[SO4]0.34[В(ОН)4]0.33[СO3]0.24}{[SO4]0.30[В(ОН)4]0.34[СО3]0.30[В(ОН)3]0.06}(ОН5·73О0.27) · 12Н2O. The strongest reflections of the powder X-ray diffraction pattern [d, A (I, %) (hkl)] are 9.63 (100) (100), 5.556 (30) (110), 4.654 (14) (102), 3.841 (21) (112), 3.441 (12) (211), 2.746 (10) (302), 2.538 (12) (213). Tatarinovite was named in memory of the Russian geologist and petrologist Pavel Mikhailovich Tatarinov (1895–1976), a well-known specialist in chrysotile asbestos deposits. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.

Ferrorhodonite, CaMn3Fe[Si5O15], a new mineral species from Broken Hill, New South Wales, Australia

The new mineral ferrorhodonite, a Mn2+–Fe2+ ordered analogue of rhodonite with the idealized formula CaMn3Fe[Si5O15], was found in the manganese-rich metamorphic rocks of the Broken Hill Pb–Zn–Ag deposit, Yancowinna Co., New South Wales, Australia. Ferrorhodonite occurs as brownish red coarsely crystalline aggregates in association with galena, chalcopyrite, spessartine, and quartz. The mineral is brittle. Its Mohs hardness is 6. Cleavage is perfect on {201} and good on {021} and {210}. The measured and calculated values of density are 3.71 (2) and 3.701 g cm−3, respectively. Ferrorhodonite is optically biaxial positive, with α = 1.731 (4), β = 1.736 (4), γ = 1.745 (5) and 2 V (meas.) = 80 (10)°. The average chemical composition of ferrorhodonite is (electron-microprobe data, wt%): CaO 7.09, MgO 0.24, MnO 32.32, FeO 14.46, ZnO 0.36, SiO2 46.48, and total 100.95. The empirical formula calculated on 15 O apfu (Z = 2) is Ca0.81Mn2.92Fe1.29Mg0.04Zn0.03Si4.96O15. The Mossbauer and IR spectra are reported. The strongest reflections in the powder X-ray diffraction pattern [(d, A (I, %) (hkl)] are: 3.337 (32) (−1–13), 3.132 (54) (−210), 3.091 (41) (0–23), 2.968 (100) (−2–11), 2.770 (91) (022), 2.223 (34) (−204), 2.173 (30) (−310). Ferrorhodonite is isostructural with rhodonite. The crystal structure was solved based on single-crystal X-ray diffraction data and refined to R 1 = 4.02% [for 3114 reflections with I > 2σ(I)]. The mineral is triclinic, space group P $$\bar{1}$$ , a = 6.6766 (5), b = 7.6754 (6), c = 11.803 (1) A, α = 105.501 (1)°, β = 92.275 (1)°, γ = 93.919 (1)°; V = 580.44 (1). The crystal-chemical formula of ferrorhodonite inferred to be: M5(Ca0.81Mn0.19) M1−3(Mn2.52Fe0.48) M4(Fe 0.81 2+ Mn0.12Mg0.04Zn0.03) [Si5O15]. .

Towards a revisitation of vesuvianite-group nomenclature: the crystal structure of Ti-rich vesuvianite from Alchuri, Shigar Valley, Pakistan.

Vesuvianite containing 5.85 wt% TiO2 from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, Pakistan, has been investigated by means of electron microprobe analyses, gas-chromatographic analysis of H2O, X-ray powder diffraction, single-crystal X-ray structure refinement, 27Al NMR, 57Fe Mössbauer spectroscopy, IR spectroscopy and optical measurements. Tetragonal unit-cell parameters are: a = 15.5326 (2), c = 11.8040 (2) Å, space group P4/nnc. The structure was refined to final R1 = 0.031, wR2 = 0.057 for 11247 I > 2σ(I). A general crystal-chemical formula of studied sample can be written as follows (Z = 2): [8-9](Ca17.1Na0.9) [8]Ca1.0[5](Fe2+0.44Fe3+0.34Mg0.22) [6](Al3.59Mg0.41) [6](Al4.03Ti2.20Fe3+1.37Fe2+0.40) (Si18O68) [(OH)5.84O2.83F1.33]. The octahedral site Y2 is Al-dominant and does not contain transition elements. Another octahedral site Y3 is also Al-dominant and contains Fe2+, Fe3+ and Ti. The site Y1 is split into Y1a and Y1b predominantly occupied by Fe2+ and Fe3+, respectively. The role of the Y1 site in the diversity of vesuvianite-group minerals is discussed.

Synthesis and crystal structure of Ga-rich, Fe-bearing tourmaline

Crystals of Ga-rich, Fe-bearing tourmaline (∼25 wt% Ga2O3, 11 wt% FeOtotal) were grown from hydrothermal solution at 100 MPa and 600°C. The crystals were grown on a seed as a newly formed, up to 200 μm thick layer and, in addition, as free, spontaneously nucleated elongated prisms, 10 to 200 μm in size. The crystal structure of the synthetic tourmaline was studied by Mossbauer spectroscopy and single-crystal X-ray diffraction (to an R -index of 0.032; a = 16.000 (1), c = 7.257(1) A). Gallium and iron cations are distributed over the Y and Z octahedral sites according to the crystal-chemical formula (Na0.95□0.05) (Ga1.34Fe2+ 0.62Al0.44Fe3+ 0.34Ni0.26) (Al3.28Ga1.92 Fe2+ 0.41Fe3+0.39) (Si6O18) (BO3)3 (OH2.29O0.71) (O), suggesting that the disordered distribution previously shown for Al3+ also holds for other trivalent cations in tourmalines.

Pseudomalachite–cornwallite and kipushite–philipsburgite solid solutions: chemical composition and Raman spectroscopy

A suite of 60 mineral samples with compositions intermediate between pseudomalachite, Cu 5 (PO 4 ) 2 (OH) 4 , and its arsenate analogue cornwallite, and between kipushite, (Cu,Zn) 6 (PO 4 ) 2 (OH) 6 ·H 2 O, and its arsenate analogue philipsburgite was investigated by electron-probe microanalysis, scanning electron microscopy, powder X-ray diffraction and micro-Raman spectroscopy. A wide range of compositions was found, covering 77.5 mol% and 75 mol% of the cornwallite–pseudomalachite and kipushite–philipsburgite solid solutions, respectively, demonstrating an extended P ↔ As substitution in these minerals. The analyses also reveal a Zn deficiency in the tetrahedral site of the kipushite–philipsburgite structure, leading to the crystal-chemical formula [4] (Zn,Cu) [6] Cu 5 (P 1−x As x O 4 ) 2 (OH) 6 ·H 2 O for this series. Raman spectra of the pseudomalachite–cornwallite solid solution are sensitive to the P/(As + P) ratio. The up-shift of a band assigned to the symmetric stretching vibrations of (AsO 4 ) group recorded in Raman spectra of the arsenate pseudomalachite is indicative of shortening As–O bonds and of bond-angle adjustment to accommodate the large As ions in the pseudomalachite structure. This feature is less evident in the arsenate kipushite, perhaps due its larger cell volume, where larger ions can be more easily accommodated in the anionic sublattice. Raman imaging and cluster analysis were applied to reveal chemical heterogeneity and structural disorder in the kipushite–philipsburgite solid solution.

Crystal structure of magnesio-ferri-hornblendite □Ca2(Mg4Fe3+)[(Si7Al)O22](OH)2 as a potentially new mineral of the amphibole supergroup

A sample of magnesio-ferri-hornblendite, a potential new mineral of the amphibole supergroup, was studied by X-ray diffraction and IR spectroscopy. The crystal chemical formula is (Z = 2): AK0.04M(4) (Ca1.92Na0.08) C[M(1)(Mg1.78Fe0.224+) M(2)(Mg1.62Fe0.263+Al0.12) M(3)(Mg0.64Fe0.322+Mn0.04)] [T(Si7.44Al0.56)O22] W(OH)2. The monoclinic unit cell parameters are a = 9.855(1) A, b = 18.084(1) A, c = 5.289(1) A, β = 104.853(2)°; V = 911.1(2) A3; space group C2/m; Z = 2. The crystal structure was refined to R = 2.82% in the anisotropic approximation for atomic displacement parameters using 1166 reflections with I > 2σ(I). The magnesio-ferri-hornblendite structure is generally similar to the structures of other monoclinic calcium amphiboles, and its key distinctive features are the predominance of Мg among C2+ cations and Fe3+ among C3+ cations.

ChemInform Abstract: Donharrisite, Ni3HgS3: Crystal Structure and Revision of the Chemical Formula.

AbstractThe title mineral crystallizes in the monoclinic space group C2/m with Z = 4 (single crystal XRD).

Uraninite from the Olympic Dam IOCG-U-Ag deposit: Linking textural and compositional variation to temporal evolution

The Olympic Dam IOCG-U-Ag deposit, South Australia, the world’s largest known uranium (U) resource, contains three main U-minerals: uraninite, coffinite, and brannerite. Four main classes of uraninite have been identified. Uraninite occurring as single grains is characterized by high-Pb and ΣREE+Y (ΣREY) but based on textures can be classified into three of these classes, typically present in the same sample. Primary uraninite (Class 1) is smallest (10–50 μm), displays a cubic-euhedral habit, and both oscillatory and sectorial zoning. “Zoned” uraninite (Class 2) is coarser, sub-euhedral, and combines different styles of zonation in the same grain. “Cobweb” uraninite (Class 3) is coarser still, up to several hundred micrometers, has variable hexagonal-octagonal morphologies, varying degrees of rounding, and features rhythmic intergrowths with sulfide minerals. In contrast, the highest-grade U in the deposit is found as micrometer-sized grains to aphanitic varieties of uraninite that form larger aggregates (up to millimeter) and vein-fillings (massive, Class 4) and have lower Pb and ΣREY, but higher Ca. Nanoscale characterization of primary and cobweb uraninite shows these have defect-free fluorite structure. Both contain lattice-bound Pb+ΣREY, which for primary uraninite is concentrated within zones, and for cobweb uraninite is within high-Pb+ΣREY domains. Micro-fractured low-Pb+ΣREY domains, sometimes with different crystal orientation to the high-Pb+ΣREY domains in the same cobweb grain, contain nanoscale inclusions of galena, Cu-Fe-sulfides, and REY-minerals. The observed Pb zonation and presence of inclusions indicates solid-state trace-element mobility during the healing of radiogenic damage, and subsequent inclusion-nucleation + recrystallization during ![Formula][1] -driven percolation of Cu-bearing fluid. Tetravalent, lattice-bound radiogenic Pb is proposed based on analogous evidence for U-bearing zircon. Calculating the crystal chemical formula to UO2 stoichiometry, the sum of cations (M*) is ~1 for most classes, but the presence of mono-, di-, and trivalent elements (ΣREY, Ca, etc.) drive stoichiometry toward hypostoichiometric M*O2–x. In the absence of measured O and constraints of hypostoichiometric fluorite-structure, charge-balance calculations showing O deficit in the range 0.15–0.36 apfu is compensated by assumption of mixed U oxidation states. Crystal structural formulas show up to 0.20 apfu Pb and 0.25 apfu ΣREY in Classes 1–3, while for Class 4, these are an order of magnitude less. Low-Pb and ΣREY subcategories of Classes 2 and 3 are similar to massive uraninite with ~0.2 apfu Ca. Other elements (Si, Na, Mn, As, Nb, etc.), show two distinct geochemical trends: (1) across Classes 1–3; and (2) Class 4, whereby low-Pb+ΣREY sub-populations of Classes 2 and 3 are part of trend 2 for certain elements. Plots of alteration factor (CaO+SiO2+Fe2O3) vs. Pb/U suggest two uraninite generations: early (high-Pb+ΣREY, Classes 1–3); and late (massive, Class 4). There is evidence of Pb loss from diffusion, leaching and/or recrystallization for Classes 2–3 (low-Pb+ΣREY domains). Micro-analytical data and petrographic observations reported here, including nanoscale characterization of individual uraninite grains, support the hypothesis for at least two main uraninite mineralizing events at Olympic Dam and multiple stages of U dissolution and reprecipitation. Early crystalline uraninite is only sparsely preserved, with the majority of uraninite represented by the massive-aphanitic products of post-1590 Ma dissolution, reprecipitation, and possibly addition of uranium into the system. Coupled dissolution-reprecipitation reactions are suggested for early uraninite evolution across Classes 1 to 3. The calculated oxidation state [U6+/(U4++U6+)] of the “early” and “late” populations point to different conditions at the time of formation (charge compensation for ΣREY-rich early fluids) rather than auto-oxidation of uraninite. Late uraninites may have formed hydrothermally at lower temperatures ( T < 250 °C). [1]: /embed/mml-math-1.gif

Donharrisite, Ni3HgS3: Crystal structure and revision of the chemical formula

The crystal structure of the mineral donharrisite, a rare nickel-mercury-sulfide reported in the literature with the formula Ni8Hg3S9, was solved and refined using intensity data collected from a crystal from Leogang, Salzburg Province, Austria. This study revealed that the structure is monoclinic, space group C2/m, with a = 11.574(3), b = 6.899(2), c = 5.419(1) Å, β = 93.71(2)° and V = 431.8(2) Å3. The refinement of an anisotropic model led to an R index of 0.044 for 383 independent reflections.In the crystal structure there are two Hg sites, four Ni sites and 2 S, with one Hg and one Ni site which are half-occupied. As typical of many intermetallic compounds, the donharrisite structure is characterized by atoms forming complex polyhedra as Hg[S6Ni4], Hg[S4Ni3], Ni[S4Ni2], Ni[S3NiHg], Ni[S6Ni2Hg2], Ni[S4Ni3Hg2], showing exceedingly short bond distances. Electron microprobe analyses of the crystal used for the structural study led to the formula Ni3.03Hg1.01S2.96, on the basis of 7 atoms. On the basis of information gained from this characterization the crystal chemical formula was revised according to the structural results, yielding Ni3HgS3 with Z = 4 (with a calculated density of 7.27 g/cm3), instead of Ni8Hg3S9 with Z = 2 (with a calculated density of 5.18 g/cm3) as previously reported.Although neither reflection streaks nor structural disorder were observed for the selected donharrisite crystal, the possibility that the refined structure (with partially-occupied sites and exceedingly short bond distances) could be a superposition of different layers belonging to an OD (order-disorder) structure is also discussed.

Crystal chemistry of a Ba-dominant analogue of hydrodelhayelite and natural ion-exchange transformations in double- and triple-layer phyllosilicates in post-volcanic systems of the Eifel region, Germany

A Ba-dominant (Ba > K) analogue of hydrodelhayelite (BDAH) from Lohley (Eifel Mts., Rhineland-Palatinate, Germany) and Ba-enriched varieties of related double- and triple-layer phyllosilicates from Eifel are studied. The crystal structure of BDAH was solved by direct methods and refined to R = 0.0698 [1483 unique reflections with I > 2σ(I)]. It is orthorhombic, Pmmn, a = 23.9532(9), b = 7.0522(3), c = 6.6064(3) A, V = 1115.97(8) A3, Z = 2. The structure is based upon delhayelite-type double-layer tetrahedral blocks [(Al,Si)4Si12O34(OH,O)4] connected by chains of (Ca,Fe)-centered octahedra. Ba2+ and subordinate K+ occur at partially vacant sites in zeolitic channels within the tetrahedral blocks. The crystal-chemical formula of BDAH is: (Ba0.42K0.34□0.24)(Ca0.88Fe0.12)2(□0.90Mg0.10)2[Si6(Al0.5Si0.5)2O17(OH0.71O0.29)2]⋅6H2O. The formation of BDAH and Ba-rich varieties of altered delhayelite/fivegite, gunterblassite and hillesheimite is considered as a result of leaching of Na, Cl, F and, partially, K and Ca accompanied with hydration and the capture of Ba as a result of natural ion exchange. These minerals are structurally a “bridge” between single-layer phyllosilicates and zeolites having the open three-dimensional tetrahedral Al-Si-O frameworks.

Polysomatism and structural complexity: structure model for murataite-8C, a complex crystalline matrix for the immobilization of high-level radioactive waste

Murataite-8 C , a prospective synthetic material for the long-term immobilization of high-level radioactive waste and a member of the pyrochlore–murataite polysomatic series, was investigated by means of single-crystal X-ray diffraction. The crystal structure (cubic, F -43 m , a = 39.105(12) A, V = 59799(32) A3, Z = 4) is of outstanding complexity and contains forty symmetrically independent cation sites. Its crystal-chemical formula determined on the basis of the crystal-structure refinement, Al25.44Ca55.96Ti282.20Mn53.72Fe17.24Zr15.00Ho36.64O823, is in good agreement with the empirical formula calculated from electron-microprobe data, Al23.02Ca52.85Ti284.10Mn54.31Fe17.59Zr14.83Ho38.04O823. The crystal structure is based upon a three-dimensional octahedral framework that can be described as an alternation of murataite and pyrochlore modules immersed into a transitional substructure that combine elements of the crystal structures of murataite-3 C and pyrochlore. The obtained structural model confirms the polysomatic nature of the pyrochlore–murataite series and illuminates the chemical and structural peculiarities of crystallization of the murataite-type titanate ceramic matrices. The high chemical and structural complexity of the members of the pyrochlore–murataite series is unparalleled in the world of crystalline materials proposed for the high-level radioactive waste immobilization, which makes it unique and promising for further technological and scientific exploration.

Crystal Structure Refinements of Isomertieite, Pd11Sb2As2, and Törnroosite, Pd11As2Te2

Abstract The crystal structures of isomertieite, Pd 11 Sb 2 As 2 , (I) from the Monche-Tundra intrusion, Monchegorsk Igneous Complex (MIC), Kola Peninsula, Russia, and tornroosite, Pd 11 As 2 (Te 1.7 Bi 0.3 ) Σ2 (IIa) and Pd 11 As 2 (Te 1.3 Bi 0.7 ) Σ2 (IIb) from the South Sopcha intrusion, MIC, Kola Peninsula, Russia, were refined on the basis of X-ray diffraction data collected from single crystals. The two minerals were found to exhibit the same structure, cubic, space group Fd m , Z = 8, with unit-cell parameters for (I): a 12.297(5) A, V 1859.3(2) A 3 ; for (IIa): a 12.350(2) A, V 1883.6(4) A 3 ; and for (IIb): a 12.370(1) A, V 1892.9(3) A 3 . The structures were refined to R 1 = 0.056 (I), 0.014 (IIa), 0.018 (IIb). The isomertieite crystal-chemical formula was confirmed. The Bi-for-Te substitution in tornroosite was found to not affect the main structural topology. In the structure of the two minerals there are three symmetrically independent Pd positions: M 1, M 2, and M 3. M 1 forms M 1As 4 tetrahedra, M 2 forms M 2As 2 Sb 2 (I) or M 2As 2 Te 2 (II) tetrahedra, and M 3 forms M 3Sb 3 (I) or M 3Te 3 (II) triangles connected together via common edges and forming a framework in the structure.