Jahnsite-(CaMnZn) from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, and structural flexibility of jahnsite-group minerals

2020 ◽  
Vol 84 (4) ◽  
pp. 547-553
Author(s):  
Ian E. Grey ◽  
Erich Keck ◽  
Anthony R. Kampf ◽  
Colin M. MacRae ◽  
John D. Cashion ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Empirical Formula ◽  
Structural Flexibility ◽  
Optical Orientation ◽  
Calculated Density ◽  
Nomenclature System ◽  
Group Mineral ◽  
International Mineralogical Association ◽  
Mineralogical Association ◽  
Orthogonal Orientation

AbstractJahnsite-(CaMnZn), CaMn2+Zn2Fe3+2(PO4)4(OH)2⋅8H2O, is a new jahnsite-group mineral associated with alteration of phosphophyllite at the Hagendorf-Süd pegmatite, Bavaria. It forms as thin yellow crusts and brown epitactic growths on altered phosphophyllite, both of which comprise lath-like crystals in orthogonal orientation, up to 100 μm long. The crystals contain intergrowths of jahnsite-(CaMnZn) and jahnsite-(CaMnMn) on a scale of ~50 μm. The calculated density is 2.87 g cm−3 based on the empirical formula. Optically it is biaxial (–), with α = 1.675(2), β = 1.686(2) and γ = 1.691(2) (white light). The calculated 2V is 68°. Dispersion could not be observed, and the optical orientation is Z = b. Pleochroism was imperceptible. Electron microprobe analyses together with results from Mössbauer spectroscopy gives the formula (Ca0.59Mn0.24)Σ0.83Mn(Zn0.74Mn2+0.48Mg0.18Fe2+0.13Fe3+0.47)Σ2Fe3+2(P0.995O4)4(OH)2.03(H2O)7.97.Jahnsite-(CaMnZn) is monoclinic, P2/a, with a = 15.059(1), b = 7.1885(6), c = 10.031(2) Å, β = 111.239(8)° and V = 1012.1(2) Å3. The recent International Mineralogical Association approved nomenclature system for jahnsite-group minerals was applied to establish jahnsite-(CaMnZn) from the empirical formula. The structural flexibility of jahnsite-group minerals to accommodate cations of quite different sizes in the X and M1 sites is discussed in terms of rotations about the 7 Å axis of two independent octahedra centred at the M3 sites.

Kummerite, Mn2+Fe3+Al(PO4)2(OH)2·8H2O, a new laueite-group mineral from the Hagendorf Süd pegmatite, Bavaria, with ordering of Al and Fe3+

2016 ◽  
Vol 80 (7) ◽  
pp. 1243-1254 ◽  
Author(s):  
I. E. Grey ◽  
E. Keck ◽  
W. G. Mumme ◽  
A. Pring ◽  
C. M. Macrae ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Empirical Formula ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Calculated Density ◽  
Group Mineral ◽  
X Ray ◽  
Cell Parameters ◽  
Octahedral Sites ◽  
Phosphate Mineral

AbstractKummerite, ideally Mn2+Fe3+A1(PO4)2(OH)2.8H2O, is a new secondary phosphate mineral belonging to the laueite group, from the Hagendorf-Süd pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany. Kummerite occurs as sprays or rounded aggregates of very thin, typically deformed, amber yellow laths. Cleavage is good parallel to ﹛010﹜. The mineral is associated closely with green Zn- and Al-bearing beraunite needles. Other associated minerals are jahnsite-(CaMnMn) and Al-bearing frondelite. The calculated density of kummerite is 2.34 g cm 3. It is optically biaxial (-), α= 1.565(5), β = 1.600(5) and y = 1.630(5), with weak dispersion. Pleochroism is weak, with amber yellow tones. Electron microprobe analyses (average of 13 grains) with H2O and FeO/Fe2O3 calculated on structural grounds and normalized to 100%, gave Fe2O3 17.2, FeO 4.8, MnO 5.4, MgO 2.2, ZnO 0.5, Al2O3 9.8, P2O5 27.6, H2O 32.5, total 100 wt.%. The empirical formula, based on 3 metal apfu is (Mn2+0.37Mg0.27Zn0.03Fe2+0.33)Σ1.00(Fe3+1.06Al0. 94)Σ2.00PO4)1.91(OH)2.27(H2O)7.73. Kummerite is triclinic, P1̄, with the unit-cell parameters of a = 5.316(1) Å, b =10.620(3) Å , c = 7.118(1) Å, α = 107.33(3)°, β= 111.22(3)°, γ = 72.22(2)° and V= 348.4(2) Å3. The strongest lines in the powder X-ray diffraction pattern are [dobs in Å(I) (hkl)] 9.885 (100) (010); 6.476 (20) (001); 4.942 (30) (020); 3.988 (9) (̄110); 3.116 (18) (1̄20); 2.873 (11) (1̄21). Kummerite is isostructural with laueite, but differs in having Al and Fe3+ ordered into alternate octahedral sites in the 7.1 Å trans-connected octahedral chains.

Canutite, NaMn3[AsO4][AsO3(OH)]2, a new protonated alluaudite-group mineral from the Torrecillas mine, Iquique Province, Chile

2014 ◽  
Vol 78 (4) ◽  
pp. 787-795 ◽  
Author(s):  
A. R. Kampf ◽  
S. J. Mills ◽  
F. Hatert ◽  
B. P. Nash ◽  
M. Dini ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
White Light ◽  
Electron Microprobe ◽  
New Mineral ◽  
Optical Orientation ◽  
Calculated Density ◽  
Secondary Alteration ◽  
Group Mineral ◽  
X Ray ◽  
Mohs Hardness

AbstractThe new mineral canutite (IMA2013-070), NaMn3[AsO4][AsO3(OH)]2, was found at two different locations at the Torrecillas mine, Salar Grande, Iquique Province, Chile, where it occurs as a secondary alteration phase in association with anhydrite, halite, lavendulan, magnesiokoritnigite, pyrite, quartz and scorodite. Canutite is reddish brown in colour. It forms as prisms elongated on [20] and exhibiting the forms {010}, {100}, {10}, {201} and {102}, or as tablets flattened on {102} and exhibiting the forms {102} and {110}. Crystals are transparent with a vitreous lustre. The mineral has a pale tan streak, Mohs hardness of 2½, brittle tenacity, splintery fracture and two perfect cleavages, on {010} and {101}. The calculated density is 4.112 g cm−3. Optically, canutite is biaxial (+) with α = 1.712(3), β = 1.725(3) and γ = 1.756(3) (measured in white light). The measured 2V is 65.6(4)°, the dispersion is r < v (slight), the optical orientation is Z = b; X ^ a = 18° in obtuse β and pleochroism is imperceptible. The mineral is slowly soluble in cold, dilute HCl. The empirical formula (for tabular crystals from near the mineshaft), determined from electron - microprobe analyses, is (Na1.05Mn2.64Mg0.34Cu0.14Co0.03)∑4.20As3O12H1.62. Canutite is monoclinic, C2/c, a = 12.3282(4), b = 12.6039(5), c = 6.8814(5) Å, β = 113.480(8)°, V = 980.72(10) Å3 and Z = 4. The eight strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 6.33(34)(020), 4.12(26)(21), 3.608(29)(310,31), 3.296(57)(12), 3.150(28)(002,131), 2.819(42)(400,041,330), 2.740(100)(240,02,112) and 1.5364(31)(multiple). The structure, refined to R1 = 2.33% for 1089 Fo > 4σF reflections, shows canutite to be isostructural with protonated members of the alluaudite group.

Mcalpineite, Cu3TeO6·H2O, a new mineral from the McAlpine mine, Tuolumne County, California, and from the Centennial Eureka mine, Juab County, Utah

1994 ◽  
Vol 58 (392) ◽  
pp. 417-424 ◽  
Author(s):  
Andrew C. Roberts ◽  
T. Scott Ercit ◽  
Alan J. Criddle ◽  
Gary C. Jones ◽  
R. Scott Williams ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Empirical Formula ◽  
Infrared Absorption Spectrum ◽  
Short Wave ◽  
New Mineral ◽  
Calculated Density ◽  
Reflected Light ◽  
Lattice Space ◽  
Copper Zinc ◽  
Dark Green

AbstractMcalpineite, ideally Cu3TeO6·H2O, occurs as isolated 0.5 mm-sized emerald green cryptocrystalline crusts on white quartz at the long-abandoned McAlpine mine, Tuolumne County, California, U.S.A. Associated nonmetallic phases are muscovite (mariposite), calcite, goethite, hematite, chlorargyrite, choloalite, keystoneite, mimetite, malachite, azurite, annabergite and a host of unidentified crusts, both crystalline and amorphous. Associated metallic minerals include pyrite, acanthite, hessite, electrum, altaite, native silver, galena, pyrargyrite, sphalerite and owyheeite. The mineral has also been identified at the Centennial Eureka mine, Juab County, Utah, U.S.A., where it occurs as interstitial olive-green coatings and as millimetre-sized dark green-black cryptocrystalline nodules lining drusy quartz vugs. Associated minerals are xocomecatlite, hinsdalite-svanbergite, goethite and several new species including two hydrated copper tellurates, a hydrated copper-zinc tellurate/tellurite, and a hydrated copper-zinc tellurate/tellurite-arsenate-chloride. Mcalpineite is cubic, P-lattice (space group unknown), a = 9.555(2) Å, V = 872.4(4) Å. The strongest six lines in the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 4.26(40)(210), 2.763(100)(222), 2.384(70)(400), 1.873(40)(431,510), 1.689(80)(440) and 1.440(60)(622). The average of four electron-microprobe analyses (McAlpine mine) is CuO 50.84, NiO 0.17, PbO 4.68, SiO2 0.65, TeO3 39.05, H2O (calc.) [4.51], total [100.00] wt. %. With O = 7, the empirical formula is (Cu2.79Pb0.09Ni0.01)∑2.89(Te0.97Si0.05)∑1.02O5.90·1.10H2O. This gives a calculated density of 6.65. g/cm3 for Z = 8. The average of two electron-microprobe analyses (Centennial Eureka mine) is CuO 51.2, ZnO 3.1, TeO3 39.0, SiO2 0.2, As2O5 0.8, H2O (by CHN elemental analyser) 7, total 101.3 wt. %, leading to the empirical formula (Cu2.56Zn0.15)∑2.71 (Te0.88Si0.02As0.02)∑0.92O5.47·1.53H2O. The infrared absorption spectrum shows definite bands for structural H2O with an O-H stretching frequency centred at 3320 cm−1 and a H-O-H flexing frequency centred at 1600 cm−1. In reflected light Mcalpineite is isotropic, nondescript grey, with ubiquitous brilliant apple to lime green internal reflections. The refractive index calculated from Fresnel equations is 2.01. Measured reflectance values in air and in oil are tabulated. Reflectance study also shows that cryptocrystalline aggregates are composed of micron-sized sheaves of fibrous or prismatic crystals. Other physical properties include: adamantine lustre; light green streak; brittle; uneven fracture; translucent to transparent and nonfluorescent under both long- and short-wave ultraviolet light. The name is for the first known locality, the McAlpine mine.

scholarly journals AMPH-IMA04: a revised Hypercard program to determine the name of an amphibole from chemical analyses according to the 2004 International Mineralogical Association scheme

2004 ◽  
Vol 68 (5) ◽  
pp. 825-830 ◽  
Author(s):  
A. Mogessie ◽  
K. Ettinger ◽  
B. E. Leake
Keyword(s):  
Electron Microprobe ◽  
Association Scheme ◽  
Chemical Analyses ◽  
International Mineralogical Association ◽  
Mineralogical Association ◽  
Single Input ◽  
Input Format

AbstractIn 2004, the International Mineralogical Association (IMA) amended the IMA 97 amphibole classification and nomenclature scheme byadding a fifth group to include the recently discovered B(LiNa) amphiboles ferriwhittakeriite and ferri-ottoliniite, which cannot be fitted into the four major amphibole groups. New root-names such as sodic-pedrizite in the Mg-Fe-Mn-Li group and obertiite and dellaventuraite in the sodic group along with two new prefixes, parvo and magno have also been added. As result it has become necessary to modify the AMPH-IMA97 amphibole-naming program. The new program (AMPH-IMA04) allows single input or automatic input of as many amphibole analyses as are available following a set input format. Any of three different calculation schemes for dealing with an amphibole analysis can be chosen: (1) complete chemical analyses can be calculated to 24(O,OH,F,Cl); (2) analyses with determined FeO and Fe2O3, MnO and Mn2O3 but without H2O can be calculated to 23(O); and (3) electron microprobe analyses with only total Fe determined and without H2O can be calculated to 23(O) with IMA97-recommended normalization for Fe3+ and Fe2+ values. In addition a stoichiometric calculation of Mn2+ and Mn3+ is considered and implemented for the Mn-bearing sodic amphiboles in order to take care of electron microprobe analyses of such amphiboles where the total Mn is given as Mn2+.

Mauriziodiniite, NH4(As2O3)2I, the ammonium and iodine analogue of lucabindiite from the Torrecillas mine, Iquique Province, Chile

2019 ◽  
Vol 84 (2) ◽  
pp. 267-273
Author(s):  
Anthony R. Kampf ◽  
Barbara P. Nash ◽  
Arturo A. Molina Donoso
Keyword(s):  
White Light ◽  
Electron Microprobe ◽  
Empirical Formula ◽  
New Mineral ◽  
Calculated Density ◽  
Secondary Alteration ◽  
Layer Sequence ◽  
Mohs Hardness ◽  
Elastic Fracture ◽  
White Streak

AbstractThe new mineral mauriziodiniite (IMA2019-036), NH4(As2O3)2I, was found at the Torrecillas mine, Iquique Province, Chile, where it is a secondary alteration phase associated with calcite, cuatrocapaite-(NH4), lavendulan, magnesiokoritnigite and torrecillasite on matrix consisting of native arsenic, arsenolite and pyrite. Mauriziodiniite occurs as hexagonal tablets up to ~300 μm in diameter. Crystals are colourless and transparent, with pearly to adamantine lustre and white streak. The Mohs hardness is ~1. Tablets are sectile and easily flexible, but not elastic. Fracture is curved, irregular and stepped. Cleavage is perfect on {001}. The calculated density is 3.916 g/cm3. Optically, mauriziodiniite is uniaxial (–) with ω = 2.07(calc) and ɛ = 1.770(5) (white light). The empirical formula, determined from electron microprobe analyses, is (NH4)0.94K0.03(As2O3)2I0.92Cl0.03. Mauriziodiniite is hexagonal, P6/mmm, a = 5.289(2), c = 9.317(2) Å, V = 225.68(18) Å3 and Z = 1. The structure, refined to R1 = 4.16% for 135 Io > 2σI reflections, contains three types of layers: (1) a planar neutral As2O3 (arsenite) sheet; (2) an NH4+ layer that links adjacent arsenite sheets via bonds to their O atoms; and (3) an I– layer that links adjacent arsenite sheets via bonds to their As atoms. The layer sequence is I–As2O3–NH4–As2O3–I. Mauriziodiniite is isostructural with lucabindiite and is structurally related to gajardoite, cuatrocapaite-(NH4), cuatrocapaite-(K) and torrecillasite.

scholarly journals Levantite, KCa3(Al2Si3)O11(PO4), a new latiumite-group mineral from the pyrometamorphic rocks of the Hatrurim Basin, Negev Desert, Israel

2019 ◽  
Vol 83 (5) ◽  
pp. 713-721 ◽  
Author(s):  
Evgeny V. Galuskin ◽  
Biljana Krüger ◽  
Irina O. Galuskina ◽  
Hannes Krüger ◽  
Yevgeny Vapnik ◽  
...  
Keyword(s):  
Negev Desert ◽  
Double Layers ◽  
Indentation Hardness ◽  
Optical Orientation ◽  
Unit Cell Parameters ◽  
Calculated Density ◽  
Group Mineral ◽  
Cell Parameters ◽  
Optical Axes ◽  
Micro Indentation

AbstractLevantite, with the end-member formula KCa3(Al2Si3)O11(PO4), is the phosphate analogue of latiumite, KCa3(Al3Si2)O11(SO4, CO3) found in gehlenite–wollastonite hornfels on Har Parsa, Negev Desert, Israel. Levantite forms later zones on long-prismatic crystals of latiumite. Rarer homogeneous colourless levantite crystals up to 0.2 mm long and with mean composition (K0.94Ba0.01Na0.01□0.04)Σ1.00(Ca2.96Mg0.03)Σ2.99{(Si2.69Al2.06Fe3+0.16P0.06)Σ4.97O11}[(PO4)0.65(SO4)0.35]Σ1.00 were noted. Minerals of the levantite–latiumite series are associated with gehlenite, wollastonite, clinopyroxene of the esseneite–diopside series, anorthite and Ti-bearing andradite. Levantite crystalises in space group P21 with unit-cell parameters a = 12.1006(9) Å, b = 5.1103(4) Å, c = 10.8252(9) Å, β = 107.237(8)°, V = 639.34(9) Å3 and Z = 2. The structure of levantite is analogous to latiumite. It is formed by tetrahedral hybrid zweier double layers [(Si,Al)10O22] connected by Ca atoms. Three Ca atoms linked to different double layers are bridged over by (PO4) and minor (SO4) groups. K atoms reside in the cavities between two superimposed zweier double layers. The measured micro-indentation hardness of levantite gave VHN50 = 580(19) (mean of 14), range 550–611 kg/mm2, which correlates with 5 on the Mohs scale. Cleavage is good on (100). Twinning on (100) is polysynthetic or simple. The calculated density is 2.957 g cm–3. Levantite is optically negative with α = 1.608(2), β = 1.618(2), γ = 1.622(2) (λ = 589 nm), 2Vmeas. = 70(5)° and 2Vcalc. = 64.3°. Dispersion of the optical axes r > v is weak; the optical orientation is: Z = b, X ^ c = 22–27°; and it is non-pleochroic. Minerals of the levantite–latiumite series from Israel show characteristic Raman spectra with the main bands at 994 cm–1 [ν1(SO4)2–] and 945 cm–1 [ν1(PO4)3–]. The band intensity ν1(PO4)3–/ν1(SO4) ratio is well correlated with P and S contents in the investigated minerals. The strongest lines in the powder diffraction pattern [dobs, Å (I, %) (hkl)] are: 3.0762(100)(310), 2.8551(96)($\bar 2$13), 2.9704(92)($\bar 3$12), 2.8573(83)(013), 2.5552(66)(020), 2.8228(48)(212), 2.8893(40)(400), and 3.0634(30)(103).

Northstarite, a new lead-tellurite-thiosulfate mineral from the North Star mine, Tintic, Utah, USA

2020 ◽  
Vol 58 (4) ◽  
pp. 533-542
Author(s):  
Anthony R. Kampf ◽  
Robert M. Housley ◽  
George R. Rossman
Keyword(s):  
Raman Spectrum ◽  
Powder Diffraction ◽  
Electron Microprobe ◽  
Empirical Formula ◽  
New Mineral ◽  
Calculated Density ◽  
Space Group ◽  
X Ray ◽  
The North ◽  
Mohs Hardness

ABSTRACT Northstarite, Pb6(Te4+O3)5(S2O3), is a new mineral from the North Star mine, Tintic district, Juab County, Utah, USA. It is an oxidation-zone mineral occuring in a vug in massive quartz-baryte-enargite-pyrite in association with anglesite, azurite, chrysocolla, fluorapatite, plumbogummite, tellurite, zincospiroffite, and the new mineral adanite. Crystals are beige short prisms with pyramidal terminations, up to about 1 mm in length. The mineral is transparent to translucent with adamantine luster, white streak, Mohs hardness 2, brittle tenacity, irregular fracture, and no cleavage. The calculated density is 6.888 g/cm3. Northstarite is uniaxial (–) and nonpleochroic. The Raman spectrum is consistent with the presence of tellurite and thiosulfate groups and the absence of OH and H2O. Electron-microprobe analyses gave the empirical formula Pb5.80Sb3+0.05Te4+5.04S6+1.02S2–1.02O18. The mineral is hexagonal, space group P63, with a = 10.2495(5), c = 11.6677(8) Å, V = 1061.50(13) Å3, and Z = 2. The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 3.098(100)(113), 2.957(88)(300), 2.140(42)(223), 1.7335(41)(413), and 1.6256(31)(306). The structure (R1 = 0.033 for 1476 I &gt; 2σI reflections) is a framework constructed of short (strong) Pb–O and Te–O bonds with channels along the 63 axes. The thiosulfate groups at the centers of the channels are only weakly bonded to the framework.

Hagstromite, Pb8Cu2+(Te6+O6)2(CO3)Cl4, a new lead–tellurium oxysalt mineral from Otto Mountain, California, USA

2020 ◽  
Vol 84 (4) ◽  
pp. 517-523
Author(s):  
Anthony R. Kampf ◽  
Robert M. Housley ◽  
Stuart J. Mills ◽  
George R. Rossman ◽  
Joe Marty
Keyword(s):  
Crystal Structure ◽  
Raman Spectrum ◽  
Electron Microprobe ◽  
Optical Orientation ◽  
Framework Structure ◽  
Secondary Oxidation ◽  
Orthorhombic Space Group ◽  
Calculated Density ◽  
Light Yellow ◽  
Mohs Hardness

AbstractHagstromite, Pb8Cu2+(Te6+O6)2(CO3)Cl4, (IMA2019-093) is a new tellurate mineral from Otto Mountain near Baker, California, USA. It occurs on quartz in association with cerussite, fuettererite and thorneite. It is a secondary oxidation zone mineral and is presumed to have formed by oxidation of earlier formed tellurides, chalcopyrite and galena. Hagstromite occurs as light yellow–green blades, up to ~100 μm long. Crystals are transparent with adamantine to silky lustre. The mineral is brittle with two cleavages providing splintery fracture; the Mohs hardness is probably between 2 and 3. The calculated density is 7.062 g cm–3. Hagstromite is optically biaxial (+), with calculated indices of refraction for α = 2.045, β = 2.066 and γ = 2.102; 2Vmeas = 76(1)°; and optical orientation X = b, Y = a and Z = c. The Raman spectrum of hagstromite exhibits similarities with those of agaite and thorneite and confirms the presence of CO32–. The electron microprobe analyses provided the empirical formula Pb8.07Cu2+0.98Te6+1.96C1.17Cl3.83O15.34. Hagstromite is orthorhombic, space group Ibam, with a = 23.688(17), b = 9.026(8), c = 10.461(8) Å, V = 2237(3) Å3 and Z = 4. The crystal structure of hagstromite (R1 = 0.0659 for 284 I > 2σI reflections) contains a novel Cu2+Te6+2O12 chain assembled of corner-sharing Cu2+O4 squares and Te6+O6 octahedra. The O atoms in the chains form bonds with Pb2+ cations, which in turn bond to Cl– and CO32– anions, thereby creating a framework structure.

Petewilliamsite, (Ni,Co)30(As2O7)15, a new mineral from Johanngeorgenstadt, Saxony, Germany: description and crystal structure

2004 ◽  
Vol 68 (2) ◽  
pp. 231-240 ◽  
Author(s):  
A. C. Roberts ◽  
P. C. Burns ◽  
R. A. Gault ◽  
A. J. Criddle ◽  
M. N. Feinglos
Keyword(s):  
Crystal Structure ◽  
Electron Microprobe ◽  
Empirical Formula ◽  
Crystal Structure Analysis ◽  
Index Of Refraction ◽  
Maximum Diameter ◽  
New Mineral ◽  
Monoclinic Space Group ◽  
Calculated Density ◽  
Four Square

AbstractPetewilliamsite, ideally (Ni,Co)30(As2O7)15, monoclinic, space group C2, a = 33.256(5), b = 8.482(1), c = 14.191(2) Å, ß = 104.145(3)°, V = 3881.6(11) Å3, a:b:c = 3.9209:1:1.6731, Z = 2, is a new mineral found on a single nickeline-veined quartz specimen from Johanngeorgenstadt, Saxony, Germany. The mineral possesses a pronounced subcell-supercell: a (subcell) = 1/5 a (supercell); b (subcell) = b (supercell); c (subcell) = 1/3 c (supercell), and the strongest six lines of the X-ray powder-diffraction pattern are [d in Å (I) (hkl)]: 4.235(30)(020) ; 3.118(100)(513, 023); 3.005(60); 2.567(50); 1.637(50)(536 ); 1.507(30b)(553, ). It occurs predominantly as scattered patches of mm-sized aggregates which are intimately associated with varicoloured xanthiosite; additional associations include bunsenite, aerugite, rooseveltite, native bismuth, paganoite and two undefined arsenates. Subhedral equant crystals with rounded faces are intimately intergrown in 1 mm-sized aggregates and individual grains do not exceed 0.5 mm in maximum diameter. The average crystal size is variable from 20 μm to 0.3 mm. The colour varies from dark violet-red to dark brownish-red and the streak is pale reddish-brown to pale purplish-brown. Crystals are translucent, brittle, vitreous, and do not fluoresce under ultraviolet light. The mineral shows neither twinning nor cleavage, has an uneven fracture, and the calculated density (for the empirical formula) is 4.904 g/cm3. Electron-microprobe analyses gave NiO 19.45, CoO 18.39, CuO 3.40, CaO 0.17, FeO 0.04, As2O5 60.32, total 101.77 wt.%. The empirical formula, derived from crystal-structure analysis and electron-microprobe analyses, is (Ni14.662+Co13.822+Cu2.412+Ca0.17Fe0.032+)Σ31.09(As1.975+O7)15, based on O = 105 atoms per formula unit (a.p.f.u.). In reflected plane-polarized light in air, petewilliamsite is dark grey with orange to spectral (multicoloured) internal reflections and no obvious bireflectance, anisotropy or pleochroism. Measured reflectance values in air are tabulated; the index of refraction calculated at 589 nm is 1.88. The mineral name honours Professor Peter (‘Pete’) Allan Williams of the University of Western Sydney, New South Wales, Australia, for his contributions to the study of secondary minerals.The crystal structure of petewilliamsite has been solved by direct methods and refined on the basis of F2 using 9212 unique reflections measured with Mo-Kα X-radiation on a diffractometer equipped with a CCDbased detector. The final R1 was 7.68%, calculated for 1273 observed reflections. The structure contains 15 symmetrically distinct As5+ cations, each of which is tetrahedrally coordinated by four O atoms, and pairs of these AsO4 tetrahedra share a vertex which results in As2O7 pyroarsenate groups that are in layers parallel to (010). The structure also has 16 distinct transition-metal M (M: Ni,Co) sites of which there are one tetrahedral, four square bipyramidal, and 11 octahedral arrangements. Adjacent pyroarsenate groups are linked through bonds to M cations. The structure of petewilliamsite is not closely related to other naturally occurring arsenates and it is the first pyroarsenate mineral.

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