Bariopharmacoalumite, a new mineral species from Cap Garonne, France and Mina Grande, Chile

2011 ◽  
Vol 75 (1) ◽  
pp. 135-144 ◽  
Author(s):  
S. J. Mills ◽  
M. S. Rumsey ◽  
G. Favreau ◽  
J. Spratt ◽  
M. Raudsepp ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Empirical Formula ◽  
Direct Methods ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
New Mineral Species ◽  
Crystal Unit Cell ◽  
Upper Estimate

AbstractBariopharmacoalumite, ideally Ba0.5Al4(AsO4)3(OH)4·4H2O, is a new mineral from Cap Garonne, France. It occurs in several places within the mine as colourless to pale yellow interpenetrating cubes up to 0.5 mm across. Bariopharmacoalumite is transparent to translucent, with a white streak, has an adamantine lustre and imperfect cleavage on {001}. The Vickers hardness is 234.35 and the Mohs harness is 3.5. Bariopharmacoalumite is isotropic, with n = 1.573 (upper estimate) [calculated from reflectance values at 589 nm using Fresnel Equations]. The empirical formula, based on 20 oxygen atoms, is: (Ba0.54Cu0.03K0.01)Σ0.58(Al3.99Fe0.02)Σ4.01(AsO4)3.00(OH)3.85O0.15·4H2O and the calculated density (on the basis of the empirical formula and single-crystal unit cell) is 2.580 g/cm3. The four strongest lines in the X-ray powder diffraction pattern are [dobs(Å), Iobs,(hkl)]: 7.759, 100, (001); 5.485, 27, (011); 3.878, 27, (002); 4.454, 18, (011). Bariopharmacoalumite from Cap Garonne is cubic, space group P4̄3m with a = 7.742(4) Å, V = 464.2(4) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.0705 for 215 reflections with I > 4σ(I) and is consistent with members of the pharmacosiderite supergroup. Data are also presented from zoned bariopharmacoalumite–bariopharmacosiderite crystals found at the Mina Grande mine, Chile.

Hydroniumpharmacosiderite, a new member of the pharmacosiderite supergroup from Cornwall, UK: structure and description

2010 ◽  
Vol 74 (5) ◽  
pp. 863-869 ◽  
Author(s):  
S. J. Mills ◽  
A. R. Kampf ◽  
P. A. Williams ◽  
P. Leverett ◽  
G. Poirier ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Empirical Formula ◽  
Direct Methods ◽  
Structure Type ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Mohs Hardness

AbstractHydroniumpharmacosiderite, ideally (H3O)Fe4(AsO4)3(OH)4·4H2O, is a new mineral from Cornwall, UK, probably from the St. Day group of mines. It occurs as a single yellowish green, slightly elongated cube, measuring 0.17 mm ×0.14 mm ×0.14 mm. The mineral is transparent with a vitreous lustre. It is brittle with a cleavage on {001}, has an irregular fracture, a white streak and a Mohs hardness of 2–3 (determined on H3O-exchanged pharmacosiderite). Hydroniumpharmacosiderite has a calculated density of 2.559 g cm–3 for the empirical formula. The empirical formula, based upon 20.5 oxygen atoms, is: [(H3O)0.50K0.48Na0.06]1.04(Fe3.79Al0.22)4.01[(As2.73P0.15)2.88O12](OH)4·4H2.14O. The five strongest lines in the X-ray powder diffraction pattern are [dobs(Å),Iobs,(hkl)]: 8.050,100,(001); 3.265,35,(112); 2.412,30,(113); 2.830,23,(202); 4.628,22,(111). Hydroniumpharmacosiderite is cubic, space group with a = 7.9587(2) Å, V = 504.11(2) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.0481 for 520 reflections with I > 2σ(I). The structure is consistent with determinations for H3O-exhchanged pharmacosiderite and the general pharmacosiderite structure type.

Oberthürite, Rh3(Ni,Fe)32S32 and torryweiserite, Rh5Ni10S16, two new platinum-group minerals from the Marathon deposit, Coldwell Complex, Ontario, Canada: Descriptions, crystal-chemical considerations, and comments on the geochemistry of rhodium

2021 ◽  
Vol 59 (6) ◽  
pp. 1833-1863
Author(s):  
Andrew M. McDonald ◽  
Ingrid M. Kjarsgaard ◽  
Louis J. Cabri ◽  
Kirk C. Ross ◽  
Doreen E. Ames ◽  
...  
Keyword(s):  
Crystal Structure ◽  
South Africa ◽  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Empirical Formula ◽  
Bushveld Complex ◽  
Calculated Density ◽  
X Ray ◽  
Platinum Group Minerals ◽  
Platinum Group

ABSTRACT Oberthürite, Rh3(Ni,Fe)32S32, and torryweiserite, Rh5Ni10S16, are two new platinum-group minerals discovered in a heavy-mineral concentrate from the Marathon deposit, Coldwell Complex, Ontario, Canada. Oberthürite is cubic, space group , with a 10.066(5) Å, V 1019.9(1) Å3, Z = 1. The six strongest lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 3.06(100)(311), 2.929(18)(222), 1.9518(39)(115,333), 1.7921(74)(440), 1.3184(15)(137,355) and 1.0312(30)(448). Associated minerals include: vysotskite, Au-Ag alloy, isoferroplatinum, Ge-bearing keithconnite, majakite, coldwellite, ferhodsite-series minerals (cuprorhodsite–ferhodsite), kotulskite, and mertieite-II, and the base-metal sulfides, chalcopyrite, bornite, millerite, and Rh-bearing pentlandite. Grains of oberthürite are up to 100 × 100 μm and the mineral commonly develops in larger composites with coldwellite, isoferroplatinum, zvyagintsevite, Rh-bearing pentlandite, and torryweiserite. The mineral is creamy brown compared to coldwellite and bornite, white when compared to torryweiserite, and gray when compared chalcopyrite and millerite. No streak or microhardness could be measured. The mineral shows no discernible pleochroism, bireflectance, or anisotropy. The reflectance values (%) in air for the standard COM wavelengths are: 36.2 (470 nm), 39.1 (546 nm), 40.5 (589 nm), and 42.3 (650 nm). The calculated density is 5.195 g/cm3, determined using the empirical formula and the unit-cell parameter from the refined crystal structure. The average result (n = 11) using energy-dispersive spectrometry is: Rh 10.22, Ni 38.83, Fe 16.54, Co 4.12, Cu 0.23 S 32.36, total 100.30 wt.%, which corresponds to (Rh2Ni0.67Fe0.33)Σ3.00(Ni19.30Fe9.09Co2.22Rh1.16Cu0.12)∑31.89S32.11, based on 67 apfu and crystallochemical considerations, or ideally, Rh3Ni32S32. The name is for Dr. Thomas Oberthür, a well-known researcher on alluvial platinum-group minerals, notably those found in deposits related to the Great Dyke (Zimbabwe) and the Bushveld complex (Republic of South Africa). Torryweiserite is rhombohedral, space group , with a 7.060(1), c 34.271(7) Å, V 1479.3(1), Z = 3. The six strongest lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 3.080(33)(021), 3.029(58)(116,0110), 1.9329(30)(036,1115,1210), 1.7797(100)(220,0216), 1.2512(49)(0416), and 1.0226(35)(060,2416,0232). Associated minerals are the same as for oberthürite. The mineral is slightly bluish compared to oberthürite, gray when compared to chalcopyrite, zvyagintsevite, and keithconnite, and pale creamy brown when compared to bornite and coldwellite. No streak or microhardness could be measured. The mineral shows no discernible pleochroism, bireflectance, or anisotropy. The reflectance values (%) in air for the standard COM wavelengths are: 34.7 (470 nm), 34.4 (546 nm), 33.8 (589 nm), and 33.8 (650 nm). The calculated density is 5.555 g/cm3, determined using the empirical formula and the unit-cell parameters from the refined crystal structure. The average result (n = 10) using wavelength-dispersive spectrometry is: Rh 28.02, Pt 2.56, Ir 1.98, Ru 0.10, Os 0.10, Ni 17.09, Fe 9.76, Cu 7.38, Co 1.77 S 30.97, total 99.73 wt.%, which corresponds to (Rh4.50Pt0.22Ir0.17Ni0.08Ru0.02Os0.01)∑5.00(Ni4.73Fe2.89Cu1.92Co0.50)Σ10.04S15.96, based on 31 apfu and crystallochemical considerations, or ideally Rh5Ni10S16. The name is for Dr. Thorolf (‘Torry') W. Weiser, a well-known researcher on platinum-group minerals, notably those found in deposits related to the Great Dyke (Zimbabwe) and the Bushveld complex (Republic of South Africa). Both minerals have crystal structures similar to those of pentlandite and related minerals: oberthürite has two metal sites that are split relative to that in pentlandite, and torryweiserite has a layered structure, comparable, but distinct, to that developed along [111] in pentlandite. Oberthürite and torryweiserite are thought to develop at ∼ 500 °C under conditions of moderate fS2, through ordering of Rh-Ni-S nanoparticles in precursor Rh-bearing pentlandite during cooling. The paragenetic sequence of the associated Rh-bearing minerals is: Rh-bearing pentlandite → oberthürite → torryweiserite → ferhodsite-series minerals, reflecting a relative increase in Rh concentration with time. The final step, involving the formation of rhodsite-series minerals, was driven via by the oxidation of Fe2+ → Fe3+ and subsequent preferential removal of Fe3+, similar to the process involved in the conversion of pentlandite to violarite. Summary comments are made on the occurrence and distribution of Rh, minerals known to have Rh-dominant chemistries, the potential existence of both Rh3+ and Rh2+, and the crystallochemical factors influencing accommodation of Rh in minerals.

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 > 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.

Shannonite, Pb2OCO3, a new mineral from the Grand Reef Mine, Graham County, Arizona, USA

1995 ◽  
Vol 59 (395) ◽  
pp. 305-310 ◽  
Author(s):  
A. C. Roberts ◽  
J. A. R. Stirling ◽  
G. J. C. Carpenter ◽  
A. J. Criddle ◽  
G. C. Jones ◽  
...  
Keyword(s):  
Empirical Formula ◽  
Short Wave ◽  
New Mineral ◽  
Orthorhombic Space Group ◽  
Weak Anisotropy ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
New Mineral Species ◽  
Transmission Electron

AbstractShannonite, ideally Pb2OCO3, is a new mineral species that occurs as mm-sized white porcellanous crusts, associated with fluorite, at the Grand Reef mine, Graham County, Arizona, USA. Other associated minerals are plumbojarosite, hematite, Mn-oxides, muscovite-2M1, quartz, litharge, massicot, hydrocerussite, minium, and unnamed PbCO3·2PbO. Shannonite is orthorhombic, space group P21221 or P212121, with unit-cell parameters (refined from X-ray powder data): a 9.294(3), b 9.000(3), c 5.133(2) Å, V 429.3(3) Å3, a:b:c 1.0327:1:0.5703, Z = 4. The strongest five lines in the X-ray powder pattern [d in Å (I)(hkl)] are: 4.02(40)(111); 3.215(100)(211); 3.181(90)(121); 2.858(40)(130); 2.564(35)(002). The average of eight electron microprobe analyses is PbO 89.9(5), CO2 (by CHN elemental analyser) 9.70, total 99.60 wt.%. With O = 4, the empirical formula is Pb1.91C1.05O4.00. The calculated density for the empirical formula is 7.31 and for the idealized formula is 7.59 g/cm3. In reflected light, shannonite is colourless-grey to white, with ubiquitous white internal reflections (× 16 objectives), weak anisotropy, barely detectable bireflectance, and no evidence of pleochroism. The calculated refractive index (at 590 nm) is 2.09. Measured reflectance values in air and in oil (× 4 objectives) are tabulated. Transmission electron-microscopy studies reveal that individual crystallites range in size from 10–400 nm, are platy, and are anhedral. Physical properties for cryptocrystalline crusts include: white streak; waxy lustre; opaque; nonfluorescent under both long- and short-wave ultraviolet light; uneven fracture; brittle; VHN100 97 (range 93–100); calculated Mohs’ hardness 3–3½. Shannonite is soluble in concentrated HCl and in dilute HNO3 and H2SO4. The mineral name is for David M. Shannon, who helped collect the samples and who initiated this study.

Description and crystal structure of a new mineral – plimerite, ZnFe3+4(PO4)3(OH)5 – the Zn-analogue of rockbridgeite and frondelite, from Broken Hill, New South Wales, Australia

2009 ◽  
Vol 73 (1) ◽  
pp. 131-148 ◽  
Author(s):  
P. Elliott ◽  
U. Kolitsch ◽  
G. Giester ◽  
E. Libowitzky ◽  
C. McCammon ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Empirical Formula ◽  
Direct Methods ◽  
Ore Deposits ◽  
New Mineral ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Broken Hill

Plimerite, ideally Zn (PO4)3(OH)5, is a new mineral from the Block 14 Opencut, Broken Hill, New SouthWales. It occurs as pale-green to dark-olive-green, almost black, acicular to prismatic and bladed crystals up to 0.5 mm long and as hemispherical aggregates of radiating acicular crystals up to 3 mm across. Crystals are elongated along [001] and the principal form observed is {100} with minor {010} and {001}. The mineral is associated with hinsdalite-plumbogummite, pyromorphite, libethenite, brochantite, malachite, tsumebite and strengite. Plimerite is translucent with a pale-greyish-green streak and a vitreous lustre. It shows an excellent cleavage parallel to {100} and {010} and distinct cleavage parallel to {001}. It is brittle, has an uneven fracture, a Mohs’ hardness of 3.5–4, D(meas.) = 3.67(5) g/cm3 and D(calc.) = 3.62 g/cm3 (for the empirical formula). Optically, it is biaxial negative with α = 1.756(5), β = 1.764(4), γ = 1.767(4) and 2V(calc.) of –63º; pleochroism is X pale-greenish-brown, Y pale-brown, Z pale-bluish-green; absorption Z > X > Y; optical orientation XYZ = cab. Plimerite is orthorhombic, space group Bbmm, unit-cell parameters: a = 13.865(3) Å, b = 16.798(3) Å, c = 5.151(10) Å, V = 1187.0(4) Å3 (single-crystal data) and Z = 4. Strongest lines in the X-ray powder diffraction pattern are [d (A˚ ), I, hkl]: 4.638, (50), (111); 3.388, (50), (041); 3.369, (55), (131); 3.168, (100), (132); 2.753, (60), (115); 2.575, (90), (200); 2.414, (75), (220); 2.400, (50), (221); 1.957, (40), (225). Electron microprobe analysis yielded (wt.%): PbO 0.36, CaO 0.17, ZnO 20.17, MnO 0.02, Fe2O3 29.82, FeO 2.98, Al2O3 4.48, P2O5 32.37, As2O5 0.09, H2O (calc) 6.84, total 97.30 (Fe3+/Fe2+ ratio determined by Mössbauer spectroscopy). The empirical formula calculated on the basis of 17 oxygens is Ca0.02Pb0.01Zn1.68Al0.60P3.09As0.01O17.00H5.15. The crystal structure was solved by direct methods and refined to an R1 index of 6.41% for 1332 observed reflections from single-crystal X-ray diffraction data (Mo-Kα radiation, CCD area detector). The structure of plimerite is isotypic with that of rockbridgeite and is based on face-sharing trimers of (Mϕ6) octahedra which link by sharing edges to form chains, that extend in the b-direction. Chains link to clusters comprising pairs of corner-sharing (Mϕ6) octahedra that link to PO4 tetrahedra forming sheets parallel to (001). The sheets link via octahedra and tetrahedra corners into a heteropolyhedral framework structure. The mineral name honours Professor Ian Plimer for his contributions to the study of the geology of ore deposits.

Agmantinite, Ag2MnSnS4, a new mineral with a wurtzite derivative structure from the Uchucchacua polymetallic deposit, Lima Department, Peru

2018 ◽  
Vol 83 (02) ◽  
pp. 233-238
Author(s):  
Frank N. Keutsch ◽  
Dan Topa ◽  
Rie Takagi Fredrickson ◽  
Emil Makovicky ◽  
Werner H. Paar
Keyword(s):  
Crystal Structure ◽  
Empirical Formula ◽  
New Mineral ◽  
Orthorhombic Space Group ◽  
Substitution Pattern ◽  
Calculated Density ◽  
X Ray ◽  
International Mineralogical Association ◽  
Cell Parameters ◽  
Polymetallic Deposit

AbstractAgmantinite, ideally Ag2MnSnS4, is a new mineral from the Uchucchacua polymetallic deposit, Oyon district, Catajambo, Lima Department, Peru. It occurs as orange–red crystals up to 100 μm across. Agmantinite is translucent with adamantine lustre and possesses a red streak. It is brittle. Neither fracture nor cleavage were observed. Based on the empirical formula the calculated density is 4.574 g/cm3. On the basis of chemically similar compounds the Mohs hardness is estimated at between 2 to 2½. In plane-polarised light agmantinite is white with red internal reflections. It is weakly bireflectant with no observable pleochroism with red internal reflections. Between crossed polars, agmantinite is weakly anisotropic with reddish brown to greenish grey rotation tints. The reflectances (RminandRmax) for the four standard wavelengths are: 19.7 and 22.0 (470 nm); 20.5 and 23.2 (546 nm); 21.7 and 2.49 (589 nm); and 20.6 and 23.6 (650 nm), respectively.Agmantinite is orthorhombic, space groupP21nm, with unit-cell parameters:a= 6.632(2),b= 6.922(2),c= 8.156(2) Å,V= 374.41(17) Å3,a:b:c0.958:1:1.178 andZ= 2. The crystal structure was refined toR= 0.0575 for 519 reflections withI >2σ(I). Agmantinite is the first known mineral of${M}_{\rm 2}^{\rm I} $MIIMIVS4type that is derived from wurtzite rather than sphalerite by ordered substitution of Zn, analogous to the substitution pattern for deriving stannite from sphalerite. The six strongest X-ray powder-diffraction lines derived from single-crystal X-ray diffraction data [din Å (intensity)] are: 3.51 (s), 3.32 (w), 3.11 (vs), 2.42 (w), 2.04 (m) and 1.88 (m). The empirical formula (based on 8 apfu) is (Ag1.94Cu0.03)Σ1.97(Mn0.98Zn0.05)Σ1.03Sn0.97S4.03.The crystal structure-derived formula is Ag2(Mn0.69Zn0.31)Σ1.00SnS4and the simplified formula is Ag2MnSnS4.The name is for the composition and the new mineral and mineral name have been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2014-083).

Oxyplumboroméite, Pb2Sb2O7, a new mineral species of the pyrochlore supergroup from Harstigen mine, Värmland, Sweden

2013 ◽  
Vol 77 (7) ◽  
pp. 2931-2939 ◽  
Author(s):  
U. Hålenius ◽  
F. Bosi
Keyword(s):  
Crystal Structure ◽  
Structure Refinement ◽  
New Mineral ◽  
Crystal Structure Refinement ◽  
Unit Cell Parameters ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
New Mineral Species ◽  
Mohs Hardness

AbstractOxyplumboroméite, Pb2Sb2O7, is a new mineral of the roméite group of the pyrochlore supergroup (IMA 2013-042). It is found together with calcite and leucophoenicite in fissure fillings in tephroite skarn at the Harstigen mine, Värmland, Sweden. The mineral occurs as yellow to brownish yellow rounded grains or imperfect octahedra. Oxyplumboroméite has a Mohs hardness of ∼5, a calculated density of 6.732 g/cm3 and is isotropic with a calculated refractive index of 2.061. Oxyplumboroméite is cubic, space group Fdm, with the unit-cell parameters a = 10.3783(6) Å, V = 1117.84(11) Å3 and Z = 8. The strongest five X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 2.9915(100)(222), 2.5928(32)(400), 1.8332(48)(440), 1.5638(38)(622) and 1.1900(12)(662). The crystal structure of oxyplumboroméite was refined to an R1 index of 3.02% using 160 unique reflections collected with MoKα radiation. Electron microprobe analyses in combination with crystal-structure refinement, infrared, Mössbauer and electronic absorption spectroscopy resulted in the empirical formula A(Pb0.92Ca0.87Mn0.09Sr0.01Na0.05)Σ1.93B(Sb1.73Fe3+0.27)Σ2.00X+Y[O6.64(OH)0.03]Σ6.67. Oxyplumboroméite is the Pb analogue of oxycalcioroméite, ideally Ca2Sb2O7.

Schlüterite-(Y), ideally (Y,REE)2Al(Si2O7)(OH)2F, a new mineral species from the Stetind pegmatite, Tysfjord, Nordland, Norway: description and crystal structure

2013 ◽  
Vol 77 (3) ◽  
pp. 353-366 ◽  
Author(s):  
M. A. Cooper ◽  
T. A. Husdal ◽  
N. A. Ball ◽  
Y. A. Abdu ◽  
F. C. Hawthorne
Keyword(s):  
Crystal Structure ◽  
Direct Methods ◽  
Crystal Structure Analysis ◽  
Mineral Species ◽  
New Mineral ◽  
Monoclinic Space Group ◽  
Silicate Mineral ◽  
Dominant Form ◽  
Calculated Density ◽  
New Mineral Species

AbstractSchlüterite-(Y), ideally (Y,REE)2Al(Si2O7)(OH)2F, is a new silicate mineral species from the Stetind pegmatite, Tysfjord, Nordland, Norway. It forms dense, fibrous, radiating aggregates (up to ∼2 mm) diverging to individual needle-like crystals (up to ∼1 mm long) in cavities. Crystals are acicular to bladed, flattened on {001} and elongated along [010], and the dominant form is {001}. Schlüterite-(Y) is transparent, pale pink with a white streak and a vitreous lustre, and does not fluoresce under short-wave ultraviolet light. Mohs hardness is 5½–6, and schlüterite-(Y) is brittle with an irregular fracture, and has no cleavage. The calculated density is 4.644 g/cm3. The indices of refraction are α = 1.755, β = 1.760, γ = 1.770, all ± 0.005, 2Vobs = 71.8 (5)°, 2Vcalc = 71°, non-pleochroic, optic orientation is X ˆ a = 83.1° (β obtuse), Y//b, Z ˆ c = 50.3° (β acute). Schlüterite-(Y) is monoclinic, space group P21/c, a 7.0722(2), b 5.6198(1), c 21.4390(4) Å, β 122.7756(3)°, V 716.43(5) Å3, Z = 4. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: [d (Å), I, (hkl)]: 4.769, 100, (012); 2.972, 55, (14); 3.289, 51, (112); 2.728, 49, (16); 2.810, 37, (020); 3.013, 37, ((16); 4.507, 36, (004). Chemical analysis by electron microprobe gave SiO2 22.64, Al2O3 9.45, Y2O3 15.35, La2O3 3.25, Ce2O3 9.69, Pr2O3 2.05, Nd2O3 9.50, Sm2O3 3.57, Gd2O3 4.65, Dy2O3 4.21, Er2O3 2.31, Yb2O3 1.86, F 2.71, H2Ocalc 3.78, O = F −1.14, sum 93.88 wt%. The H2O content was determined by crystal-structure analysis. On the basis of 10 anions with (OH) + F = 3 a.p.f.u. (atoms per formula unit), the empirical formula is (Y0.73Ce0.32Nd0.30Gd0.14Dy0.12La0.11Sm0.11Pr0.07Er0.06Yb0.05)Σ=2.01Al0.99Si2.01O7(OH)2.24F0.76. The crystal structure of schlüterite-(Y) was solved by direct methods and refined to an R1 index of 1.8% based on 1422 unique observed reflections. In the structure of schlüterite-(Y), Al(OH)4O2 octahedra share (OH)–(OH) edges to form [MΦ4] chains that are decorated by (Si2O7) groups that bridge O vertices of neighbouring octahedra in a staggered fashion on either side of the chain. These [Al(OH)2(Si2O7)] chains extend parallel to b, and are linked into a continuous framework via bonds to interstitial [8](Y,REE) (= <2.400 Å>) and [9](Y,REE) (= <2.548 Å>) atoms.

Fluorapophyllite-(NH4), NH4Ca4(Si8O20)F⋅8H2O, a new member of the apophyllite group from the Vechec quarry, eastern Slovakia

2020 ◽  
Vol 84 (4) ◽  
pp. 533-539
Author(s):  
Martin Števko ◽  
Jiří Sejkora ◽  
Jakub Plášil ◽  
Zdeněk Dolníček ◽  
Radek Škoda
Keyword(s):  
Crystal Structure ◽  
Brittle Fracture ◽  
Powder Diffraction ◽  
Slovak Republic ◽  
The Other ◽  
New Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Perfect Cleavage ◽  
Mohs Hardness

AbstractThe new mineral fluorapophyllite-(NH4), ideally NH4Ca4(Si8O20)F⋅8H2O, was found at the Vechec andesite quarry located near Vechec village, Vranov nad Topľou Co., Prešov Region, Slovak Republic. It occurs in cavities of quartz–illite–saponite–tobelite xenolith embedded in pyroxene andesite. Fluorapophyllite-(NH4) is associated with calcite, tridymite, pyrite, chabazite-Ca and heulandite-Ca. It forms clusters, aggregates or crystalline crusts consisting of individual, well-developed crystals up to 4 mm in size, exhibiting the forms {110}, {101} and {001}. The mineral is colourless to light pink and translucent with white streak and vitreous to pearly lustre; it is non-fluorescent under ultraviolet radiation. The Mohs hardness is ~4½ to 5, tenacity is brittle, fracture is irregular, and there is perfect cleavage on {001}. The calculated density is 2.325 g cm–3. Fluorapophyllite-(NH4) is optically uniaxial (+) with ω = 1.5414(5) and ɛ = 1.5393(8) (λ = 589 nm). It is non-pleochroic. The empirical formula (based on 29 O + F apfu) is [(NH4)0.55K0.32Na0.07Ca0.06]Σ1.00(Ca4.01Mg0.02)Σ4.03Si7.97O20[F0.84(OH)0.16]Σ1.00⋅8H2O. Fluorapophyllite-(NH4) is tetragonal, space group P4/mnc, a = 8.99336(9) Å, c = 15.7910(3) Å, V = 1277.18(3) Å3 and Z = 2. The seven strongest X-ray powder diffraction lines are [dobs in Å,(I,%)(hkl)]: 7.897(32)(002), 7.812(13)(101), 4.547(14)(103), 3.946(100)(004), 2.985(39)(105), 2.4841(11)(215) and 1.5788(12)(00.10). The crystal structure of fluorapophyllite-(NH4), refined to R1 = 0.0299 for 743 unique (I > 3σI) observed reflections, confirmed that the atomic arrangement is very similar to that of the other members of the apophyllite group. The new mineral is named according to the current nomenclature scheme for apophyllite-group minerals and is an NH4 dominant analogue of fluorapophyllite-(K), fluorapophyllite-(Na) and fluorapophyllite-(Cs).

Windmountainite, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, a new modulated, layered Fe3+-Mg-silicate-hydrate from Wind Mountain, New Mexico: Characterization and origin, with comments on the classification of palygorskite-group minerals

2020 ◽  
Vol 58 (4) ◽  
pp. 477-509
Author(s):  
Derek D. Leung ◽  
Andrew M. McDonald
Keyword(s):  
Crystal Structure ◽  
New Mexico ◽  
Late Stage ◽  
Structure Refinement ◽  
New Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
X Ray ◽  
New Mineral Species

ABSTRACT Windmountainite, ideally □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, is a new mineral species and member of the palygorskite group discovered as orange-brown, radiating aggregates that commonly fill vesicles (average 1.5 × 2.5 mm) within a phonolite dike at Wind Mountain, Otero County, New Mexico, USA. The mineral develops as tightly bound bundles (up to 0.02 × 6 mm) of acicular to bladed crystals that are elongate on [001] and flattened on the pinacoid {010}. Associated minerals include albite, aegirine, fluorapophyllite-(K), natrolite, neotocite, and montmorillonite, the last of these being observed to replace primary windmountainite. It has a dull luster, silky in aggregates, is translucent and has an orange-brown streak. It does not fluoresce under short-, medium-, or long-wave ultraviolet radiation. Windmountainite is brittle with a splintery fracture and has two good cleavages (predicted) on {110}, an estimated hardness of 2, a calculated density of 2.51 g/cm3, and a calculated navg of 1.593. A total of n = 30 EMPA (WDS) analyses from six grains yielded an average of (wt.%): Na2O 0.08, MgO 3.47, Al2O3 1.15, SiO2 49.76, Cl 0.07, K2O 0.40, CaO 0.68, TiO2 0.30, MnO 5.64, Fe2O3 20.17, H2O (calc.) 16.59, O=Cl –0.02, total 98.29. The empirical formula [based on Σ(T1, T2, M2, M3) = 12 cations pfu, excluding Ca, K, and Na] is: (□0.78Ca0.12K0.08Na0.02)Σ1.00(Fe3+1.93Al0.04Ti0.02)Σ1.99 (Mg0.81Mn2+0.75Fe3+0.44)Σ2.00□2(Si7.81Al0.17Ti0.01Fe3+0.01)Σ8.00O20[(OH)1.98Cl0.02]Σ2.00[(H2O)3.38(OH)0.62]Σ4.00·4H2O, yielding the simplified formula, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O. The predominance of Fe3+ is based on color, results from the crystal-structure refinement, the crystal-chemistry of palygorskite-group minerals, the association with Fe3+-dominant minerals, and considerations regarding the late-stage geochemical evolution of agpaitic rocks. The presence of H2O and OH was determined based on results from the refined crystal structure and Fourier-transform infrared spectroscopy. Windmountainite crystallizes in the space group C2/m with a 13.759(3), b 17.911(4), c 5.274(1) Å, β 106.44(3)°, V 1246.6(1) Å3, and Z = 2. The seven strongest powder X-ray diffraction lines are [d in Å (I), (hkl)]: 10.592 (100) (110), 5.453 (16) (130), 4.484 (19) (040), 4.173 (28) , 3.319 (53) (221, 400), 2.652 (30) , 2.530 (27) . The crystal structure was determined from single-crystal X-ray diffraction data and refined to R = 4.01% and wR2 = 10.70% using data from 902 reflections (Fo &gt; 4σFo). It is based on sheets of inverted double chains of SiO4 tetrahedra that sandwich ribbons of Mφ6 octahedra (φ = O, OH, H2O, Cl), giving rise to large channels (∼6.5 × 9 Å) that are occupied by loosely held H2O groups. A modified classification of the palygorskite group [general crystal-chemical formula M1M22M32M42T14T24O20(OH)2(H2O,OH)4·W] is proposed based on the occupants of the four M sites. Within this scheme, windmountainite is the □-Fe3+-Mg-□ member. The palygorskite group includes six members: palygorskite (monoclinic and orthorhombic polytypes), yofortierite, tuperssuatsiaite, raite, windhoekite, and windmountainite. Windmountainite is considered to have formed from late-stage fluids that were alkaline, oxidized, and rich in both Fe3+ and H2O; high aH2O conditions are reflective of abundant, hydrated feldspathoids (natrolite and analcime) forming as primary rock-forming minerals in the phonolite at Wind Mountain.

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