Hydroxykenopyrochlore, (□,Ce,Ba)2(Nb,Ti)2O6(OH,F), a New Member of the Pyrochlore Group from Araxá, Minas Gerais, Brazil

2021 ◽  
Author(s):  
Ritsuro Miyawaki ◽  
Koichi Momma ◽  
Satoshi Matsubara ◽  
Takashi Sano ◽  
Masako Shigeoka ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Empirical Formula ◽  
Minas Gerais ◽  
Powder Xrd ◽  
Lemon Yellow ◽  
Calculated Density ◽  
Xrd Pattern ◽  
Cell Parameters ◽  
Pyrochlore Group

ABSTRACT Hydroxykenopyrochlore, (□,Ce,Ba)2(Nb,Ti)2O6(OH,F), occurs in a weathered Nb-ore from alkaline-carbonatite complexes and pegmatites of the Brazilian shield mined by Compania Brasileira de Metalurgia e Mineração (CBMM), Araxá, Minas Gerais, Brazil. The mineral is a product of alkali metasomatism. It occurs as parts of granular grains up to 0.1 mm in size in association with Ba-bearing hydrokenopyrochlore. Hydroxykenopyrochlore is lemon yellow to yellow in color, non-fluorescent, and brittle. The hardness is 4½ on the Mohs scale. The calculated density is 4.36 g/cm3. It is cubic, Fd–3m, with cell parameters a 10.590(5) Å, V = 1187.6(10) Å3, and Z = 2. The strongest seven lines in the powder XRD pattern [d in Å (I/I0) hkl] are 6.06 (49) 111, 3.18 (27) 311, 3.05 (100) 222, 2.64 (29) 400, 1.870 (56) 440, 1.594 (50) 622, 1.213 (15) 662, and 1.182 (13) 840. The empirical formula derived from electron-microprobe analyses is [□1.117Ce0.532Nd0.035La0.021Pr0.010Sm0.003Y0.002Ba0.101Ca0.030Pb0.004Th0.061U0.007K0.040Na0.036]Σ2(Nb1.368Ti0.325P0.095Fe0.091Al0.082Zr0.039)Σ2[O4.719(OH)1.281]Σ6[(OH)0.846F0.154]. Hydroxykenopyrochlore is a member of the pyrochlore supergroup (class 4.DH.15 of Strunz & Nickel; class 8.2.1. of Dana). It is the vacancy-dominant analogue of hydroxycalciopyrochlore, (Ca,Na,U,□)2(Nb,Ti)2O6(OH), and the Nb-dominant analogue of hydroxykenomicrolite, (□,Na,Sb3+)2Ta2O6(OH), and of hydroxykenoelsmoreite, (□,Pb)2(W,Fe3+,Al)2(O,OH)6(OH).

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.

Minjiangite, BaBe2(PO4)2, a new mineral from Nanping No. 31 pegmatite, Fujian Province, southeastern China

2015 ◽  
Vol 79 (5) ◽  
pp. 1195-1202 ◽  
Author(s):  
C. Rao ◽  
F. Hatert ◽  
R. C. Wang ◽  
X. P. Gu ◽  
F. Dal Bo ◽  
...  
Keyword(s):  
Unit Cell ◽  
Powder Xrd ◽  
New Mineral ◽  
Unit Cell Parameters ◽  
Southeastern China ◽  
Fujian Province ◽  
Calculated Density ◽  
Xrd Pattern ◽  
Cell Parameters ◽  
New Mineral Species

AbstractMinjiangite, ideally BaBe2(PO4)2, is a new mineral species which has been found in the Nanping No. 31 pegmatite, Fujian Province, southeastern China. It occurs in the fractures of montebrasite from pegmatite zone IV, and is associated with quartz, muscovite, hydroxylapatite and palermoite. Minjiangite forms subhedral to euhedral white crystals from 5 to 200 μm long, transparent to translucent, with a vitreous lustre. The estimated Mohs hardness is ∼6, the tenacity is brittle and no cleavage was observed. The calculated density is 3.49 g/cm3. Optically, minjiangite is uniaxial (+), with ω = 1.587(3), ε = 1.602(2) (λ = 589 nm). Electron-microprobe analyses (average of 8) give P2O5 40.16, BaO 43.01, BeO 14.06 (measured by Secondary Ion Mass Spectrometry), SiO2 0.17, CaO 0.17, SrO 0.08, FeO 0.03, MgO 0.01, TiO2 0.07, K2O 0.05, Na2O 0.11, total 97.92 wt.%. The empirical formula, calculated on the basis of 8 O a.p.f.u., is (Ba0.99Ca0.01Na0.01)Σ1.01Be1.98(P1.99Si0.01)Σ2.00O8. The powder X-ray diffraction (XRD) pattern of minjiangite perfectly fits that of synthetic BaBe2(PO4)2; the strongest eight lines of the powder XRD pattern of the natural phosphate [d in Å (I)(hkl)] are: 3.763(100)(101); 2.836(81.3)(102); 2.515(32.3)(110); 2.178(25.6)(200); 2.1620(19)(103); 2.090(63.9)(201); 1.770(16.2)(113); 1.507(25.4)(212). Unit-cell parameters, refined from the powder XRD pattern of natural minjiangite, are a = 5.030(8), c = 7.467 (2) Å, V = 163.96(3) Å3. These unit-cell parameters confirm that minjiangite is the natural analogue of synthetic BaBe2(PO4)2(P6/mmm, a = 5.029(1), c = 7.466 (1) Å, V = 163.52(1) Å3, Z = 1); its crystal structure is topologically similar to that of dmisteinbergite, CaAl2Si2O8, a hexagonal polymorph of anorthite. The formation of minjiangite is related to the hydrothermal alteration of montebrasite by late Ba- and Be-rich fluids.

Oxycalciomicrolite, (Ca,Na)2(Ta,Nb,Ti)2O6(O,F), a new member of the microlite group (pyrochlore supergroup) from the Paleoproterozoic São João del Rei Pegmatite Province, Minas Gerais state, Brazil

2020 ◽  
pp. 1-5
Author(s):  
Victor H.R. Menezes da Silva ◽  
Ciro A. Ávila ◽  
Reiner Neumann ◽  
Fabiano R.L. Faulstich ◽  
Felipe E.A. Alves ◽  
...  
Keyword(s):  
Electron Microprobe ◽  
Minas Gerais ◽  
Accessory Mineral ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
Wavelength Dispersive Spectrometry ◽  
Minas Gerais State ◽  
Mohs Hardness

Abstract Oxycalciomicrolite (IMA2019-110), (Ca,Na)2(Ta,Nb,Ti)2O6(O,F), is a new member of microlite-group mineral found in the saprolite of the weathered Fumal pegmatite, located close to the city of Nazareno, Minas Gerais state, Brazil. It occurs as an accessory mineral associated with quartz, albite, microcline, muscovite, columbite-subgroup minerals, cassiterite, hematite, ilmenite, monazite-(Ce), xenotime-(Y), zircon, beryl, spinel, epidote and garnet-group minerals. Oxycalciomicrolite is found as octahedral crystals, occasionally modified to rhombododecahedra, ranging from 0.2 to 0.5 mm in size. The crystals are brownish-yellow to brownish-red and translucent, with white streak and vitreous to resinous lustre. The tenacity is brittle, with a Mohs hardness of 5–5½. Cleavage and parting are not observed; the fracture is conchoidal. Electron microprobe analysis, Raman and infrared spectroscopies and X-ray powder diffraction were applied to characterise this mineral. Oxycalciomicrolite is isotropic, ncalc. = 2.037, and the calculated density is 6.333 g/cm3. The composition is (Ca1.57□0.26Na0.06Sn0.03Sr0.03U0.02Mn0.02Fe0.01Ce0.01)∑2.00(Ta1.79Nb0.18Ti0.03)∑2.00O6.00[O0.64F0.19□0.17]∑1.00 analysed by electron microprobe using wavelength dispersive spectrometry. The unit-cell parameters obtained by Pawley fitting from powder X-ray diffraction data are a = 10.4325(4) Å and V = 1135.46(14) Å3 with Z = 8.

Layer stacking disorder in Mg-Fe chlorites based on powder X-ray diffraction data

2020 ◽  
Vol 105 (3) ◽  
pp. 353-362
Author(s):  
Katarzyna Luberda-Durnaś ◽  
Marek Szczerba ◽  
Małgorzata Lempart ◽  
Zuzanna Ciesielska ◽  
Arkadiusz Derkowski
Keyword(s):  
Accurate Determination ◽  
Unit Cell ◽  
Powder Xrd ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Xrd Pattern ◽  
X Ray ◽  
Cell Parameters ◽  
Layer Stacking

Abstract The primary aim of this study was the accurate determination of unit-cell parameters and description of disorder in chlorites with semi-random stacking using common X-ray diffraction (XRD) data for bulk powder samples. In the case of ordered chlorite structures, comprehensive crystallographic information can be obtained based on powder XRD data. Problems arise for samples with semi-random stacking, where due to strong broadening of hkl peaks with k ≠ 3n, the determination of unit-cell parameters is demanding. In this study a complete set of information about the stacking sequences in chlorite structures was determined based on XRD pattern simulation, which included determining a fraction of layers shifted by ±1/3b, interstratification with different polytypes and 2:1 layer rotations. A carefully selected series of pure Mg-Fe tri-trioctahedral chlorites with iron content in the range from 0.1 to 3.9 atoms per half formula unit cell was used in the study. In addition, powder XRD patterns were carefully investigated for the broadening of the odd-number basal reflections to determine interstratification of 14 and 7 Å layers. These type of interstratifications were finally not found in any of the samples. This result was also confirmed by the XRD pattern simulations, assuming interstratification with R0 ordering. Based on h0l XRD reflections, all the studied chlorites were found to be the IIbb polytype with a monoclinic-shaped unit cell (β ≈ 97°). For three samples, the hkl reflections with k ≠ 3n were partially resolvable; therefore, a conventional indexing procedure was applied. Two of the chlorites were found to have a monoclinic cell (with α, γ = 90°). Nevertheless, among all the samples, the more general triclinic (pseudomonoclinic) crystal system with symmetry C1 was assumed, to calculate unit-cell parameters using Le Bail fitting. A detailed study of semi-random stacking sequences shows that simple consideration of the proportion of IIb-2 and IIb-4/6 polytypes, assuming equal content of IIb-4 and IIb-6, is not sufficient to fully model the stacking structure in chlorites. Several, more general, possible models were therefore considered. In the first approach, a parameter describing a shift into one of the ±1/3b directions (thus, the proportion of IIb-4 and IIb-6 polytypes) was refined. In the second approach, for samples with slightly distinguishable hkl reflections with k ≠ 3n, some kind of segregation of individual polytypes (IIb-2/4/6) was considered. In the third approach, a model with rotations of 2:1 layers about 0°, 120°, 240° was shown to have the lowest number of parameters to be optimized and therefore give the most reliable fits. In all of the studied samples, interstratification of different polytypes was revealed with the fraction of polytypes being different than IIbb ranging from 5 to 19%, as confirmed by fitting of h0l XRD reflections.

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.

Kapellasite, Cu3Zn(OH)6CI2, a new mineral from Lavrion, Greece, and its crystal structure

2006 ◽  
Vol 70 (3) ◽  
pp. 329-340 ◽  
Author(s):  
W. Krause ◽  
H.-J. Bernhardt ◽  
R.S.W. Braithwaite ◽  
U. Kolitsch ◽  
R. Pritchard
Keyword(s):  
Crystal Structure ◽  
Electron Microprobe ◽  
Empirical Formula ◽  
New Mineral ◽  
Crystal Data ◽  
Secondary Mineral ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Pale Green ◽  
Light Green

AbstractKapellasite, Cu3Zn(OH)6Cl2, is a new secondary mineral from the Sounion No. 19 mine, Kamariza, Lavrion, Greece. It is a polymorph of herbertsmithite. Kapellasite forms crusts and small aggregates up to 0.5 mm, composed of bladed or needle-like indistinct crystals up to 0.2 mm long. The colour is green-blue, the streak is light green-blue. There is a good cleavage parallel to ﹛0001﹜. Kapellasite is uniaxial negative, ω = 1.80(1), ε = 1.76(1); pleochroism is distinct, with E = pale green, O = green-blue. Dmeas = 3.55(10) g/cm3; Dcalc. = 3.62 g/cm3. Electron microprobe analyses of the type material gave CuO 58.86, ZnO 13.92, NiO 0.03, CoO 0.03, Fe2O3 0.04, Cl 16.70, H2O (calc.) 12.22, total 101.80, less O = Cl 3.77, total 98.03 wt.%. The empirical formula is (Cu3.24Zn0.75)Σ3.99(OH)5.94Cl2.06, based on 8 anions. The five strongest XRD lines are [d in Å (I/I0, hkl)] 5.730 (100, 001), 2.865 (11, 002), 2.730 (4, 200), 2.464 (9, 021/201), 1.976 (5, 022/202). Kapellasite is trigonal, space group Pml, unit-cell parameters (from single-crystal data) a = 6.300(1), c = 5.733(1) Å, V= 197.06(6) Å3, Z = 1. The crystal structure of kapellasite is based on brucite-like sheets parallel to (0001), built from edge-sharing distorted M(OH,Cl)6 (M = Cu, Zn) octahedra. The sheets stack directly on each other (…AAA… stacking). Bonding between adjacent sheets is only due to weak hydrogen and O…C1 bonds. The name is in honour of Christo Kapellas (1938–2004), collector and mineral dealer from Kamariza, Lavrion, Greece.

Barikaite, Pb10Ag3(Sb8As11)Σ19S40, a new member of the sartorite homologous series

2013 ◽  
Vol 77 (7) ◽  
pp. 3039-3046 ◽  
Author(s):  
D. Topa ◽  
E. Makovicky ◽  
H. Tajedin ◽  
H. Putz ◽  
G. Zagler
Keyword(s):  
Homologous Series ◽  
Empirical Formula ◽  
Mean Value ◽  
Crystal Structure Analysis ◽  
New Mineral ◽  
Calculated Density ◽  
Cell Parameters ◽  
New Mineral Species ◽  
Reflected Light ◽  
Mohs Hardness

AbstractBarikaite, ideally Pb10Ag3(Sb8As11)Σ19S40, is a new mineral species from the Barika Au-Ag deposit, Azarbaijan Province, western Iran. It was formed in fractures developed in silica bands situated in massive banded pyrite and baryte ores. These fractures house veinlets that contain a number of Ag-As-Sb-Pb-rich sulfosalts, tetrahedrite-tennantite, realgar, pyrite and electrum. Barikaite appears as inclusions in guettardite. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light barikaite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, in air) are: 37.0, 39.3 at 470 nm, 34.1, 36.9 at 546 nm, 33.1, 36.2 at 589 nm and 31.3, 34.1 at 650 nm. The Mohs hardness is 3–3½, microhardness VHN50 exhibits the range 192 – 212, with a mean value of 200 kg mm–2. The average results of five electron-microprobe analyses in a grain are (in wt.%): Pb 35.77(33), Ag 5.8(1), Tl 0.15(08), Sb 18.33(09), As 15.64(16), S 24.00(15), total 99.69(10) wt.%, corresponding to Pb9.31Ag2.90Tl0.04(Sb8.12As11.26)Σ19.36S40.37 (on the basis of 32Me + 40S = 72 a.p.f.u.). The simplified formula, Pb10Ag3(Sb8As11)Σ19S40, is in accordance with the results of a crystal-structure analysis, and requires Pb 37.89, Ag 5.91, Sb 17.79, As 15.05 and S 23.42 (wt.%). The variation of chemical composition is minor, the empirical formula ranging from Pb10.39Ag2.32Tl0.02Sb7.52As11.27S40.49 to Pb9.24Ag2.93Tl0.04Sb8.13As11.35S40.31. Barikaite has monoclinic symmetry, space group P21/n and unit-cell parameters a 8.5325(7) Å, b 8.0749(7) Å, c 24.828(2) Å, and b 99.077(6)o, Z = 1. Calculated density for the empirical formula is 5.34 (g cm–3). The strongest eight lines in the (calculated) powder-diffraction pattern [d in Å(I)(hkl)] are: 3.835(63)(022), 3.646(100)(016), 3.441(60)(212), 3.408(62)(14), 2.972(66)(16), 2.769(91)(222), 2.752(78)(24) and 2.133(54)(402). Barikaite is the N = 4 member of the sartorite homologous series with a near-equal role of As and Sb, which have an ordered distribution pattern in the structure. It is a close homeotype of rathite and more distantly related to dufrénoysite (both distinct, pure arsenian N = 4 members) and it completes the spectrum of Sb-rich members of the sartorite homologous series. The new mineral and its name have been approved by the IMA-CNMNC (IMA 2012-055).

scholarly journals Fluorlamprophyllite, Na3(SrNa)Ti3(Si2O7)2O2F2, a new mineral from Poços de Caldas alkaline massif, Morro do Serrote, Minas Gerais, Brazil

2018 ◽  
Vol 82 (1) ◽  
pp. 121-131 ◽  
Author(s):  
Marcelo B. Andrade ◽  
Hexiong Yang ◽  
Robert T. Downs ◽  
Gunnar Färber ◽  
Reynaldo R. Contreira Filho ◽  
...  
Keyword(s):  
Layered Silicate ◽  
Minas Gerais ◽  
New Mineral ◽  
Chemical Formula ◽  
Calculated Density ◽  
Cell Parameters ◽  
New Mineral Species ◽  
Poços De Caldas ◽  
Mohs Hardness ◽  
Alkaline Massif

ABSTRACTA new mineral species, fluorlamprophyllite (IMA2013-102), ideally Na3(SrNa)Ti3(Si2O7)2O2F2, has been found in the Poços de Caldas alkaline massif, Morro do Serrote, Minas Gerais, Brazil. Alternatively, the idealized chemical formula could be written as (SrNa)[(Na3Ti)F2][Ti2(Si2O7)2O2], setting the large interlayer cations before the cations of the layer. Fluorlamprophyllite is the F-analogue of lamprophyllite. It is associated with aegirine, analcime, natrolite, nepheline and microcline. Fluorlamprophyllite crystals are brownish-orange and bladed. The mineral is transparent with a pale yellow streak and an adamantine lustre. It is brittle and has a Mohs hardness of ~3; cleavage is perfect on {100} and no parting was observed. The calculated density is 3.484 g/cm3. Optically, fluorlamprophyllite is biaxial (+), with α = 1.735(7), β = 1.749(7) and γ = 1.775(9) and 2Vmeas = 72(3)°. An electron microprobe analysis produced an average composition (wt.%) (9 points) of Na2O 10.63(30), K2O 0.47(3), SiO2 30.51(13), SrO 18.30(24), MgO 0.81(17), Al2O3 0.23(2), CaO 1.11(7), MnO 5.03(38), TiO2 27.41(87), Fe2O3 2.45(37), F 2.86(23), plus H2O 1.00 (added to bring the total close to 100%), –O = F –1.20, with the total = 98.61%. The elements Nb and Ba were sought, but contents were below microprobe detection limits. The resultant chemical formula was calculated on the basis of 18 (O + F) atoms per formula unit. The addition of 1.00 wt.% H2O brought [F+(OH)] = 2 pfu, yielding (Na2.63Sr1.35Mn0.54Ca0.15Mg0.15K0.08)Σ4.90(Ti2.63Fe0.24Al0.04)Σ2.91Si3.89O16[F1.15(OH)0.85]Σ2.00. The mineral is monoclinic, with space group C2/m and unit-cell parameters a = 19.255(2), b = 7.0715(7), c = 5.3807(6) Å, β = 96.794(2)° and V = 727.5(1) Å3. The structure is a layered silicate inasmuch as the O atoms are arranged in well-defined, though not necessarily close-packed layers.

scholarly journals Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

2017 ◽  
Vol 81 (3) ◽  
pp. 555-564 ◽  
Author(s):  
M. B. Andrade ◽  
H. Yang ◽  
D. Atencio ◽  
R. T. Downs ◽  
N. V. Chukanov ◽  
...  
Keyword(s):  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Minas Gerais ◽  
Calculated Density ◽  
Group Mineral ◽  
Cell Parameters ◽  
Mohs Hardness ◽  
Long Range Ordering ◽  
Symmetry Space ◽  
Symmetry Space Group

AbstractHydroxycalciomicrolite, Ca1.5Ta2O6(OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to1.5 mm in size. The crystals are yellow and translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5–6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm–3. Hydroxycalciomicroliteis isotropic,ncalc.= 2.010. The infrared and Raman spectra exhibit bands due to O–H stretching vibrations. The chemical composition determined from electron microprobe analysis (n= 13) is (wt.%): Na2O 0.36(8), CaO 15.64(13), SnO20.26(3),Nb2O52.82(30), Ta2O578.39(22), MnO 0.12(2), F 0.72(12) and H2O 1.30 (from the crystal structure data), O = F –0.30, total 99.31(32), yielding an empirical formula, (Ca1.48Na0.06Mn0.01)∑1.55(Ta1.88Nb0.11Sn0.01)∑2.00O6.00[(OH)0.76F0.20O0.04].Hydroxycalciomicrolite is cubic, with unit-cell parametersa= 10.4205(1) Å,V= 1131.53(2) Å3andZ= 8. It represents a pyrochlore supergroup, microlite-group mineral exhibitingP4332 symmetry, instead ofFd3m. Thereduction in symmetry is due to long-range ordering of Ca and vacancies on theAsites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species withP4332or lower-symmetry space group can be discovered and characterized.

Waimirite-(Y), orthorhombic YF3, a new mineral from the Pitinga mine, Presidente Figueiredo, Amazonas, Brazil and from Jabal Tawlah, Saudi Arabia: description and crystal structure

2015 ◽  
Vol 79 (3) ◽  
pp. 767-780 ◽  
Author(s):  
Daniel Atencio ◽  
Artur C. Bastos Neto ◽  
Vitor P. Pereira ◽  
José T. M. M. Ferron ◽  
M. Hoshino ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Saudi Arabia ◽  
Single Crystal ◽  
Electron Microprobe ◽  
Empirical Formula ◽  
Unit Cell ◽  
New Mineral ◽  
Charge Balance ◽  
Unit Cell Parameters ◽  
Cell Parameters

AbstractWaimirite-(Y) (IMA 2013-108), orthorhombic YF3, occurs associated with halloysite, in hydrothermal veins (up to 30 mm thick) cross-cutting the albite-enriched facies of the A-type Madeira granite (∼1820 Ma), at the Pitinga mine, Presidente Figueiredo Co., Amazonas State, Brazil. Minerals in the granite are 'K-feldspar', albite, quartz, riebeckite, 'biotite', muscovite, cryolite, zircon, polylithionite, cassiterite, pyrochlore-group minerals, 'columbite', thorite, native lead, hematite, galena, fluorite, xenotime-(Y), gagarinite-(Y), fluocerite-(Ce), genthelvite–helvite, topaz, 'illite', kaolinite and 'chlorite'. The mineral occurs as massive aggregates of platy crystals up to ∼1 μm in size. Forms are not determined, but synthetic YF3 displays pinacoids, prisms and bipyramids. Colour: pale pink. Streak: white. Lustre: non-metallic. Transparent to translucent. Density (calc.) = 5.586 g/cm3 using the empirical formula. Waimirite-(Y) is biaxial, mean n = 1.54–1.56. The chemical composition is (average of 24 wavelength dispersive spectroscopy mode electron microprobe analyses, O calculated for charge balance): F 29.27, Ca 0.83, Y 37.25, La 0.19, Ce 0.30, Pr 0.15, Nd 0.65, Sm 0.74, Gd 1.86, Tb 0.78, Dy 8.06, Ho 1.85, Er 6.38, Tm 1.00, Yb 5.52, Lu 0.65, O (2.05), total (97.53) wt.%. The empirical formula (based on 1 cation) is (Y0.69Dy0.08Er0.06Yb0.05Ca0.03Gd0.02Ho0.02Nd0.01Sm0.01Tb0.01Tm0.01Lu0.01)Σ1.00[F2.54〈0.25O0.21]Σ3.00. Orthorhombic, Pnma, a = 6.386(1), b = 6.877(1), c = 4.401(1) Å, V = 193.28(7) Å3, Z = 4 (powder data). Powder X-ray diffraction (XRD) data [d in Å (I) (hkl)]: 3.707 (26) (011), 3.623 (78) (101), 3.438 (99) (020), 3.205 (100) (111), 2.894 (59) (210), 1.937 (33) (131), 1.916 (24) (301), 1.862 (27) (230). The name is for the Waimiri-Atroari Indian people of Roraima and Amazonas. A second occurrence of waimirite-(Y) is described from the hydrothermally altered quartz-rich microgranite at Jabal Tawlah, Saudi Arabia. Electron microprobe analyses gave the empirical formula (Y0.79Dy0.08Er0.05Gd0.03Ho0.02Tb0.01Tm0.01Yb0.01)Σ1.00[F2.85O0.08〈0.07]Σ3.00. The crystal structure was determined with a single crystal from Saudi Arabia. Unit-cell parameters refined from single-crystal XRD data are a = 6.38270(12), b = 6.86727(12), c = 4.39168(8) Å, V = 192.495(6) Å3, Z = 4. The refinement converged to R1 = 0.0173 and wR2 = 0.0388 for 193 independent reflections. Waimirite-(Y) is isomorphous with synthetic SmF3, HoF3 and YbF3. The Y atom forms a 9-coordinated YF9 tricapped trigonal prism in the crystal structure. The substitution of Y for Dy, as well as for other lanthanoids, causes no notable deviations in the crystallographic values, such as unit-cell parameters and interatomic distances, from those of pure YF3.

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