Daniel Atencio

Clarification of status of species in the pyrochlore supergroup

Abstract After careful consideration of the semantics of status categories for mineral species names, minor corrections and disambiguations are presented for a recent report on the nomenclature of the pyrochlore supergroup. The names betafite, elsmoreite, microlite, pyrochlore and roméite are allocated as group names within the pyrochlore supergroup. The status of the names bindheimite, bismutostibiconite, jixianite, monimolite, partzite, stetefeldtite and stibiconite is changed from ‘discredited’ to ‘questionable’ pending further research.

Menezesite, the first natural heteropolyniobate, from Cajati, São Paulo, Brazil: Description and crystal structure

Abstract Menezesite, ideally Ba2MgZr4(BaNb12O42)·12H2O, occurs as a vug mineral in the contact zone between dolomite carbonatite and “jacupirangite” (=a pyroxenite) at the Jacupiranga mine, in Cajati county, São Paulo state, Brazil, associated with dolomite, calcite, magnetite, clinohumite, phlogopite, ancylite-(Ce), strontianite, pyrite, and tochilinite. This is also the type locality for quintinite-2H. The mineral forms rhombododecahedra up to 1 mm, isolated or in aggregates. Menezesite is transparent and displays a vitreous luster; it is reddish brown with a white streak. It is non-fluorescent. Mohs hardness is about 4. Calculated density derived from the empirical formula is 4.181 g/cm3. It is isotropic, nmeas > 1.93(1) (white light); ncalc = 2.034. Menezesite exhibits weak anomalous birefringence. The empirical formula is (Ba1.47K0.53Ca0.31Ce0.17Nd0.10Na0.06La0.02)Σ2.66(Mg0.94Mn0. 23Fe0.23Al0.03)Σ1.43(Zr2.75Ti0.96Th0.29)Σ4.00 [(Ba0.72Th0.26U0.02)Σ1.00(Nb9.23Ti2.29Ta0.36Si0.12)Σ12.00O42]·12H2O. The mineral is cubic, space group Im3̅ (204), a = 13.017(1) Å, V = 2206(1) Å3, Z = 2. Menezesite is isostructural with the synthetic compound Mg7[MgW12O42](OH)4·8H2O. The mineral was named in honor of Luiz Alberto Dias Menezes Filho (born 1950), mining engineer, mineral collector and merchant. Both the description and the name were approved by the CNMMN-IMA (Nomenclature Proposal 2005-023). Menezesite is the first natural heteropolyniobate. Heteropolyanions have been employed in a range of applications that include virus-binding inorganic drugs (including the AIDs virus), homogeneous and heterogeneous catalysts, electro-optic and electrochromic materials, metal and protein binding, and as building blocks for nanostructuring of materials.

Coutinhoite, a new thorium uranyl silicate hydrate, from Urucum mine, Galiléia, Minas Gerais, Brazil

Abstract The new mineral coutinhoite, ideally ThxBa(1-2x)(H2O)y(UO2)2Si5O13⋅H2O, with 0 ≤ x ≤ 0.5 and 0 ≤ y ≤ (2 + x), occurs as a secondary hydrothermal mineral in the Córrego do Urucum granitic pegmatite, Lavra Urucum, Galiléia Co., Minas Gerais, Brazil. Coutinhoite is intimately associated with weeksite, phosphuranylite, meta-uranocircite, and uranocircite on muscovite and microcline. The mineral forms irregular aggregates with very small curved scales, flaky crystals, up to 10 μm long and with a thickness up to about 0.5 μm. Coutinhoite is transparent to translucent and displays a waxy to silky luster; color and streak are yellow. It is non-fluorescent. The hardness is less than 2. It is brittle. Calculated density is 3.839 g/cm3. Coutinhoite is biaxial negative, α 1.620(3), β 1.627(3), γ 1.629(3), 2Vmeas. = 40(5)°, 2Vcalc. = 56.1°, dispersion r < v strong, orientation Y = c. Pleochroism is Z > Y, X yellow. The empirical formula (based on Si + P = 5) is (Th0.30Ba0.19K0.07Ca0.04)Σ0.60(UO2)2.00(Si4.92P0.08)Σ5.00O12.91·2.86H2O. The mineral is orthorhombic, probable space group Cmmb (67). Cell parameters were refined from the powder data: a 14.1676(9), b 14.1935(9), c 35.754(2) Å, V = 7189.7(2) Å3, and Z = 16. It is probably isostructural with weeksite. Both the description and name were approved by the CNMMN-IMA (Nomenclature Proposal 2003-025).

Footemineite, the Mn-analog of atencioite, from the Foote mine, Kings Mountain, Cleveland County, North Carolina, U.S.A., and its relationship with other roscherite-group minerals

Abstract Footemineite, ideally Ca2Mn2+□Mn22+Mn22+Be4(PO4)6(OH)4·6H2O, triclinic, is a new member of the roscherite group. It occurs on thin fractures crossing quartz-microcline-spodumene pegmatite at the Foote mine, Kings Mountain, Cleveland County, North Carolina, U.S.A. Associated minerals are albite, analcime, eosphorite, siderite/rhodochrosite, fairfieldite, fluorapatite, quartz, milarite, and pyrite. Footemineite forms prismatic to bladed generally rough to barrel-shaped crystals up to about 1.5 mm long and 1 mm in diameter. Its color is yellow, the streak is white, and the luster is vitreous to slightly pearly. Footemineite is transparent and non-fluorescent. Twinning is simple, by reflection, with twin boundaries across the length of the crystals. Cleavage is good on {01̅1} and {100}. Density (calc.) is 2.873 g/cm3. Footemineite is biaxial (-), nα = 1.620(2), nβ = 1.627(2), nγ = 1.634(2) (white light). 2Vobs = 80°, 2Vcalc = 89.6°. Orientation: X ^ b ~ 12°, Y ^ c ~ 15°, Z ^ a ~ 15°. Elongation direction is c, dispersion: r > v or r < v, weak. Pleochroism: β (brownish yellow) > α = γ (yellow). Mössbauer and IR spectra are given. The chemical composition is (EDS mode electron microprobe, Li and Be by ICP-OES, Fe3+:Fe2+ by Mössbauer, H2O by TG data, wt%): Li2O 0.23, BeO 9.54, CaO 9.43, SrO 0.23, BaO 0.24, MgO 0.18, MnO 26.16, FeO 2.77, Fe2O3 0.62, Al2O3 0.14, P2O5 36.58, SiO2 0.42, H2O 13.1, total 99.64. The empirical formula is (Ca1.89Sr0.03Ba0.02)Σ1.94(Mn2+0.90□0.10)Σ1.00(□0.78Li0.17Mg0.05)Σ1.00(Mn2+3.25Fe2+0.43Fe3+0.09 Al0.03)Σ3.80Be4.30(P5.81Si0.08O24)[(OH)3.64(H2O)0.36]Σ4.00·6.00H2O. The strongest reflection peaks of the powder diffraction pattern [d, Å (I, %) (hkl)] are 9.575 (53) (010), 5.998 (100) (01̅1), 4.848 (26) (021), 3.192 (44) (210), 3.003 (14) (02̅2), 2.803 (38) (1̅03), 2.650 (29) (2̅02), 2.424 (14) (231). Single-crystal unit-cell parameters are a = 6.788(2), b = 9.972(3), c = 10.014(2) Å, α = 73.84(2), β = 85.34(2), γ = 87.44(2)°; V = 648.74 Å3, Z = 1. The space group is P1̅. Crystal structure was refined to R = 0.0347 with 1273 independent reflections (F > 2σ). Footemineite is dimorphous with roscherite, and isostructural with atencioite. It is identical with the mineral from Foote mine described as “triclinic roscherite.” The name is for the Foote mine, type locality for this and several other minerals.

Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, from Eduardo mine, Conselheiro Pena, Minas Gerais, Brazil: Second arsenate in the laueite mineral group

Abstract Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1-2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm3. The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition (n = 4, WDS, calculated for the condition Fe2+:Fe3+ = 1:2, H2O for the ideal structural formula, wt%) is: FeO 11.50, Fe2O3 25.56, CaO 15.41, As2O5 33.51, H2O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe2+0.98Fe3+1.96[(AsO4)1.79(PO4)0.31](OH)1.52·8.08H2O. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(1̅21), 3.158(32)(13̅0), 2.960(39)(022̅), 2.884(35)(1̅31), 2.680(29)(2̅11), and 2.540(23)(2̅10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P1̅) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), γ = 102.30(2)°, V = 347.1(2) Å3, and Z = 1. Gladstone-Dale compatibility is -0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.

Bendadaite, a new iron arsenate mineral of the arthurite group

Abstract Bendadaite, ideally Fe2+Fe23+(AsO4)2(OH)2·4H2O, is a new member of the arthurite group. It was found as a weathering product of arsenopyrite on a single hand specimen from the phosphate pegmatite Bendada, central Portugal (type locality). Co-type locality is the granite pegmatite of Lavra do Almerindo (Almerindo mine), Linópolis, Divino das Laranjeiras county, Minas Gerais, Brazil. Further localities are the Veta Negra mine, Copiapó province, Chile; Oumlil-East, Bou Azzer district, Morocco; and Pira Inferida yard, Fenugu Sibiri mine, Gonnosfanadiga, Medio Campidano Province, Sardinia, Italy. Type bendadaite occurs as blackish green to dark brownish tufts (<0.1 mm long) and flattened radiating aggregates, in intimate association with an intermediate member of the scorodite-mansfieldite series. It is monoclinic, space group P21/c, with a = 10.239(3) Å, b = 9.713(2) Å, c = 5.552(2) Å, β = 94.11(2)º, V = 550.7(2) Å3, Z = 2. Electron-microprobe analysis yielded (wt.%): CaO 0.04, MnO 0.03, CuO 0.06, ZnO 0.04, Fe2O3 (total) 43.92, Al2O3 1.15, SnO2 0.10, As2O5 43.27, P2O5 1.86, SO3 0.03. The empirical formula is (Fe0.522+Fe0.323+⃞0.16)∑1.00(Fe1.893+Al0.11)∑2.00(As1.87P0.13)∑2.00O8(OH)2.00·4H2O, based on 2(As,P) and assuming ideal 8O, 2(OH), 4H2O and complete occupancy of the ferric iron site by Fe3+ and Al. Optically, bendadaite is biaxial, positive, 2Vest. = 85±4º, 2Vcalc. = 88º, with α 1.734(3), β 1.759(3), γ 1.787(4). Pleochroism is medium strong: X pale reddish brown, Y yellowish brown, Z dark yellowish brown; absorption Z > Y > X, optical dispersion weak, r > v. Optical axis plane is parallel to (010), with X approximately parallel to a and Z nearly parallel to c. Bendadaite has vitreous to sub-adamantine luster, is translucent and non-fluorescent. It is brittle, shows irregular fracture and a good cleavage parallel to {010}. Dmeas. 3.15±0.10 g/cm3, Dcalc. 3.193 g/cm3 (for the empirical formula). The five strongest powder diffraction lines [d in Å (I)(hkl)] are 10.22 (10)(100), 7.036 (8)(110), 4.250 (5)(111), 2.865 (4)(3̄11), 4.833 (3)(020,011). The d spacings are very similar to those of its Zn analogue, ojuelaite. The crystal structure of bendadaite was solved and refined using a crystal from the co-type locality with the composition (Fe0.952+⃞0.05)∑1.00(Fe1.803+Al0.20)∑2.00(As1.48P0.52)∑2.00O8(OH)2·4H2O (R = 1.6%), and confirms an arthurite-type atomic arrangement.

The crystal structure of lewisite, (Ca,Sb3+,Fe3+,Al,Na,Mn,□)2(Sb5+,Ti)2O6(OH)

Abstract The crystal structure of lewisite, ideally (Ca,Sb 3+ ,Fe 3+ ,Al,Na,Mn,□) 2 (Sb 5+ ,Ti) 2 O 6 (OH), cubic, space group Fd3m , a =10.311(7) A, V =1096.23 A 3 , Z =8, d calc. =4.73, d obs. =4.95 g/cm 3 , F (000)=1531, has been solved by single-crystal X-ray diffraction analysis and refined to R =0.015 for 218 unique reflections with ∣ F ∣>4 σ ( F ). The pyrochlore-like structure contains distorted A cubes and B octahedra. A comparison among lewisite and several other pyrochlore-like structures with B=Sb 5+ shows that increase of the unit cell parameter depends on the size of the A-cations. XRD study of lewisite did not reveal the intergrowth of two sublattices, previously anticipated in this structure. A comparison of two models with a static distribution of Sb 3+ (splitting of the A site) and a dynamic distribution (anharmonic thermal displacements of cations in the A site) led us to prefer the latter. A structural study of romeite is now necessary to establish the identity of lewisite and romeite.

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

Abstract Waimirite-(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)∑1.00[F2.54⃞0.25O0.21]∑3.00. 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 (Y0.79Dy0.08Er0.05Gd0.03Ho0.02Tb0.01 Tm0.01Yb0.01)∑1.00[F2.85O0.08⃞0.07]∑3.00. 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.

Fluorcalciomicrolite, (Ca,Na,□)2Ta2O6F, a new microlite-group mineral from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

Abstract Fluorcalciomicrolite, (Ca,Na,⃞)2Ta2O6F, is a new microlite-group, pyrochlore supergroup mineral approved by the CNMNC (IMA 2012-036). It occurs as an accessory mineral in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. Associated minerals include: microcline, albite, quartz, muscovite, spodumene, ‘‘lepidolite’’, cassiterite, tantalite-(Mn), monazite-(Ce), fluorite, ‘‘apatite’’, beryl, ‘‘garnet’’, epidote, magnetite, gahnite, zircon, ‘‘tourmaline’’, bityite, hydrokenomicrolite, and other microlite-group minerals under study. Fluorcalciomicrolite occurs as euhedral, untwinned, octahedral crystals 0.1-1.5 mm in size, occasionally modified by rhombododecahedral faces. The crystals are colourless and translucent; the streak is white, and the lustre is adamantine to resinous. It does not fluoresce under ultraviolet light. Mohs’ hardness is 4½-5, tenacity is brittle. Cleavage is not observed; fracture is conchoidal. The calculated density is 6.160 g/cm3. The mineral is isotropic, ncalc. = 1.992. The Raman spectrum is dominated by bands of B-X octahedral bond stretching and X-B-X bending modes. The chemical composition (n = 6) is (by wavelength dispersive spectroscopy, H2O calculated to obtain charge balance, wt.%): Na2O 4.68, CaO 11.24, MnO 0.01, SrO 0.04, BaO 0.02, SnO2 0.63, UO2 0.02, Nb2O5 3.47, Ta2O5 76.02, F 2.80, H2O 0.48, O=F -1.18, total 98.23. The empirical formula, based on 2 cations at the B site, is (Ca1.07Na0.81⃞0.12)∑2.00(Ta1.84Nb0.14Sn0.02)∑2.00[O5.93(OH)0.07]6.00[F0.79(OH)0.21]. The strongest eight X-ray powder-diffraction lines [d in Å (I)(hkl)] are: 5.997(59)(111), 3.138(83)(311), 3.005(100)(222), 2.602(29)(400), 2.004(23)(511), 1.841(23)(440), 1.589(25)(533), and 1.504(24)(444). The crystal structure refinement (R1 = 0.0132) gave the following data: cubic, Fd3̅m, a = 10.4191(6) Å, V = 1131.07(11) Å3, Z = 8.

Crystal structure of the (Mg,Fe)[UO2(P,As)O4]2 · 10H2O solid solution—A novel mineral variety of saléeite

The crystal structure of a novel variety {[(Mg0.81Fe0.19)(H2O)6](H2O)4}{(UO2)[(P0.67As0.33)O4]}2 of the mineral saléeite is determined using X-ray diffraction (Bruker Smart diffractometer, λMoKα, graphite monochromator, 2θmax = 56.62°, R = 0.0321 for 2317 reflections, T = 100 K). The main crystal data are as follows: a = 6.952(6) Å, b = 19.865(5) Å, c = 6.969(2) Å, β = 90.806(4)°, space group P121/n1, Z = 2, and ρcalcd = 3.34 g/cm3. It is shown that the structure is formed by alternating (along the [010] direction) anionic layers, which are composed of uranium bipyramids and T(P,As) tetrahedra, and cation layers consisting of M(Mg,Fe) octahedra and water molecules, which are joined through a system of asymmetric hydrogen bonds. The hydrogen atoms are located, the scheme of hydrogen bonds is established, and their geometric characteristics are calculated.