• Fluorlamprophyllite, Na-3(SrNa)Ti-3(Si2O7)(2)O2F2, a new mineral from Pocos de Caldas alkaline massif, Morro do Serrote, Minas Gerais, Brazil

      Andrade, Marcelo B.; Yang, Hexiong; Downs, Robert T.; Färber, Gunnar; Contreira Filho, Reynaldo R.; Evans, Stanley H.; Loehn, Clayton W.; Schumer, Benjamin N.; Univ Arizona, Dept Geosci (MINERALOGICAL SOC, 2018-02)
      A new mineral species, fluorlamprophyllite (IMA2013-102), ideally Na3(SrNa)Ti-3(Si2O7)(2)O2F2, has been found in the Pocos de Caldas alkaline massif, Morro do Serrote, Minas Gerais, Brazil. Alternatively, the idealized chemical formula could be written as (SrNa)[(Na3Ti)F-2][Ti-2(Si2O7)(2)O-2], 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 similar to 3; cleavage is perfect on {100} and no parting was observed. The calculated density is 3.484 g/cm(3). Optically, fluorlamprophyllite is biaxial (+), with alpha= 1.735(7), beta = 1.749(7) and gamma = 1.775(9) and 2V(meas) = 72(3)degrees. 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)(Sigma 4.90)(Ti2.63Fe0.24Al0.04)(Sigma 2.91)Si3.89O16[F-1.15(OH)(0.85)](Sigma 2.00). 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) A, beta = 96.794(2)degrees and V = 727.5(1) A(3). The structure is a layered silicate inasmuch as the O atoms are arranged in well-defined, though not necessarily close-packed layers.
    • Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

      Andrade, M. B.; Yang, H.; Atencio, D.; Downs, R. T.; Chukanov, N. V.; Lemée-Cailleau, M. H.; Persiano, A. I. C.; Goeta, A. E.; Ellena, J.; Univ Arizona, Dept Geosci (MINERALOGICAL SOC, 2017-05-01)
      Hydroxycalciomicrolite, 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 to 1.5 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 56. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm(3). Hydroxycalciomicrolite is isotropic, n(calc). = 2.010. The infrared and Raman spectra exhibit bands due to OH stretching vibrations. The chemical composition determined from electron microprobe analysis (n = 13) is (wt.%): Na2O 0.36(8), CaO 15.64(13), SnO2 0.26(3), Nb2O5 2.82(30), Ta2O5 78.39(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)(Sigma 1.55)(Ta1.88Nb0.11Sn0.01)S2.00O6.00[(OH)(0.76)F0.20O0.04]. Hydroxycalciomicrolite is cubic, with unit-cell parameters a = 10.4205(1) angstrom, V = 1131.53(2) angstrom(3) and Z = 8. It represents a pyrochlore supergroup, microlite-group mineral exhibiting P4(3)32 symmetry, instead of Fd (3) over barm. The reduction in symmetry is due to long-range ordering of Ca and vacancies on the A sites. 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 with P4(3)32 or lower-symmetry space group can be discovered and characterized.
    • Lipuite, a new manganese phyllosilicate mineral from the N'Chwaning III mine, Kalahari Manganese Fields, South Africa

      Gu, Xiangping; Yang, Hexiong; Xie, Xiande; van Nieuwenhuizen, Jaco J.; Downs, Robert T.; Evans, Stanley H.; Univ Arizona, Dept Geosci (MINERALOGICAL SOC, 2019-02-26)
      A new phyllosilicate mineral, lipuite (IMA2014-085), has been discovered from the N'Chwaning III mine, Kalahari Manganese Fields, Northern Cape Province, Republic of South Africa. It occurs as platy, tabular, or granular crystals and veined agglomerate in association with Mn-bearing sugilite, taniajacoite, pectolite, richterite, norrishite and namansilite. Lipuite is dark red-brown with vitreous lustre, red streak, an estimated Mohs hardness of 5 and the measured density is 2.83(3) g/cm(3). It is biaxial (+) and characterised by bright red to dark red colour in thin section with measured refractive indices in white light: alpha= 1.635(1), beta= 1.653(1), gamma = 1.670(1) and 2V = 86(2)degrees. The Raman spectra of lipuite are composed of over 21 bands at 109, 146, 162, 183, 206, 244, 288, 342, 362, 455, 496, 520, 552, 613, 669, 886, 930, 971, 1097, 3487 and 3540 cm(-1). The empirical formula from microprobe analyses is (based on total number of cations = 27.5 and structural refinement): K1.12Na8.16(Mn4.77Fe0.07)(Sigma 4)Mg-.(84)0(.44)[Si11.97O30(OH)(4)](PO4)(0.94)O-2(OH)(2 center dot)4H(2)O. The idealised formula is: KNa(8)Mn5(3+)Mg(0.5)Si(12)O(30)(OH)(4)] (PO4)O-2(OH)(2)center dot 4H(2)O. Lipuite is orthorhombic, space group Pnnm, a = 9.080(3), b = 12.222(3), c = 17.093(5) angstrom, V = 1897.0(9) angstrom(3) and Z = 2. The strongest powder X-ray diffraction peaks [d, angstrom (I) (hkl)] are: 9.965(40)(011), 2.938(33)(310), 2.895(100)(311), 2.777(38)(224), 2.713(53)(320), 2.483(32)(126), 2.086(35)(046) and 1.534(40)(446). The crystal structure of lipuite is characterised by sheets of SiO4 tetrahedra that are linked together along [010] by K+, Na+, Mn3+, Mg2+ and P5+ cations, as well as hydrogen bonds. These tetrahedral sheets consist of 14-membered rings of SiO4 tetrahedra that zigzag along [100]. The two independent Mn3+ cations are both octahedrally coordinated. They form five-membered, edge-shared octahedral clusters between the SiO4 tetrahedral sheets. Lipuite represents a rather unique structure type and its silicate tetrahedral sheets can be considered a derivative of the silicate sheets in mica.
    • Natropalermoite, Na2SrAl4(PO4)(4)(OH)(4), a new mineral isostructural with palermoite, from the Palermo No. 1 mine, Groton, New Hampshire, USA

      Schumer, Benjamin N.; Yang, Hexiong; Downs, Robert T.; Univ Arizona, Dept Geosci (MINERALOGICAL SOC, 2017-08-01)
      Natropalermoite, ideally Na2SrAl4(PO4)(4)(OH)(4), the Na-analogue of palermoite, is a new mineral from the Palermo No. 1 mine, Groton, New Hampshire, USA. Associated minerals are palermoite, eosphorite and quartz. Natropalermoite crystals are prismatic with striations parallel to the direction of elongation (the a axis) up to 200 mu m x 50 mu m x 45 mu m in size. The mineral is colourless, transparent with a white streak and vitreous lustre and is visually indistinguishable from palermoite. It is brittle with subconchoidal fracture and has a Mohs hardness of 5.5. Cleavage is perfect on {001}, fair on {100} and no parting was observed. The calculated density is 3.502 g cm(-3). Natropalermoite is biaxial (-), alpha = 1.624(1), ss = 1.641(1), gamma = 1.643(1) (589 nm), 2V(meas) = 43(4)degrees, 2V(calc) = 38 degrees. An electronmicroprobe analysis yielded an empirical formula (based on 20 O apfu) of (Na1.69Li0.31)(Sigma 2.00) (Sr0.95Mg0.04C a(0.02)Ba(0.01))(Sigma 1.02) (Al3.82Mn0.03Fe0.03)(Sigma 3.88) (P1.01O4)(4)(OH)(4). Natropalermoite is orthorhombic, space group Imcb, a = 11.4849(6), b = 16.2490(7), c = 7.2927(4) angstrom, V = 1360.95(17) A(3), Z = 4. Natropalermoite is isotypic with palermoite, but substitution of the larger Na for Li results in substantial increase of the b cell parameter. Four of the seven Na-O distances are longer than their equivalents in palermoite, resulting in a more regular 7-fold coordination polyhedron about Na. The eight strongest peaks in the calculated X-ray powder diffraction are [d(calc) (angstrom), I-rel%, (hkl)]: [3.128, 100, (321)], [4.907, 68, (121)], [3.327, 48, (022)], [4.689, 45, (220)], [3.078, 45, (202)], [2.453, 38, (242)], [2.636, 35, (411)], [2.174, 35, (422)].
    • New data on hemihedrite from Arizona

      Lafuente, B.; Downs, R. T.; Origlieri, M. J.; Domanik, K. J.; Gibbs, R. B.; Rumsey, M. S.; Univ Arizona, Dept Geosci; Univ Arizona, Lunar & Planetary Lab (MINERALOGICAL SOC, 2017-08-01)
      Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USA was first described and assigned the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)F-2, based upon a variety of chemical and crystal-structure analyses. The primary methods used to determine the fluorine content for hemihedrite were colorimetry, which resulted in values of F that were too high and inconsistent with the structural data, and infrared (IR) spectroscopic analysis that failed to detect OH or H2O. Our reinvestigation using electron microprobe analysis of the type material, and additional samples from the type locality, the Rat Tail claim, Arizona, and Nevada, reveals the absence of fluorine, while the presence of OH is confirmed by Raman spectroscopy. These findings suggest that the colorimetric determination of fluorine in the original description of hemihedrite probably misidentified F due to the interferences from PO4 and SO4, both found in our chemical analyses. As a consequence of these results, the study presented here proposes a redefinition of the chemical composition of hemihedrite to the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)(OH)(2). Hemihedrite is isotypic with iranite with substitution of Zn for Cu, and raygrantite with substitution of Cr for S. Structural data from a sample from the Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space group P (1) over bar, a = 9.4891(7), b = 11.4242(8), c = 10.8155(7) angstrom, alpha = 120.368(2)degrees, ss = 92.017(3)degrees, gamma = 55.857(2)degrees, V = 784.88(9) angstrom(3), Z = 1, consistent with previous investigations. The structure was refined from single-crystal X-ray diffraction data to R-1 = 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)(OH)(2) was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb-10.05(Zn0.91Mg0.02)(Sigma) (= 0.93) (Cr5.98S0.01P0.01)(Sigma = 6.00) Si1.97O34 H-2.16 based on 34 O atoms and six (Cr + S + P) per unit cell.
    • Parisite-(La), ideally CaLa2(CO3)(3)F-2, a new mineral from Novo Horizonte, Bahia, Brazil

      Menezes Filho, Luiz A. D.; Chaves, Mario L. S. C.; Chukanov, Nikita V.; Atencio, Daniel; Scholz, Ricardo; Pekov, Igor; da Costa, Geraldo Magela; Morrison, Shaunna M.; Andrade, Marcelo B.; Freitas, Erico T. F.; et al. (MINERALOGICAL SOC, 2018-02)
      Parisite-(La) (IMA2016-031), ideally CaLa2(CO3)(3)F2, occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remedios Group, at the Mula mine, Tapera village, Novo Horizonte county, Bahia, Brazil, associated with hematite, rutile, almeidaite, fluocerite-(Ce), brockite, monazite-(La), rhabdophane-(La) and bastnasite-(La). Parisite-(La) occurs as residual nuclei (up to 5 mm) in steep doubly-terminated pseudo-hexagonal pyramidal crystals (up to 8.2 cm). Parisite-(La) is transparent, yellow-green to white, with a white streak and displays a vitreous (when yellow-green) to dull (when white) lustre. Cleavage is distinct on pseudo-{001}; fracture is laminated, conchoidal, or uneven. The Mohs hardness is 4 to 5, and it is brittle. Calculated density is 4.273 g cm(-3). Parisite-(La) is pseudo-uniaxial (+), omega = 1.670(2) and epsilon = 1.782(5) (589 nm). The empirical formula normalized on the basis of 11 (O + F) atoms per formula unit (apfu) is Ca0.98(La0.83Nd0.51Ce0.37Pr0.16Sm0.04Y0.03)(Sigma 1.94)C3.03O8.91F2.09. The IR spectrum confirms the absence of OH groups. Single-crystal X-ray studies gave the following results: monoclinic (pseudo-trigonal), space group: C2, Cm, or C2/m, a = 12.356(1) angstrom, b = 7.1368(7) angstrom, c = 28.299(3) angstrom, beta = 98.342(4)degrees, V = 2469.1(4) angstrom(3) and Z = 12. Parisite-(La) is the La-dominant analogue of parisite-(Ce).