New Data on the Isomorphism in Eudialyte-Group Minerals. 2. Crystal-Chemical Mechanisms of Blocky Isomorphism at the Key Sites

The review considers various complex mechanisms of isomorphism in the eudialyte-group minerals, involving both key positions of the heteropolyhedral framework and extra-framework components. In most cases, so-called blocky isomorphism is realized when one group of atoms and ions is replaced by another one, which is accompanied by a change in the valence state and/or coordination numbers of cations. The uniqueness of these minerals lies in the fact that they exhibit ability to blocky isomorphism at several sites of high-force-strength cations belonging to the framework and at numerous sites of extra-framework cations and anions

New Data on the Isomorphism in Eudialyte-Group Minerals. 1. Crystal Chemistry of Eudialyte-Group Members with Na Incorporated into the Framework as a Marker of Hyperagpaitic Conditions

A review of the crystal chemistry of Fe-deficient eudialyte-group minerals is given. Specific features of cation distribution over key sites in the crystal structure, including partial substitution of Fe2+ with Na, Mn and Zr at the M2 site are discussed. It is concluded that Na-dominant (at the M2 site) eudialyte-group members (M2Na-EGMs) are markers of specific kinds of specific peralkaline (hyperagpaitic) igneous rocks and pegmatites. New data are obtained on the chemical composition, IR spectra and crystal chemistry for two samples of M2Na-EGMs with disordered M1 cations, which are a potentially new mineral species with the simplified formula (Na,H2O)15Ca6Zr3[Na2(Fe,Zr)][Si26O72](OH)2Cl·nH2O

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

Footemineite, ideally Ca2Mn2+square Mn22+Be4(PO4)(6)(OH)(4)-6H(2)O, 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 I 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 {0 (1) over bar1}) and {100}. Density (calc.) is 2.873 g/cm(3). Footemineite is biaxial (-), n(alpha) = 1.620(2), n(beta) = 1.627(2), n(gamma) = 1.634(2) (white light). 2V(obs) = 80 degrees, 2V(calc) = 89.6 degrees. Orientation: X boolean AND b similar to 12 degrees, Y boolean AND c similar to 15 degrees, Z boolean AND a similar to 15 degrees. Elongation direction is c, dispersion: r > v or r < v, weak. Pleochroism: beta (brownish yellow) > alpha = gamma (yellow). Mossbauer and IR spectra are given. The chemical composition is (EDS mode electron microprobe, Li and Be by ICP-OES, Fe3+:Fe2+ y Mossbauer, 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)Sigma(1.94)(Mn-0.90(2+)square(0.10))Sigma(1.00)(square 0.78Li0.17Mg0.05) Sigma(1.00)(Mn3.252+Fe0.432+ Fe0.093+Al0.03)Sigma(3.80) Be-4.30(P5.81Si0.08O24)[(OH)3.64(H2O)0.36]Sigma(4.00)center dot 6.00H(2)O . The strongest reflection peaks of the powder diffraction pattern [d, angstrom (1, %) (hkl)] are 9.575 (53) (010), 5.998 (100) (0 (1) over bar1), 4.848 (26) (021), 3.192 (44) (210), 3.003 (14) (0 (2) over bar2), 2.803 (38) ((1) over bar 03), 2.650 (29) ((2) over bar 02), 2.424 (14) (231). Single-crystal unit-cell parameters are a = 6.788(2), b = 9.972(3), c = 10.014(2) A, (x = 73.84(2), beta = 85.34(2), gamma = 87.44(2)degrees,V = 648.74 angstrom(3), Z = 1. The space group is P (1) over bar. Crystal structure was refined to R = 0.0347 with 1273 independent reflections (F > 2(5). 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

A new mineral species rossovskyite, (Fe3+,Ta)(Nb,Ti)O4: crystal chemistry and physical properties

A new mineral rossovskyite named after L.N. Rossovsky was discovered in granite pegmatites of the Bulgut occurrence, Altai Mts., Western Mongolia. Associated minerals are microcline, muscovite, quartz, albite, garnet of the almandine–spessartine series, beryl, apatite, triplite, zircon, pyrite, yttrobetafite-(Y) and schorl. Rossovskyite forms flattened anhedral grains up to 6 × 6 × 2 cm. The color of the mineral is black, and the streak is black as well. The luster is semi-metallic, dull. Mohs hardness is 6. No cleavage or parting is observed. Rossovskyite is brittle, with uneven fracture. The density measured by the hydrostatic weighing method is 6.06 g/cm2, and the density calculated from the empirical formula is 6.302 g/cm3. Rossovskyite is biaxial, and the color in reflection is gray to dark gray. The IR spectrum contains strong band at 567 cm−1 (with shoulders at 500 and 600 cm−1) corresponding to cation–oxygen stretching vibrations and weak bands at 1093 and 1185 cm−1 assigned as overtones. The reflection spectrum in visible range is obtained. According to the Mössbauer spectrum, the ratio Fe2+:Fe3+ is 35.6:64.4. The chemical composition is as follows (electron microprobe, Fe apportioned between FeO and Fe2O3 based on Mössbauer data, wt%): MnO 1.68, FeO 5.92, Fe2O3 14.66, TiO2 7.69, Nb2O5 26.59, Ta2O5 37.51, WO3 5.61, total 99.66. The empirical formula calculated on four O atoms is: Mn2+0.06Mn0.062+ Fe2+0.21Fe0.212+ Fe3+0.47Fe0.473+Ti0.25Nb0.51Ta0.43W0.06O4. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is monoclinic, space group P2/c, a = 4.668(1), b = 5.659(1), c = 5.061(1) Å, β = 90.21(1)º; V = 133.70(4) Å3, Z = 2. Topologically, the structure of rossovskyite is analogous to that of wolframite-group minerals. The crystal-chemical formula of rossovskyite is [(Fe3+, Fe2+, Mn)0.57Ta0.32Nb0.11][Nb0.40Ti0.25Fe0.18Ta0.11W0.06]O4. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are as follows: 3.604 (49) (110), 2.938 (100) (−1−11), 2.534 (23) (002), 2.476 (29) (021), 2.337 (27) (200), 1.718 (26) (−202), 1.698 (31) (−2−21), 1.440 (21) (−311). The type specimen of rossovskyite is deposited in the Mineralogical Museum of the Tomsk State University, Tomsk, 634050 Russia, with the inventory number 20927

Eleonorite, Fe3+6 (PO4)4O(OH)4?6H2O : validation as a mineral species and new data.

Eleonorite, ideally Fe3? 6 (PO4)4O(OH)4?6H2O, the analogue of beraunite Fe2+Fe3? 5 (PO4)4(OH)5?6H2O with Fe2+ completely substituted by Fe3+, has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification as a mineral species (IMA 2015-003). The mineral was first described on material from the Eleonore Iron mine, D?nsberg, near Giessen, Hesse, Germany, but during this study further samples were required and a neotype locality is the Rotl?ufchen mine, Waldgirmes, Wetzlar, Hesse, Germany, where eleonorite is associated with goethite, rockbridgeite, dufr?nite, kidwellite, variscite, matulaite, planerite, cacoxenite, strengite and wavellite. Usually eleonorite occurs as red-brown prismatic crystals up to 0.2 mm ? 0.5 mm ? 3.5 mm in size and in random or radial aggregates up to 5 mm across encrusting cavities in massive ?limonite?. The mineral is brittle. Its Mohs hardness is 3. Dmeas = 2.92(1), Dcalc = 2.931 g cm?3 . The IR spectrum is given. Eleonorite is optically biaxial (+), ? = 1.765(4), ? = 1.780(5), ? = 1.812(6), 2Vmeas = 75(10)?, 2Vcalc = 70?. The chemical composition (electron microprobe data, H2O analysed by chromatography of products of ignition at 1200?C, wt.%) is: Al2O3 1.03, Mn2O3 0.82, Fe2O3 51.34, P2O5 31.06, H2O 16.4, total 99.58. All iron was determined as being trivalent from a M?ssbauer analysis. The empirical formula (based on 27 O apfu) is (Fe3? 5:76Al0.18Mn3? 0:09)?6.03(PO4)3.92O(OH)4.34?5.98H2O. The crystal structure (R = 0.0633) is similar to that of beraunite and is based on a heteropolyhedral framework formed by M(1?4)?6-octahedra (where M = Fe3+; ?=O2? , OH? or H2O) and isolated PO4 tetrahedra, with a wide channel occupied by H2O molecules. Eleonorite is monoclinic, space group C2/c, a = 20.679(10), b = 5.148(2), c = 19.223(9) ?, ? = 93.574(9)?, V = 2042.5(16) ?3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d,? (I,%) (hkl)] are 10.41 (100) (200), 9.67 (38) (002), 7.30 (29) (202), 4.816 (31) (111, 004), 3.432 (18) (600, 114, 404, 313), 3.197 (18) (510, 511, 006, 314, 602), 3.071 (34) (314, 115)

Magnesiovoltaite, K2Mg5Fe3+3Al(SO4)12?18H2O, a new mineral from the Alcaparrosa mine, Antofagasta region, Chile.

Magnesiovoltaite, a new voltaite-group mineral, was discovered in the Alcaparrosa mine, Cerro Alcaparrosa, El Loa province, Antofagasta region, Chile, in two associations, one of which includes coquimbite, tamarugite, alum-(Na), rhomboclase, yavapaiite, voltaite and opal, and the other one is botryogen, opal, tamarugite, alum-(K), pickeringite, magnesiocopiapite, and jarosite. Magnesiovoltaite forms yellow, brownish-yellow or pale yellowish-greenish isometric crystals up to 2 mm across. The main crystal forms are {111} and {100}; the subordinate forms are {110} and {211}. The new mineral is brittle, with subconchoidal fracture; cleavage is not observed. Mohs? hardness is 2?. Dmeas = 2.51(2) g/cm3, Dcalc = 2.506 g/cm3. Magnesiovoltaite is optically anomalously anisotropic, uniaxial with ? = 1.584(2) and ? = 1.588(2), or biaxial (?) with ? = 1.584(2), ? = 1.587(2), and ? = 1.588 (2). Possible causes of the optical anomalies are discussed. The infrared spectrum is given. The chemical composition is (EDS-mode electron microprobe, all iron is considered as Fe3+ in accordance with M?ssbauer data, H2O by gas chromatography of ignition products, wt. %): Na2O 0.13, K2O 4.64, MgO 9.13, MnO 1.73, ZnO 0.84, Al2O3 2.47, Fe2O3 13.36, SO3 50.83, H2O 17.6, total 100.73. The empirical formula based on 66 O atoms per formula unit (apfu) is (K1.85Na0.08)(Mg4.25Mn0.46Zn0.14)Fe3+ 3.14Al0.91(SO4) 11.91(H2O)18.325O0.035. The simplified formula is K2Mg5Fe3+ 3Al(SO4)12?18H2O. The crystal structure has been refined to R = 3.2% using 1147 unique reflections with I > 2?(I). Magnesiovoltaite is cubic, Fd?3c, a = 27.161(1) ?, V = 20038(2) ?3, and Z = 16. Magnesiovoltaite is isostructural with other cubic voltaite-group minerals. The strongest lines of the powder X-ray diffraction pattern [d, ? (I, %) (hkl)] are: 9.56 (29) (022), 6.77 (37) (004), 5.53 (61) (224), 3.532 (68) (137), 3.392 (100) (008), 3.034 (45) (048), 2.845 (30) (139). The type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia