Stronadelphite, Sr5(PO4)3F, a new apatite-group mineral

The new apatite-group mineral stronadelphite was found in the Belovitovoye peralkaline pegmatite at the Kirovskii apatite mine, Mt. Kukisvumchorr, Khibiny alkaline complex, Kola peninsula, Russia. Associated minerals are natrolite, microcline, aegirine, pectolite, lamprophyllite, belovite-(Ce), belovite-(La), gaidonnayite, nenadkevichite, komarovite, manganokukisvumite, epididymite, sphalerite, neotocite, etc. Stronadelphite forms hexagonal, prismatic to acicular crystals up to 0.1 0.1 2 mm, combined in sheaf-like clusters up to 1 2 mm embedded in natrolite. The mineral is transparent, colourless with a pale greenish tint. Stronadelphite is brittle, with Mohs hardness 5, no cleavage observed. Dcalc is 3.915 g/cm3. Optically, the new mineral is uniaxial (–), omega 1.630(1), epsilon 1.623(1). Average values for six point microprobe analyses (wt%) are: Na2O 0.10, CaO 2.49, SrO 62.72, BaO 2.40, La2O3 0.34, Ce2O3 0.22, ThO2 0.28, P2O5 29.02, F 1.45, H2O(calc.) 0.54, –O=F2 0.61; total 98.95. The empirical formula based on 13 anions [O12(F,OH)] is: (Sr4.46Ca0.33Ba0.12Na0.02La0.02Ce0.01Th0.01)sum=4.97 P3.01O12[F0.56(OH)0.44]sum=1. The idealized formula is Sr5(PO4)3F. Stronadelphite is hexagonal, space group P63/m; a = 9.845(7), c = 7.383(4) Å, V = 619.7(7) Å3, Z = 2. Its crystal structure has been refined to R = 0.0305 using single-crystal X-ray diffraction data. Stronadelphite is isostructural with fluorapatite. The strongest lines of the powder diffraction pattern [d in Å (I) (hkl)] are: 3.71 (30) (002), 3.21 (40) (120, 210), 2.940 (100) (211, 121, 112), 2.823 (35) (300, 202), 2.009 (50) (222, 312, 132), 1.955 (45) (213, 123), 1.500 (30) (151, 511, 332). The mineral is named after the chemical element strontium and adelphos, Greek for "brother", as the full strontium analogue of fluorapatite, the most widespread member of the apatite supergroup. Both the mineral and its name have been approved by the IMA CNMNC. The type specimen is deposited in Fersman Mineralogical Museum, Moscow, with the registration number 3693/1

Crystal structure of cation-deficient calciohilairite and possible mechanisms of decationization in mixed-framework minerals

The crystal structure of cation-deficient calciohilairite from the Lovozero massif (the Kola Peninsula) was established (Siemens P4 diffractometer, MoK-alpha radiation, 409 independent reflections with |F| > 4sigma(F), anisotropic refinement, R(F) = 0.037). Like other representatives of the hilairite structure type, calciohilairite is described by the space group R32 (a = 10.498(2) Å, c = 7.975(2) Å, Z = 3), whereas its unit-cell parameter c is reduced by a factor of two. Two positions in the cavities of the mixed zirconium–silicon–oxygen framework are occupied by Ca and Na cations in the ratio of 1 : 1 (partly occupied A(1) position) and oxonium cations (H3O)+ and H2O molecules in the ratio of 1 : 2 (A(2) position). Different types of isomorphous replacement accompanying the formation of cation-deficient mixed-framework structures (lovozerite, vinogradovite–lintisite, labuntsovite–nenadkevichite, eudialyte, etc.) are considered. Based on the X-ray diffraction data, the following scheme of isomorphism in the structure of cation-deficient calciohilairite is suggested: 2Na+ + H2O = 0.5Ca2+ + 1.5* + (H3O)+, where * is a vacancy

Nomenclature of the apatite supergroup minerals

The apatite supergroup includes minerals with a generic chemical formula IXM12VIIM23(IVTO4)3X (Z = 2); chemically they can be phosphates, arsenates, vanadates, silicates, and sulphates. The maximum space group symmetry is P63/m, but several members of the supergroup have a lower symmetry due to cation ordering and deviations from the ideal topology, which may result in an increase of the number of the independent sites. The apatite supergroup can be formally divided into five groups, based on crystal-chemical arguments: apatite group, hedyphane group, belovite group, britholite group, and ellestadite group. The abundance of distinct ions which may be hosted at the key-sites [M = Ca2+, Pb2+, Ba2+, Sr2+, Mn2+, Na+, Ce3+, La3+, Y3+, Bi3+; T = P5+, As5+, V5+, Si4+, S6+, B3+; X = F-, (OH)-, Cl-] result in a large number of compositions which may have the status of distinct mineral species. Naming of apatite supergroup minerals in the past has resulted in nomenclature inconsistencies and problems. Therefore, an ad hoc IMA-CNMNC Subcommittee was established with the aim of rationalizing the nomenclature within the apatite supergroup and making some order among existing and potentially new mineral species. In addition to general recommendations for the handling of chemical (EPMA) data and for the allocation of ions within the various sites, the main recommendations of this subcommittee are the following: 1. Nomenclature changes to existing minerals. The use of adjectival prefixes for anions is to be preferred instead of modified Levinson suffixes; accordingly, six minerals should be renamed as follows: apatite-(CaF) to fluorapatite, apatite-(CaOH) to hydroxylapatite, apatite-(CaCl) to chlorapatite, ellestadite-(F) to fluorellestadite, ellestadite-(OH) to hydroxylellestadite, phosphohedyphane-(F) to fluorphosphohedyphane. For the apatite group species these changes return the names that have been used in thousands of scientific paper, treatises and museum catalogues over the last 150 years. The new mineral IMA 2008-009, approved without a name, is here named stronadelphite. Apatite-(SrOH) is renamed fluorstrophite. Deloneite-(Ce) is renamed deloneite. The new mineral IMA 2009-005 is approved with the name fluorbritholite-(Y). 2. Potentially new mineral species. The following end-member compositions are eligible for status as distinct mineral species; the approved name, if any, is given in parentheses: Ca2Pb3(AsO4)3(OH) (hydroxylhedyphane); Ca2Pb3(PO4)3(OH) (hydroxylphosphohedyphane); Ca2Sr3(PO4)3F (new root name); Mn2Ca3(PO4)3Cl (new root name); Pb5(SiO4)1.5(SO4)1.5(OH) (hydroxylmattheddleite). 3. Minerals and mineral names which could be discredited. The mineral ellestadite-(Cl) is not thought to exist and should be discredited; the name melanocerite-(Ce) should be discontinued [= tritomite-(Ce)]. 4. Changes of status from distinct species to polymorphic variants. Fermorite is the monoclinic polymorph of johnbaumite (= johnbaumite-M); clinohydroxylapatite is the monoclinic polymorph of hydroxylapatite (= hydroxylapatite-M); clinomimetite is the monoclinic polymorph of mimetite (= mimetite-M). 5. Recognition of a new polymorphic variant. A new monoclinic polymorph of apatite is recognized (chlorapatite-M). 6. Changes to end-member formulae. The ideal chemical formula of morelandite is Ca2Ba3(AsO4)3Cl instead of Ba5(AsO4)3Cl; the ideal chemical formula of deloneite is (Na0.5REE0.25Ca0.25) (Ca0.75REE0.25) Sr1.5 (CaNa0.25REE0.25) (PO4)3 F0.5(OH)0.5

The crystal structure of calcium catapleiite

Calcium catapleiite, CaZrSi3O9•2H2O, the calcium-dominant analogue of catapleiite, Na2ZrSi3O9•2H2O, firstly described as hexagonal, space group P63/mmc, with a 7.32, c 10.15 Å, is actually orthorhombic, space group Pbnn, a 7.378(1), b 12.779(1), c 10.096(1) Å, V 951.89 Å3 and Z = 4. The crystals display three-fold twinning (“Drilling”) about the c axis, with the three individuals rotated 120° one from the other. The crystal structure of calcium catapleiite from the type locality, the Burpala massif, northern Baikal Region, Siberia, Russia, has been determined by direct methods from single-crystal X-ray-diffraction data and refined to a final R = 0.0528 (wR2 = 0.1604) for 2167 reflections with Fo > 6(Fo). It is characterized by a mixed framework of regular [ZrO6] octahedra and three-membered silicate rings [Si3O9], very similar to the framework of catapleiite. The H2O molecules also are similarly placed in the two minerals. The Ca2+ cations in calcium catapleiite are distributed over two distinct sites, with 0.8 and 0.2 occupancies, which contrasts with the fully disordered distribution of the Na+ cations in catapleiite

Crystal structures of potassium-exchanged forms of catapleite and hilairite

The crystal structures of potassium-exchanged forms of catapleiite and hilairite of the compositions (K0.49Ca0.42Na0.26) ZrSi3O9 · 2[(H2O)0.8(H3O)0.2] and K0.51ZrSi3O9 · [(H2O)0.5K0.27(H3O)0.23], respectively, were studied by X-ray diffraction and IR spectroscopy. Both structures retain the heteropolyhedral frameworks of the parent minerals formed by Zr octahedra and Si tetrahedra. The K cations occupy different positions in these minerals. In K-exchanged catapleiite, K cations are located only in the position occupied by Na in the structure of the parent mineral. In the K-exchanged form of hilairite, K cations are not only involved in the Na position but also partially occupy the H2O position

Larisaite, Na(H3O)(UO2)3(SeO3)2O2.4H2O, a new uranyl selenite mineral from Repete mine, San Juan County, Utah, U.S.A

Larisaite, a new uranyl selenite with the idealized formula Na(H3O)(UO2)3(SeO3)2O2 ·4H2O, has been found in a sedimentary rock from Repete mine near Blanding, San Juan Co., Utah, U.S.A., in association with quartz, haynesite, andersonite, wölsendorfite, uranophane, gypsum, calcite and montmorillonite. The mineral is named in memory of Russian mineralogist and crystallographer Larisa Nikolaevna Belova (1923-1998) who made a significant contribution to the knowledge on the uranium minerals. Larisaite forms coarse lamellar crystals up to 1 mm and radial aggregates up to 2 mm. It is transparent or translucent, yellow, lustre vitreous, streak yellow. Fluorescence under the UV light is green (wavelengths of excitation 250 nm). Larisaite is sectile, with Mohs’ hardness 1, perfect cleavage on (010) and uneven fracture across the cleavage direction. Calculated density is 4.50 g/cm3 from the crystal structure refinement and 4.46 g/cm3 from the empirical formula. Optically biaxial (-), alpha 1.597(2), beta 1.770(5), gamma 1.775(5); 2V = 20°. Dispersion is strong, r alpha (light greenish-yellow). IR spectrum is given. Average values for 3 point microprobe analyses (wt.%, ranges are given in brackets) are: Na2O 2.04 (1.82-2.32), K2O 0.69 (0.62-0.76), CaO 0.23 (0.17-0.30), UO3 72.19 (71.77-72.64), SeO2 18.12 (17.83-18.48); H2O content determined by Penfield method is 7.64; total 100.91 wt.%; contents of Mg, Sr, Ba, Pb, Zn, Mn, Ni, Co, Cu, Fe, Al, Si, S, As, Cl, F are lower than detection limits i. e. < 0.02-0.05%. The empirical formula based on (SeO3)2O2 is: Na0.81K0.18Ca0.05(H3O)0.73(UO2)3.09(SeO3)2O2·4.1H2O. 1-(KP/Kc) = 0.013 (“superior”). The crystal structure has been determined (R=0.067). Larisaite is monoclinic, space group P11m; a = 6.9806(9), b = 7.646(1), c = 17.249(2) Å, gamma = 90.039(4)°, V = 920.64 Å3, Z = 2. The strongest lines in the powder diffraction pattern [d, Å (I,%) (hkl)] are: 8.63 (43) (002), 7.67 (100) (010), 3.85 (40) (-113, 020, 113), 3.107 (77) (211), 2.874 (53) (006, -115). By the U : Se ratio, the values of unit cell parameters and the structure type, larisaite is related to haynesite, guilleminite and piretite. In common with guilleminite, uranium polyhedra and SeO3 triangles form the sheets, however the distribution of interlayer cations and H2O molecules is different. Holotype specimen is deposited in the Geoscientific Collections of Freiberg University of Mining and Technology, Faculty of Geosciences, Geotechnics and Mining, Freiberg, Germany (the inventory number 80251)

Fluorcalciobritholite, (Ca,REE)5[(Si,P)O4]3F, a new mineral: description and crystal chemistry

The new mineral fluorcalciobritholite, ideally Ca3Ce2(SiO4)2(PO4)F, has been found at Mount Kukisvumchorr, Khibiny alkaline complex, Kola Peninsula, Russia, in veinlets which contains aggregates of orthoclase, nepheline, sodalite and biotite in association with grains of fayalite, gadolinite-(Ce), zircon, monazite-(Ce), zirconolite ("polymignite"), fluorapatite, fluorite, molybdenite, löllingite and graphite. Fluorcalciobritholite forms long-prismatic hexagonal crystals up to 0.5 x 10 mm; the main crystal form is the hexagonal prism {10-10}. The mineral is transparent, with a pale pinkish to brown colour and a white streak. The hardness (Mohs) is 5.5, and the observed density is 4.2(1) g/cm3. Optically, it is uniaxial (-) with omega 1.735(5), epsilon 1.730(5). Electron microprobe gave the following empirical formula based on [Si+P+S] = 3 apfu: [Ca2.80(Ce0.93La0.54Nd0.26Y0.18Pr0.08Sm0.03Gd0.03Dy0.02Yb0.02Er0.01)sum=2.12 Th0.04Mn0.03 Sr0.02]sum=4.99 [(Si1.94P1.06)sum=3 O12] [F0.76O0.22Cl0.01]sum=0.99 (Z = 2). The IR spectrum of metamict fluorcalciobritholite from Siberia showed a marked similarity with those of hydroxylbritholite-(Ce) and hydroxylbritholite-(Y). The strongest lines of the X-ray powder pattern [d in Å (I) (hkl)] are: 3.51 (45) 002, 3.15 (70) 102, 2.85 (100) 211, 121, 2.78 (60) 300. The mineral is hexagonal, space group P63/m, with a = 9.580(7), c = 6.985(4) Å, V = 555.2(7) Å3. The crystal structure was refined from single-crystal X-ray diffraction data to RF = 0.029. Fluorcalciobritholite, whose simplified formula is (Ca,REE)5[(Si,P)O4]3F, differs from fluorbritholite in having Ca > sumREE, and differs from fluorapatite in having Si 8 P. Its compositional field falls within the limits Ca2.5REE2.5(SiO4)2.5(PO4)0.5F (boundary with fluorbritholite) and Ca3.5REE1.5(SiO4)1.5(PO4)1.5F (boundary with fluorapatite). Both the mineral and its name have been approved by the IMA Commission on New Minerals and Mineral Names