Mark A. Cooper

Symesite, Pb10 (SO4) O7 Cl4 (H2O), a new PbO-related sheet mineral: Description and crystal structure

Abstract Symesite, Pb10(SO4)O7Cl4(H2O), is a Pb sheet mineral found in the oxidized zone of a Carboniferous Mn-Pb-Cu deposit at Merehead Quarry, Somerset. It occurs as pink crystal blebs up to 2 mm long and as pink crystalline aggregates up to 1 cm in diameter, and is associated with cerussite, hydrocerussite, paralaurionite, blixite, chloroxiphite, pyrolusite, coronadite, hematite, parkinsonite, and mereheadite. Crystals of symesite are blocky, translucent pink with a vitreous luster and a white streak. Mohs hardness is 4, Dmeas = 7.3(2) g/cm3 and there is a perfect cleavage parallel to {001}; the refractive indices exceed 2. Electron-microprobe analysis gave the following composition (wt%): PbO 90.66, SO3 3.15, Cl 5.83 (O = Cl 1.32), sum 98.32, giving the anhydrous formula Pb10.31S1.00O11.22Cl4.18; solution of the crystal structure gave the ideal formula Pb10(SO4)O7Cl4(H2O). The six strongest peaks in the X-ray powder-diffraction pattern [d in Å, (I), (hkl)] are: 2.911 (10)(414, 32̅3), 3.286 (9)(004), 2.955 (9)(412̅), 2.793 (8)(711̅, 131), 6.573 (4)(002), 3.768 (4)(412, 32̅1). The structure of symesite was solved by direct methods and refined to an R index of 4.0%. Symesite is triclinic, space group B1̅, a = 19.727(2), b = 8.796(1), c = 13.631(2) Å, α = 82.21(1), β = 78.08(1), γ = 100.04(1)°, V = 2242.4(5) Å3, Z = 4. The structural unit of symesite is a [Pb10(SO4)O7]4+ single sheet; adjacent sheets are linked by layers of Cl. One-eleventh of the Pb atoms are replaced by S, with the addition of an apical oxygen to form an SO4 tetrahedron and a compensating O vacancy within the PbO sheet. The distribution of Pb and SO4 groups is highly ordered and defines a 22 cation-site superstructure motif within the PbO sheet. Eight of eleven interlayer anion sites are occupied by Cl, two are occupied by O of H2O groups, and one site is vacant. Incident bond-valence sums at O atoms indicate that hydrogen bonds occur between the H2O group and the apical oxygen of the SO4 group, providing additional linkage between adjacent PbO sheets. The structure of symesite is closely related to those of tetragonal PbO and the family of PbO-related sheet minerals that includes nadorite, thorikosite, mereheadite, parkinsonite, and kombatite. There are ten non-equivalent Pb sites with coordination numbers of five, seven, or eight; these polyhedra are variants of the Pb[O4Cl4] square-antiprism that is characteristic of these minerals.

PEZZOTTAITE FROM AMBATOVITA, MADAGASCAR: A NEW GEM MINERAL

Pezzottaite, ideally Cs(Be_2Li)Al_2Si_6O_(18), is a new gem mineral that is the Cs,Li–rich member of the beryl group. It was discovered in November 2002 in a granitic pegmatite near Ambatovita in central Madagascar. Only a few dozen kilograms of gem rough were mined, and the deposit appears nearly exhausted. The limited number of transparent faceted stones and cat’s-eye cabochons that have been cut usually show a deep purplish pink color. Pezzottaite is distinguished from beryl by its higher refractive indices (typically n_o=1.615–1.619 and n_e=1.607–1.610) and specific gravity values (typically 3.09–3.11). In addition, the new mineral’s infrared and Raman spectra, as well as its X-ray diffraction pattern, are distinctive, while the visible spectrum recorded with the spectrophotometer is similar to that of morganite. The color is probably caused by radiation-induced color centers involving Mn^(3+).

Verbeekite, monoclinic PdSe2, a new mineral from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo

Abstract Verbeekite, ideally PdSe2, monoclinic with space-group choices C2/m, C2 or Cm; a = 6.659(7), b = 4.124(5), c = 4.438(6) Å, β = 92.76(3)8, V = 121.7(4) Å3; a:b:c = 1.6147:1:1.0761, Z = 2, is a new, very rare, primary mineral, intimately associated with secondary oosterboschite {(Pd,Cu)7Se5}, from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo. Additional associated minerals are Cu- and Pd-bearing trogtalite {(Co,Cu,Pd)Se2}, Se-bearing digenite and Se-bearing covellite. The strongest five lines of the X-ray powder-diffraction pattern {d in Å (I) (hkl)} are: 4.423(30)(001), 3.496 (30)(110), 2.718(100)(111), 1.955(50)(310) and 1.896(50)(1̄12). The mineral has also been identified, as a single anhedral 25 μm-sized grain, from Hope’s Nose, Torquay, Devon, England where it is associated with native gold, chrisstanleyite Ag2Pd3Se4, oosterboschite(?), unnamed Pd2HgSe3 and cerussite. At Musonoi, altered verbeekite grains do not exceed 200 μm in size and are anhedral, black, with a black streak and a metallic lustre. The mineral is opaque, brittle, has an uneven fracture, and lacks discernible cleavage. The VHN5 ranges 490-610, mean 550 kp/mm2 (2 indentations), roughly approximating a Mohs’ hardness of 5Ý. Dcalc. = 7.211 g/cm3 for the ideal formula. Electron-microprobe analyses (mean of 4 spot analyses) yielded Pd 39.6, Cu 0.5, Se 58.8, total 98.9 wt.%. The empirical formula is (Pd0.99Cu0.02)∑1.01Se1.99, based on Pd+Cu+Se = 3. In plane-polarized reflected light, the mineral is a nondescript grey and is neither pleochroic nor perceptibly bireflectant. Anisotropy is moderate with rotation tints in varying shades of brown. Reflectance spectra and colour values are tabulated. The name honours Dr Théodore Verbeek (1927-1991) who was the first geoscientist to study the Musonoi palladium mineralization in the Democratic Republic of Congo (1955-1967) and who co-discovered this new mineral phase.

A new anhydrous amphibole from the Eifel region, Germany: Description and crystal structure of obertiite, NaNa2(Mg3Fe3+Ti4+)Si8O22O2

Abstract Obertiite is a new amphibole species from Bellerberg, Laccher See district, Eifel, Germany. It occurs with tridymite, fluororichterite, hematite, rutile, aegirine-augite, kinoshitalite, and fluor-apatite in vugs in volcanic rocks, and crystallized from late-stage hydrothermal fluids associated with recent volcanism. Obertiite occurs as pale-pink elongated blades and divergent aggregates. It is brittle, H = 5, Dcalc = 3.16 g/cm3, has a colorless streak, vitreous luster, and does not fluoresce; it has perfect cleavage on {110} and conchoidal fracture. In plane-polarized light, obertiite is slightly pleochroic in shades of pink to red-orange; X ^ a = 2° (in β obtuse), Z = b, Y ^ c = 12° (in b obtuse) with absorption X ~ Y ~ Z. It is biaxial negative, α = 1.643(1), β =1.657(1), γ = 1.670(3), 2Vx = 81(1)°, no dispersion visible. Obertiite is monoclinic, space group C2/m, a = 9.776(2), b = 17.919(3), c = 5.292(1) Å, b = 104.05(2)°, V = 899.3(3) Å3, Z = 2. The strongest ten X-ray diffraction lines in the powder pattern are [d(I,hkl)]: 8.414(10,110), 2.705(7,331,151), 3.390(6,131), 4.467(5,040), 3.117(5,310), 2.531(5,202), 3.255(3,240), 2.577(3,061), 2.163(3,171,261), 4.013(2,111). Analysis by a combination of electron microprobe, SIMS, and crystal-structure refinement gives SiO2 54.53, Al2O3 0.15, TiO2 7.75, Fe2O3 2.61, Mn2O3 3.27, FeO 3.36, ZnO 0.08, MgO 14.13, Li2O 0.05, CaO 0.52, Na2O 9.51, K2O 0.98, F 0.55, H2O 0.20, O ≡ F -0.23, Ni, Cr, V, Cl not detected, sum 97.46 wt%. The formula unit, calculated on the basis of 24(O,OH,F) is (K0.18Na0.84)(Na1.86Ca0.08Fe2+0.06) (Mg3.09Zn0.01Li0.03Fe3+0.29Mn3+0.37Fe2+0.41Ti4+0.86Al0.03)Si8.00O22[(OH)0.20F0.26O1.54], and is close to the ideal endmember composition Na Na2 (Mg3Fe3+Ti4+) Si8 O22 O2. The crystal structure of obertiite was refined to an R index of 2.6% using MoKa X-ray intensity data. The M1 site is split into two subsites along the b axis, M1 and M1A; the M1 site is occupied by Mg, and M1A is occupied predominantly by Ti4+ and Mn3+; M2 is occupied by Mg, Fe2+, and Fe3+, and M3 is occupied by Mg. Local bond-valence considerations suggest that O2- at O3 is linked to Ti4+Mg or Mn3+Mn3+ at the adjacent M1 and/or M1A sites, and that OH or F at O3 is linked to MgMg at the adjacent M1 sites.

Prismatine: Revalidation for Boron-Rich Compositions in the Kornerupine Group

Abstract Kornerapine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in komerupine ranges from 0 to 1. Koraerapine and prismatine, from their respective type localities of Fiskensesset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer’s name prismatine for komerupines with B > 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name komerupine sensu stricto to komerupines with B < 0.5 p.f.u. Komerupine sensu Iato is an appropriate group name for komerupine of unknown boron content. Komerupine sensu stricto and prismatine from the type localities differ also in Fe2+/Mg ratio, Si - (Mg + Fe2+ + Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but komerupine sensu stricto is associated with anorthite and hornblende or gedrite, whereas prismatine is found with oligoclase (An9-13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of komerupine sensu stricto.

Description and crystal structure of bobkingite, Cu52+Cl2(OH)8(H2O)2, a new mineral from New Cliffe Hill Quarry, Stanton-under-Bardon, Leicestershire, UK

Abstract Bobkingite, ideally Cu2+5 Cl2(OH)8(H2O)2, is a new mineral from the New Cliffe Hill Quarry, Stantonunder- Bardon, Leicestershire, England. It occurs as very thin (≤5 mm) transparent plates up to 0.2 mm across, perched on a compact fibrous crust of malachite and crystalline azurite attached to massive cuprite. Crystals are tabular on {001} with dominant {001} and minor {100} and {110}. Bobkingite is a soft pale blue colour with a pale-blue streak, vitreous lustre and no observable fluorescence under ultraviolet light. It has perfect {001} and fair {100} cleavages, no observable parting, conchoidal fracture, and is brittle. Its Mohs’ hardness is 3 and the calculated density is 3.254 g/cm3. Bobkingite is biaxial negative with α= 1.724(2), β= 1.745(2), γ= 1.750(2), 2Vγmeas = 33(6)8, 2Vcalc = 52°, pleochroism distinct, X = very pale blue, Z = pale greenish blue, X^a = 22° (in β obtuse), Y = c, Z = b. Bobkingite is monoclinic, space group C2/m, unit-cell parameters (refined from powder data): α = 10.301(8), β= 6.758(3), γ = 8.835(7) Å, b = 111.53(6)8, V = 572.1(7) Å3, Z = 2. The seven strongest lines in the X-ray powder-diffraction pattern are [d (Å ), I, (hkl)]: 8.199, 100, (001); 5.502, 100, (110); 5.029, 40, (2̅01); 2.883, 80, (310); 2.693, 40, (1̅13); 2.263, 40, (113), (4̅03); 2.188, 50, (2̅23). Chemical analysis by electron microprobe and crystal-structure solution and refinement gave CuO 70.46, Cl 12.71, H2O 19.19, O:Cl 2.87, sum 99.49 wt.%, where the amount of H2O was determined by crystal-structure analysis. The resulting empirical formula on the basis of 12 anions (including 8 (OH) and 2H2O) is Cu4.99Cl2.02O10H12. The crystal structure was solved by direct methods and refined to an R index of 2.6% for 638 observed reflections measured with X-rays on a single crystal. Three distinct (CuФ6) (Ф= unspecified anion) octahedra share edges to form a framework that is related to the structures of paratacamite and the Cu2(OH)3Cl polymorphs, atacamite and clinoatacamite. The mineral is named for Robert King, formerly of the Department of Geology, Leicester University, prominent mineral collector and founding member of the Russell Society. The mineral and its name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.

The crystal chemistry of sogdianite, a milarite-group mineral

Coarse crystals of niobian rutile occur in the hydrothermally altered core-margin zone of the McGuire granitic pegmatite, Park County, Colorado, associated with potassium feldspar, quartz, biotite, ilmenite, and monazite-(Ce). Primary homogeneous niobian rutile, with Fe ≅ Fe and a small excess of (Fe,Mn) over the amount required to compensate the incorporation of (Nb,Ta,W), underwent three stages of exsolution. Primary homogeneous niobian rutile exsolved a fine trellis-like pattern of minor lamellar Nb-bearing pseudorutile I. Most of this phase was broken down to pseudomorphs consisting of microgranular Nb-rich pseudorutile II imbedded in niobian-ferrian “ferropseudobrookite.” Continued exsolution in niobian rutile and reconstitution of the early exsolution products generated (Fe,Nb)-depleted, microgranular niobian rutile, titanian ferrocolumbite, and minor ilmenite. These three phases did not attain chemical equilibrium but may represent a stable phase assemblage. All these processes seem to have maintained charge balance, suggesting a closed system. Subsequent to the three stages of exsolution, extensive oxidation converted the mineral assemblages to anatase + hematite + titanian-tungstenian ixiolite; primary ilmenite was oxidized into an anatase + hematite intergrowth. In both cases, the hematite component was almost completely leached out, leaving highly porous aggregates of the other phases. The exsolution products in niobian rutile are controlled by the (Fe+Mn+Sc)/(Nb+Ta+W) ratio of the primary phase and by its (Fe+Sc)/ (Fe+Mn) ratio. Dominance of divalent A-cations facilitates exsolution of titanian ferroto manganocolumbite or titanian ixiolite, whereas dominant trivalent cations lead to exsolution of titanian (Fe,Sc)NbO4 phases. Excess (Fe,Mn) over the columbite-type FeNb2 stoichiometry causes exsolution of (Fe,Mn)-rich Nb,Ta-oxide minerals or complementary (Fe,Mn,Ti) phases.

The crystal structure of brunogeierite, Fe2GeO4 spinel

Abstract Brunogeierite, Fe2GeO4, a = 8.4127(7) Å, V = 595.4(1) Å3, is a rare germanate spinel from Tsumeb, Namibia. Its structure has been refined to an R index of 2.2%. The oxygen parameter, u, is 0.2466(1), indicating nearly ideal cubic close-packing of oxygen atoms. There is exact agreement between the observed a unit-cell dimension and that calculated from the observed Ge-O and Fe-O bond lengths. The cations Ge and Fe are fully ordered at tetrahedral (A) and octahedral (B) sites, respectively, in keeping with synthetic germanate spinels, all of which are fully-ordered normal spinels.

Bederite, a new pegmatite phosphate mineral from Nevados de Palermo, Argentina; description and crystal structure

Abstract Bederite, ideally ⃞Ca2Mn2+2Fe3+2Mn2+2(PO4)6(H2O)2, orthorhombic, a = 12.559(2), b = 12.834(1), c = 11.714(2) Å, V= 1887.8(4) Å3, Z = 4, space group Pcab, is a new mineral from the El Peñón pegmatite, Nevados de Palermo, Salta Province, República Argentina. The mineral occurs as rare ellipsoidal nodules (~5 cm in diameter) enclosed in potassium feldspar or quartz at the core-margin zone of a beryl-type rare-element pegmatite. Associated minerals are quartz, potassium feldspar, muscovite, beryl, columbite, possibly heterosite, and powdery coatings of Mn- and Fe-oxides; in the dumps of the pegmatite, there are numerous other phosphates including altered triphylite-lithiophyllite, arrojadite, eosphorite, laueite, brazilianite, and fairfieldite. Bederite is very dark brown to black with a dark olive-green streak and a vitreous luster. It is brittle with an irregular fracture and a good cleavage parallel to {100}, Mohs hardness is 5, and the observed and calculated densities are 3.48(1) and 3.50 g/cm3, respectively. In transmitted plane-polarized light, bederite is pleochroic X = Y = olive green, Z = brown with X = Y > Z and X = a, Y = c. Z = b. In cross-polarized light, it is biaxial negative with strong dispersion, v > r, 2V(obs) = 54° and 2V(calc) = 60°. Refractive indices are as follows: α = 1.729(3), β = 1.738(3), γ= 1.741(3). Chemical analysis by electron microprobe plus the Penfield method and thermogravimetry gave P2O5 41.76, Al2O3 0.82, Fe2O3 12.00, FeO 2.25, MnO 20.59, MgO 3.45, ZnO 0.40, CaO 10.91, SrO 0.43, Na2O 0.63, H2O 3.52, sum 96.76 wt% where the Fe2O3 and FeO contents were derived from the refined crystal structure. The five strongest lines in the X-ray powder diffraction pattern are as follows: d Å), I, (h k l): 2.768,100, (4 0 2); 2.927, 78, (0 0 4); 3.006, 67, (1 4 1); 2.814, 35, (0 4 2); 2.110, 33, (1 6 0). The crystal structure of bederite was refined to an R index of 2.8% based on 2530 observed (>5σF) reflections measured with MoΚα X-radiation. Bederite is isostructral with wicksite, grischunite, and an unnamed wicksite-like phase; it is related to wicksite by the substitutions Na⃞ + M2Fe3+ → NaNa + M2Mg, M1Mn2+ → M1Fe2+ and M3Mn2+ → M3Fe2+.

Georgeericksenite, Na 6 CaMg(IO 3 ) 6 (CrO 4 ) 2 (H 2 O) 12 , a new mineral from Oficina Chacabuco, Chile; description and crystal structure

Abstract Georgeericksenite, Na6CaMg(IO3)6[(Cr0.84S0.16)O4]2(H2O)12, space group C2/c, a = 23.645(2), b = 10.918(1), c = 15.768(1) Å , β = 114.42(6)°, V = 3707.3(6) Å3, Z = 4, is a new mineral on a museum specimen labeled as originating from Oficina Chacabuco, Chile. It occurs both as isolated and groupings of 0.2 mm sized bright lemon-yellow micronodules of crystals on a host rock principally composed of halite, nitratine, and niter. Associated minerals include plagioclase, clinopyroxene, and an undefined hydrated Ca-K-Ti-iodate-chromate-chloride. Georgeericksenite crystals average 30 × 5 × 5 mm in size and are prismatic to acicular, elongate along [001] and somewhat flattened on {110}, and they have a length-to-width ratio of 6:1. Forms observed are {100}, {110} major, and {2̅33} minor. Crystals are pale yellow, possess a pale-yellow streak, are transparent, brittle, and vitreous, and do not fluoresce under ultraviolet light. The estimated Mohs hardness is between 3 and 4, the calculated density is 3.035 g/cm3, and the mineral is extremely soluble in cold H2O. The optical properties of georgeericksenite are biaxial (+) with α = 1.647(2), β = 1.674(2), γ = 1.704(2), 2 Vcalc = 188.4° and the orientation is Z ≈ c. Pleochroism is slight with X = very pale yellow and Z = distinct yellow-green. The crystal structure of georgeericksenite has been solved by direct methods and refined to an R index of 3.5% using 2019 observed reflections measured with MoKα X-radiation. There is one unique Cr site occupied by 0.84 Cr6+ + 0.16 S and tetrahedrally coordinated by four O atoms, one unique Mg site octahedrally coordinated by O atoms, three unique I sites octahedrally coordinated by O atoms and H2O groups, three unique Na sites with octahedral, augmented octahedral and triangular dodecahedral coordinations, one unique Ca site with square antiprismatic coordination, and six unique (H2O) groups. The cation polyhedra link by corner-, edge-, and face-sharing to form dense heteropolyhedral slabs parallel to (100); these slabs are linked by hydrogen bonding. The formula derived from the crystal-structure refinement is Na6CaMg(IO3)6[(Cr0.84S0.16)O4]2(H2O)12. Crystals of georgeericksenite are extremely unstable under the electron beam during electron microprobe analysis, and the analyzed amounts of all elements fluctuate strongly as a function of time and crystallographic orientation relative to the electron beam. However, extrapolation of the chemical composition to zero time yields values that are in reasonable accord with the chemical formula derived from crystal structure analysis.