Alan J. Criddle

Tripuhyite, FeSbO4, revisited

Abstract The exact nature of tripuhyite remains controversial more than 100 years after the first description of the mineral. Different stoichiometries and crystal structures (rutile or tri-rutile types) have been suggested for this Fe-Sb-oxide. To address these uncertainties, we studied tripuhyite from Tripuhy, Minas Gerais, Brazil (type material) and Falotta, Grisons, Switzerland using single-crystal and powder X-ray diffraction (XRD), optical microscopy and electron microprobe analysis. Electron microprobe analyses showed the Fe/Sb ratios to be close to one in tripuhyite from both localities. Single crystal XRD studies revealed that tripuhyite fromthe type locality and fromFalotta have the rutile structure (P42/mnm, a = 4.625(4) c = 3.059(5) and a = 4.6433(10) c = 3.0815(9) Å , respectively). Despite careful examination, no evidence for a tripled c parameter, characteristic of the tri-rutile structure, was found and hence the structure was refined with the rutile model and complete Fe-Sb disorder over the cationic sites in both cases (type material: R1 = 3.61%; Falotta material: R1 = 3.96%). The specular reflectance values of type material tripuhyite and lewisite were measured and the following refractive indices calculated (after Koenigsberger): tripuhyite nmin = 2.14, nmax = 2.27; lewisite (cubic) n = 2.04. These results, together with those of 57Fe and 121Sb Mössbauer spectroscopy on natural and synthetic tripuhyites reported in the literature, indicate that the chemical formula of tripuhyite is Fe3+Sb5+O4 (FeSbO4). Thus, tripuhyite can no longer be attributed to the tapiolite group of minerals of general type AB2O6. A comparison of the results presented with the mineralogical data of squawcreekite suggests that tripuhyite and squawcreekite are identical. In consequence, tripuhyite was redefined as Fe3+Sb5+O4 with a rutile-type structure. Both the proposed new formula and unit cell (rutile-type) of tripuhyite as well as the discreditation of squawcreekite have been approved by the Commission on New Mineral and Mineral Names (CNMMN) of the International Mineralogical Association (IMA).

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.

A new mineral, chrisstanleyite, Ag2Pd3Se4, from Hope's Nose, Torquay, Devon, England

Abstract Chrisstanleyite, Ag2Pd3Se4, is a new mineral from gold-bearing carbonate veins in Middle Devonian limestones at Hopes Nose, Torquay, Devon, England. It is associated with palladian and argentian gold, fischesserite, clausthalite, eucairite, tiemannite, umangite, a Pd arsenide-antimonide (possibly mertieite II), cerussite, calcite and bromian chlorargyrite. Also present in the assemblage is a phase similar to oosterboschite, and two unknown minerals with the compositions, PdSe2 and HgPd2Se3. Chrisstanleyite occurs as composite grains of anhedral crystals ranging from a few lam to several hundred μm in size. It is opaque, has a metallic lustre and a black streak, VHN100 ranges from 371-421, mean 395 kp/mm2 (15 indentations), roughly approximating to a Mohs hardness of 5. Dcalc = 8.308 g/cm3 for the ideal formula with Z = 2. In plane-polarised reflected light, the mineral is very slightly pleochroic from very light buff to slightly grey-green buff, is weakly bireflectant and has no internal reflections. Bireflectance is weak to moderate (higher in oil). Anisotropy is moderate and rotation tints vary from rose-brown to grey-green to pale bluish grey to dark steel-blue. Polysynthetic twinning is characteristic of the mineral. Reflectance spectra and colour values are tabulated. Very little variation was noted in eleven electron-microprobe analyses on five grains, the mean is: Ag 25.3, Cu 0.17, Pd 37.5, Se 36.4, total 99.37 wt.%. The empirical formula (on the basis of ∑M + Se = 9) is (Ag2.01Cu0.02)∑2.03 Pd3.02Se3.95, ideally Ag2Pd3Se4 . Chrisstanleyite is monoclinic, a 6.350(6), b 10.387(4), c 5.683(3) Å, β 114.90(5)° space group P21/m (11) or P21(4). The five strongest X-ray powder-diffraction lines [d in Å (I)(hkl)] are: 2.742 (100) (-121), 2.688 (80) (-221), 2.367 (50) (140), 1.956 (100) (-321,150) and 1.829 (30) (-321,042). The name is in honour of Dr Chris J. Stanley of The Natural History Museum in London. The mineral and its name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.

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.

Mereheadite, Pb 2 O(OH)Cl; a new litharge-related oxychloride from Merehead Quarry, Cranmore, Somerset

Abstract Mereheadite, ideally Pb2O(OH)Cl, is a new mineral related to litharge and which is structurally similar to synthetic bismuth-oxyhalides. With other lead- and lead-copper oxychlorides, it occupies lenses and cavities in veins of manganese and iron oxide minerals which cut through a sequence of dolomitic limestones at Merehead quarry, Cranmore, Somerset (51°12ʹN, 2°26ʹW). Mereheadite is pale yellow to reddish-orange, transparent to translucent and has a white streak and a vitreous or resinous lustre. It is not fluorescent. Individual grains, up to a few mm across, cluster together in compact masses of 10−30 mm in size, but discrete crystals have not been observed. Specular reflectance data on randomly orientated grains from 400 to 700 nm are provided, and refractive indices calculated from these at 590 nm range from 2.19 to 2.28. H= 3.5, VHN100 = 171, D(meas) = 7.12(10) g/cm3, Dcalc = 7.31 g/cm3. The mineral is brittle with an uneven, conchoidal to hackly fracture and has a perfect (001) cleavage which is parallel to the sheets of PbO and Cl. It is intimately associated with mendipite, blixite, cerussite, hydrocerussite and calcite in lenses and pods in the veins. Other minerals which occupy cavities in these veins include chloroxiphite, paralaurionite, parkinsonite and the borosilicate datolite. Mereheadite is monoclinic, space group C2/c, and its cell parameters, refined from powder X-ray diffraction are: a = 5.680(2), b = 5.565(3), c = 13.143(9) Å, β= 90.64(4)°,V = 415.4 (8)Å3, Z = 4. The ten strongest reflections in the X-ray powder diffraction pattern are [d in Å, (I, hk/)]: 2.930(10,113), 3.785(5,111,-111), 2.825(4,200), 6.581(4,002), 2.182(4,115), 2.780(4,020), 3.267(4,004), 1.980(3,−220), 1.695(3,224,132,117), 1.716(3,026). Its empirical formula is Pb8O4.19(BO3)0.51 (CO3)0.62(OH)0.76Cl4.09. Although it is very similar chemically to blixite, it has notably different cell parameters. There is some uncertainty about the essential nature of boron and carbon in natural mereheadite. This stems from the impossibility of ensuring the purity of samples for wet-chemical analysis, and from the predominance of lead in the structure of the mineral which has meant that the location of boron and carbon within the mereheadite structure is unresolved, 11B MAS NMR does show, however, that boron is present as BO3 groups. The structure consists of alternating PbO sheets and layers of chlorine atoms. Each lead atom is coordinated to four chlorines and four O/OH in a square antiprism configuration. As such, it is structurally-related to nadorite, thorikosite and schwartzembergite. Comparisons with structurally analogous phases such as bismuth oxychlorides and bismutite (Bi2O2CO3) suggest that the BO3 and CO3 groups are likely to replace chlorine in the layer between PbO sheets. The composition of natural mereheadite is defined by three end-members: the mereheadite end-member Pb2O(OH)Cl, and two fictive end-members Pb2(OH)2CO3 and Pb2(OH)2CO3.

The new mineral baumstarkite and a structural reinvestigation of aramayoite and miargyrite

Abstract Baumstarkite is a new mineral found coating miargyrite from the San Genaro mine, Huancavelica Department, Peru. It is triclinic and the third naturally occurring modification of AgSbS2 besides monoclinic miargyrite and cubic cuboargyrite. The composition is usually close to the ideal formula. However, some grains of baumstarkite show zoned lamellae with As contents up to 11.5 wt% and accords to Ag3(Sb,As)2SbS6. Baumstarkite is isotypic with aramayoite [end-member composition Ag3Sb2BiS6; solid solutions require the extended formula Ag3Sb2(Bi,Sb)S6]. Single-crystal X-ray structure investigations were performed for baumstarkite [type locality, a = 7.766(2), b = 8.322(2), c = 8.814(2) Å, α = 100.62(2), β = 104.03(2), γ = 90.22(2)°, Z = 2{Ag3Sb3S6}, space group P1̅, R1(F) = 0.057, wR2(F2) = 0.128], aramayoite [Armonia mine, El Quevar, Argentinia: a = 7.813(2), b = 8.268(2), c = 8.880(2) Å, α = 100.32(2), β = 104.07(2), γ = 90.18(2)°, Z = 2{Ag3Sb2S6}, space group P1̅, R1(F) = 0.034, wR2(F2) = 0.084], and miargyrite associated with baumstarkite type material [a = 12.862(3), b = 4.409(1), c = 13.218(3) Å, β = 98.48(2)°, Z = 8{AgSbS2}, space group C2/c, R1(F) = 0.031, wR2(F2) = 0.082]. The space-group symmetries of aramayoite and miargyrite were revised, and the refinements unambiguously showed that the three investigated minerals are centrosymmetric. In baumstarkite and aramayoite each three atomic sites are occupied by Ag and M = As, Sb, Bi, respectively. The Ag atoms have two short bonded ligands (Ag-S is 2.51 to 2.58 Å). The M1 and M2 sites are [3 + 3] coordinated and are predominantly occupied by (Sb, As) atoms (M-S = 2.44 to 2.54 Å and > 3.09 Å). The [2 + 2 + 2] coordination of the M3 atom differs in the two mineral species: the two shortest bond lengths in baumstarkite are smaller (2.51 Å) than in aramayoite (2.64 Å) to allow for the different sizes of the Sb and Bi atoms, respectively; the medium bond lengths are similar (2.75 to 2.82 Å) and the longest bond lengths are > 3.02 Å. Considering only the nearest-neighbor environments, baumstarkite and aramayoite feature zigzag chains parallel to [010], which are linked together to form layers parallel to (001). In miargyrite [2 + 2] and [2] coordinated Ag atoms are linked by SbS3 pyramids to form a three-dimensional network.

Paganoite, NiBi 3+ As 5+ O 5 , a new mineral from Johanngeorgenstadt, Saxony, Germany: description and crystal structure

Paganoite, ideally NiBi 3+ As 5+ O 5 , triclinic space group P1, a = 6.7127(8), b = 6.8293(8), c = 5.2345(6) A, α = 107.625(2)°, β = 95.409(2)°, γ = 111.158(2)°, V = 207.62 A 3 , a:b:c: = 0.9829:1:0.7665, Z = 2, is a new mineral found on a single nickeline-veined quartz specimen from Johanngeorgenstadt, Saxony, Germany. The strongest seven lines of the X-ray powder-diffraction pattern [ d in A ( hkl )] are: 5.943 (100) (010); 3.233 (100) (011); 3.067 (60) (021); 3.047 (50) (200); 2.116 (50) (112,031, 311,122,231); 2.095 (40) (230,102); 1.659 (40) (420). It occurs as isolated orange-brown to deep-golden-brown crystals and crystal aggregates which are always intimately associated with aerugite; additional associations include bunsenite, xanthiosite, rooseveltite, native bismuth and two undefined arsenates. Individual prismatic crystals are subhedral to euhedral, elongate along [010] with a length-to-width ratio of 3:1, and average 0.3 mm in longest dimension. Forms observed are {100} major, {010} minor, {001} minor and perhaps { hOl } minor. Crystals possess a very pale orange-brown streak, are transparent (crystals) to translucent (aggregates), brittle, adamantine (almost gemmy), and do not fluoresce under ultraviolet light. The mineral shows neither twinning nor cleavage, has an uneven fracture, and the calculated density (for the empirical formula) is 6.715 g/cm 3 . Electron-microprobe analyses yielded NiO 15.37, CoO 2.05, Bi 2 O 3 55.06, As 2 O 5 28.0, total 100.48 wt.% The empirical formula, derived from the crystal-structure analysis and electron-microprobe analyses, is (Ni 2+ 0.86 C 2+ 0.11 ) Σ0.97 Bi 3+ 0.99 As 5+ 1.02 O 5 , based on O = 5. In reflected plane-polarized light in air, it is grey with no obvious internal reflections, bireflectance or pleochroism. Measured reflectance values, in air and in oil, are tabulated: indices of refraction calculated from these at 589 nm are 2.07 and 2.09. The name honours Renato and Adriana Pagano for their long-standing service to the European mineralogical community. The crystal structure of paganoite has been solved by direct methods and refined on the basis of F 2 using 977 unique reflections measured with Mo K α X-radiation on a diffractometer equipped with a CCD-based detector. The final R 1 was 4.4%, calculated for the 926 observed reflections. The structure contains AsO 4 tetrahedra and distorted Ni 2+ O 6 octahedra, as well as one-sided Bi 3+ O 5 polyhedra due to the presence of an s 2 lone pair of electrons on the Bi 3+ cation. The structure is an open framework composed of dimers of edge-sharing NiO 6 octahedra that are linked by vertex-sharing with AsO 4 tetrahedra. Bi 3+ cations occur within voids in the framework, and bond only to framework elements. The structure of paganoite is very closely related to that of jagowerite, BaAl 2 P 2 O 8 (OH) 2 , which possesses an identical framework of octahedra and tetrahedra.

Feinglosite, a new mineral related to brackebuschite, from Tsumeb, Namibia

Abstract Feinglosite, the zinc analogue of arsenbrackebuschite, was found lining a cavity in a sample of massive chalcocite from Tsumeb, Namibia. In this cavity it is associated with wulfenite, anglesite and goethite. The mean of seven electron-microprobe analyses (wt.%) is: PbO 61.4, ZnO 7.3, FeO 1.8, As2O5 22.1, SO3 5.3, H2O (by difference) [2.1], total = [100.00]%, leading to the ideal formula: Pb2(Zn,Fe)[(As,S)O4]·H2O. Feinglosite is monoclinic, space group P21 or P21/m, a 8.973(6), b 5.955(3), c 7.766(6) Å, β 112.20(6)°, with Z = 2. The strongest five reflections of the X-ray powder diffraction pattern are [d in Å (I) (hkl)]: 4.85 (50) (110), 3.246 (100) (112), 2.988 (60) (301), 2.769 (60) (300/211), 2.107 (50) (321). The mineral is pale olive-green, transparent, sectile, and has a white streak and adamantine lustre. It overgrows clusters of goethite crystals and forms globular microcrystalline aggregates up to 0.5-0.75mm in size. The hardness on Mohs‘ scale is 4-5: the mean micro-indentation hardness is 263 at VHN100. Its calculated density is 6.52 g cm−3. The mineral is pale brownish grey in reflected light (when compared with goethite). Visible spectrum reflectance data are presented. Feinglosite is named for Mark N. Feinglos who first recognised the mineral on a specimen in his collection.

Suredaite, PbSnS3, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina: mineralogy and crystal structure

Abstract Suredaite, ideally PbSnS3, is a new mineral species from the Pirquitas Ag-Sn deposit (Province Jujuy, NW-Argentina). It was observed in symmetrically banded veins in the Oploca district, and is associated with sphalerite, arsenopyrite, pyrite-marcasite, cassiterite, cylindrite, franckeite, hocartite, rhodostannite, and various Ag-Sb and Ag-Bi sulfosalts in minor amounts. Suredaite occurs in layers up to 1 cm in thickness as aggregates of radially arranged tabular-prismatic (single) crystals, has a metallic lustre, and a dark grey streak. VHN50 ranges between 18.2 and 20.6 (mean 19.6) GPa, the Mohs hardness is 2.5-3. It has perfect cleavages parallel to {001}, {101}, and {100}. The measured density varies between 5.54 and 5.88 g/cm3, Dx was determined to be 5.615 g/cm3. In reflected plane-polarised light, it is white and is not perceptibly bireflectant or pleochroic. It lacks internal reflections and is weakly anisotropic with metallic blue, mauve to brown rotation tints. Specular reflectance percentages in air and in oil are tabulated from 400 to 700 nm and compared graphically with those for the type specimen of teallite, PbSnS2. Electron microprobe analyses showed suredaite to be chemically inhomogeneous with respect to the compositional variations (in wt%): Pb 42.3- 48.5, Ag 0.3-1.1, Fe 0.3-1.0, As 0.2-2.1, Sn 27.7-30.2, S 23.1-24.7. The crystal structure determined from single-crystal X-ray diffraction data revealed orthorhombic symmetry [space group Pnma, Z = 4, a = 8.8221(3), b = 3.7728(3), c = 14.0076(3) Å; V = 466.23(4) Å3]. The atomic arrangement is isostructural to the NH4CdCl3 structure type which exists in a series of isotypic sulfides and selenide compounds. The suredaite structure, which is the natural analogue of synthetic PbSnS3, consists of columns of double-edge sharing octahedra running parallel to the b axis, which house the Sn atoms. These columns are linked by rods of eightfold-coordinated Pb atoms. On the basis of the structure determination, the empirically determined idealized formula follows a [8](Pb, As,Ag, Sn) [6](Sn,Fe)S3 stoichiometry. Crystalchemical arguments suggest Ag possibly to occupy interstitial sites according to the alternative formula [4](⃞,Ag) [8](Pb, As, Sn) [6](Sn,Fe) S3. The name of this new mineral species is in honor of R.J. Sureda Leston, head of the Department of Mineralogy and Economic Geology, University of Salta, Argentina.

TRACE-ELEMENTS IN PLATINUM-GROUP MINERALS STUDIED USING NUCLEAR MICROSCOPY

Abstract A combination of μ-PIXE and μ-RBS has been used to study concentrations and distributions of trace elements in platinum group minerals from eluvial and alluvial deposits from the western seaboard of North America. Thirteen of the pure element standards, used in the EPMA investigation, were first analysed by μ-PIXE. These analyses were used to establish limits of confidence in the analytical technique. It is shown that using simultaneous RBS to determine the matrix composition and incident charge accurate PIXE analysis is possible without standards. Natural grains of Pt-Fe and Os-Ir-Ru alloys were then analysed and traces of Cu, Fe, Ni, Ti, Ru, Rh, Pd, Cr, etc., were determined at levels ranging from 80 ppm to 5000 ppm. It is shown that while there may be minor variations between localities, the trace element distribution within the grains studied is essentially uniform.