Stuart J. Mills

Revised values of the bond valence parameters for [6]Sb(V)-O and [3-11]Sb(III)-O

Abstract Bond valence parameters r0 and b have been re-determined for [3–11]Sb(III)–O and [6]Sb(V)–O, utilising crystal structures of natural and inorganic compounds from the Inorganic Crystal Structure Database. Bond valence parameters for Sb(III) were obtained from a best-fit r0–b curve for 242 independent SbOn polyhedra. For [6]Sb(V), a curve of best fitting r0–b pairs was determined by fitting to 207 independent SbO6 octahedra; b was then determined by optimising bond valence sums on the oxygens of Sb2O5 and Sb2O4, given the limited low quality structural data available for Sb(V) coordination numbers other than 6. Parameter values that minimised r.m.s. deviation from the ideal bond valence sums were r0 = 1.925 Å and b = 0.455 Å for Sb(III) and r0 = 1.904 Å, b = 0.430 Å for [6]Sb(V). The increase in r0 for Sb(III) may represent the repulsive effect of the lone-pair electrons, while the difference in b indicates higher polarisability when these electrons are present. Consideration of subsets of data for differing coordination numbers demonstrates that Sb(III) parameters are applicable to all SbOn coordination numbers (CN = 3–11). We also show that the apparent overbonding using the classical b value cannot be an artefact of unresolved site splitting. For Sb(V), independent determination of b allows bond lengths cautiously to be estimated for CN ≠ 6. This work confirms that the “universal” value b = 0.37 Å is not adequate for heavier cations such as Sb.

Mössbauerite, Fe6 3+ O4 (OH) 8 [CO3]·3H2O, the fully oxidized green rust mineral from Mont Saint-Michel Bay, France

Abstract The new mineral mössbauerite (IMA2012 -049), Fe3+6O4(OH)8[CO3]·3H2O, is a member of the fougèrite group of the hydrotalcite supergroup. Thus, it has a layered double hydroxide-type structure, in which brucite-like layers [Fe3+6+O4(OH)8]2+ are intercalated with CO2-3 anions and water molecules. Mössbauerite is the fully oxidized analogue of fougèrite and trébeurdenite, related to them chemically by the exchange of (Fe3+O2-) with (Fe2+OH-). Mössbauerite, intimately intergrown with trébeurdenite, was discovered in intertidal gleys from Mont Saint-Michel Bay, France, along with quartz, feldspars and clay minerals. Mössbauerite is formed by the oxidation of the other members of the fougèrite group. Like them, it occurs as μm-scale platelets in gleys with restricted access to atmospheric O and decomposes rapidly when exposed to air. Identification and characterization of these minerals has relied on an electrochemical study of synthetic analogues and Mössbauer spectroscopy, which inspired the name of the new mineral. Unlike fougèrite and trébeurdenite, which are blue-green, pure synthetic mössbauerite is orange in colour. Detailed optical and other physical properties could not be determined because of the small platelet size and instability. The hardness is probably 2-3, by analogy with other members of the supergroup and the density, calculated from unit-cell parameters, is 2.950 g/cm3. Synchrotron X-ray data indicate that the natural material is a nanoscale intergrowth of 2T and 3T polytypes; the latter probably has the 3T7 stacking sequence. The corresponding maximum possible space group symmetries are P 3̅m1 and P3m1. Unit-cell parameters for the 3T cell are a = 3.032(7) Å, c = 22.258(4) = 3 x 7.420 Å and Z = ½. Mössbauer spectroscopy at 78 K indicates that two distinct Fe3+ environments exist in a 2:1 ratio. These are interpreted to be ordered within each layer, but without the development of a three- dimensional superlattice. Mössbauerite undergoes gradual magnetic ordering at 70-80 K to a ferromagnetic state, below which it splits into three sextets S1m, S2m and S3m, as measured at 15 K, and shows the same intensity ratio ½:⅙:⅓ as the three doublets for fougèrite D1f, D2f, D3f in the paramagnetic state at 78 K. This suggests that there is also short-range coupling of interlayer carbonate anions with respect to the octahedral layers and that the 2D long-range order of carbonates in interlayers remains unchanged.

IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) Newsletter 26

U. HÅLENIUS (Chairman, CNMNC), F. HATERT (Vice-Chairman, CNMNC), M. PASERO (Vice-Chairman, CNMNC) AND S. J. MILLS (Secretary, CNMNC) 1 Department of Mineralogy, Naturhistoriska Riksmuseet, Box 50007, SE-104 05 Stockholm, Sweden – ulf.halenius@nrm.se 2 Laboratoire de Minéralogie, Université de Liège, B-4000 Liège, Belgium fhatert@ulg.ac.be 3 Dipartimento di Scienze della Terra, Università degli Studi di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy marco.pasero@unipi.it 4 Geosciences, Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia smills@museum.vic.gov.au

Looking for jarosite on Mars: The low-temperature crystal structure of jarosite

Abstract Single-crystal diffraction of jarosite, KFe33+(SO4)2(OH)6, has been undertaken at low temperatures that proxy for martian surface conditions. Room-temperature data are consistent with literature data [a = 7.2913(5), c = 17.1744(17), and V = 790.72(11) in R3̅m], while the first low-temperature data for the mineral is presented (at 253, 213, 173, and 133 K). Data collections between 297 and 133 K show strongly anisotropic thermal expansion, with the c axis much more expandable than the a axis. Much of the anisotropy is due to strong distortion of the KO12 polyhedron, which increases by 8% between 297 and 133 K. The data sets can aid in the identification of jarosite by X‑ray diffraction of martian soils using the Curiosity Rover’s CheMin instrument.

Lead-tellurium oxysalts from Otto Mountain near Baker, California: VII. Chromschieffelinite, Pb10Te6O20(OH)14(CrO4)(H2O)5, the chromate analog of schieffelinite

Abstract Chromschieffelinite, Pb10Te6O20(OH)14(CrO4)(H2O)5, is a new tellurate from Otto Mountain near Baker, California, named as the chromate analog of schieffelinite, Pb10Te6O20(OH)14(SO4)(H2O)5. The new mineral occurs in a single 1 mm vug in a quartz vein. Associated mineral species include: chalcopyrite, chrysocolla, galena, goethite, hematite, khinite, pyrite, and wulfenite. Chromschieffelinite is orthorhombic, space group C2221, a = 9.6646(3), b = 19.4962(8), c = 10.5101(7) Å, V = 1980.33(17) Å3, and Z = 2. Crystals are blocky to tabular on {010} with striations parallel to [001]. The forms observed are {010}, {210}, {120}, {150}, {180}, {212}, and {101}, and crystals reach 0.2 mm in maximum dimension. The color and streak are pale yellow and the luster is adamantine. The Mohs hardness is estimated at 2. The new mineral is brittle with irregular fracture and one perfect cleavage on {010}. The calculated density based on the ideal formula is 5.892 g/cm3. Chromschieffelinite is biaxial (-) with indices of refraction α = 1.930(5), β = 1.960(5), and γ = 1.975(5), measured in white light. The measured 2V is 68(2)°, the dispersion is strong, r < v, and the optical orientation is X = b, Y = c, Z = a. No pleochroism was observed. Electron microprobe analysis provided: PbO 59.42, TeO3 29.08, CrO3 1.86, H2O 6.63 (structure), total 96.99 wt%; the empirical formula (based on 6 Te) is Pb9.65Te6O19.96(OH)14.04(CrO4)0.67(H2O)6.32. The strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 9.814 (020) 100, 3.575 (042,202) 41, 3.347 (222) 44, 3.262 (241,060,113) 53, 3.052 (311) 45, 2.9455 (152,133) 55, 2.0396 (115,353) 33, and 1.6500 (multiple) 33. The crystal structures of schieffelinite (R1 = 0.0282) and chromschieffelinite (R1 = 0.0277) contain isolated Te6+O6 octahedra and Te26+O11 corner-sharing dimers, which are linked into a three-dimensional framework via bonds to Pb2+ atoms. The framework has large channels along c, which contain disordered SO4 or CrO4 groups and H2O. The lone-electron pair of each Pb2+ is stereochemically active, resulting in one-sided Pb-O coordination arrangements. The short Pb-O bonds of the Pb2+ coordinations are all to Te6+O6 octahedra, resulting in strongly bonded layers parallel to {010}, which accounts for the perfect {010} cleavage.

Lead-tellurium oxysalts from Otto Mountain near Baker, California: X. Bairdite, Pb2Cu42+Te26+O10(OH)2(SO4)(H2O), a new mineral with thick HCP layers

Abstract Bairdite, Pb2Cu42+Te26+O10(OH)2(SO4)(H2O), is a new tellurate-sulfate from Otto Mountain near Baker, California, U.S.A. It occurs in vugs in quartz associated with khinite, cerussite, goethite, and hematite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Bairdite is monoclinic, space group P21/c, with unit-cell dimensions a = 14.3126(10), b = 5.2267(3), c = 9.4878(5) Å, b = 106.815(7)°, V = 679.41(7) Å3, and Z = 2. Bairdite occurs as diamond-shaped tabular crystals up to about 250 mm long and 5 mm thick, in subparallel and fan-shaped aggregates. The color is lime green, the streak is pale lime green, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. Bairdite is brittle with an irregular fracture and one perfect cleavage on {100}. The calculated density based on the empirical formula is 6.062 g/cm3. Bairdite is biaxial (+), with calculated indices of refraction of a = 1.953, b = 1.966, and g = 2.039. The measured 2V is 47(2)°, dispersion is r < v, strong and the optical orientation is Y = b; Z ^ a = 34° in obtuse angle b. The pleochroism is strong: Z (pale green) <<< X (green) < Y (green). Electron microprobe analyses (average of 4) provided: PbO 34.22, CaO 0.06, CuO 23.80, TeO3 26.34, SO3 5.74, H2O 2.81 (structure), total 92.97 wt%. The empirical formula (based on 17 O atoms pfu) is: Pb2.05Ca0.01Cu2+3.99Te6+2.00S0.96O17.00H4.16. The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 4.77 (110,102) 50, 4.522 (002,011,111) 66, 3.48 (multiple) 62, 2.999 (311,411) 97, 2.701 (502,113,213) 79, 2.614 (013,020) 100, 1.727 (multiple) 65, and 1.509 (911,033,324) 83. The crystal structure of bairdite (R1 = 0.072 for 1406 reflections with Fo > 4σF) contains edge-sharing chains of Te6+O6 and Cu2+O6 octahedra parallel to b that are joined by corner-sharing in the a direction, forming thick stair-step-like hexagonal close packed layers parallel to {100}. The polyhedral sheet has similarities to those in the structures of timroseite and paratimroseite. The thick interlayer region contains PbO10 polyhedra and half-occupied SO4 groups. Raman and infrared spectral data are presented

IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) Newsletter 25

U. HÅLENIUS (Chairman, CNMNC), F. HATERT (Vice-Chairman, CNMNC), M. PASERO (Vice-Chairman, CNMNC) AND S. J. MILLS (Secretary, CNMNC) 1 Department of Mineralogy, Naturhistoriska Riksmuseet, Box 50007, SE-104 05 Stockholm, Sweden – ulf.halenius@nrm.se 2 Laboratoire de Minéralogie, Université de Liège, B-4000 Liège, Belgium fhatert@ulg.ac.be 3 Dipartimento di Scienze della Terra, Università degli Studi di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy marco.pasero@unipi.it 4 Geosciences, Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia smills@museum.vic.gov.au

Lead-tellurium oxysalts from Otto Mountain near Baker, California: XI. Eckhardite, (Ca,Pb)Cu2+Te6+O5(H2O), a new mineral with HCP stair-step layers

Abstract Eckhardite, (Ca,Pb)Cu2+Te6+O5(H2O), is a new tellurate mineral from Otto Mountain near Baker, California, U.S.A. It occurs in vugs in quartz in association with Br-rich chlorargyrite, gold, housleyite, khinite, markcooperite, and ottoite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Eckhardite is monoclinic, space group P21/n, with unit-cell dimensions a = 8.1606(8), b = 5.3076(6), c = 11.4412(15) Å, β = 101.549(7)°, V = 485.52(10) Å3, and Z = 4. It forms as needles or blades up to about 150 × 15 × 5 mm in size, typically in radial or sub-radial aggregates, but also as isolated needles. The color is light bluish green and the streak is very pale bluish green. Crystals are transparent with vitreous to subadamantine luster. The Mohs hardness is estimated at between 2 and 3. Eckhardite is brittle with an irregular fracture and one likely (but not observed) cleavage on {101}. The calculated density based on the empirical formula is 4.644 g/cm3. The mineral is biaxial (-), with indices of refraction of α = 1. 770 (calc), β = 1.860 (calc), and γ = 1.895(5). The measured 2V is 61.2(5)°, dispersion is r < v, perceptible and the optical orientation is Z = b; X ≈ [101]. The pleochroism is: Z (light blue green) < Y (very pale blue green) < X (colorless). The normalized electron microprobe analyses (average of 4) provided: PbO 4.79, CaO 15.90, MgO 0.06, CuO 22.74, Fe2O3 0.06, TeO3 51.01, H2O 5.45 (structure), total 100 wt%. The empirical formula (based on 6 O apfu) is: Ca0.962Pb0.073Cu2+0.971Mg0.005Fe3+0.002Te6+0.986 O6H2.052. The Raman spectrum exhibits prominent features consistent with the mineral being a tellurate, as well as an OH stretching feature confirming a hydrous component. The eight strongest powder X‑ray diffraction lines are [dobs in Å (hkl) I]: 5.94 (101) 100, 3.287 (112) 80, 2.645 (020,2̅13) 89, 2.485 (1̅14,301,014) 48, 2.245 (114,122) 46, 1.809 (223,4̅13,321,4̅04) 40, 1.522 (413,5̅12,421,133) 42, and 1.53 (2̅17,2̅33,4̅06) 43. The crystal structure of eckhardite (R1 = 0.046 for 586 reflections with Fo > 4σF) consists of stair-step-like octahedral layers of Te6+O6 and Cu2+O6 octahedra parallel to {101}, which are linked in the [101̅] direction by bonds to interlayer Ca atoms. The structure can be described as a stacking of stepped HCP layers alternating with chains of CaO7 polyhedra. The structures of bairdite, timroseite, and paratimroseite also contain stair-step-like HCP polyhedral layers.

Lead-tellurium oxysalts from Otto Mountain near Baker, California: IX. Agaite, Pb3Cu2+Te6+O5(OH)2(CO3), a new mineral with CuO5-TeO6 polyhedral sheets

Abstract Agaite, Pb3Cu2+Te6+O5(OH)2(CO3), is a new tellurate from the Aga mine on Otto Mountain near Baker, California, U.S.A. The new mineral is known from only one specimen. It occurs on quartz in association with cerussite, Br-rich chlorargyrite, chrysocolla, goethite, khinite, markcooperite, muscovite, phosphohedyphane, timroseite, and wulfenite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Agaite is orthorhombic, space group Pca21, with unit-cell dimensions a = 10.6522(7), b = 9.1630(5), c = 9.6011(7) Å, V = 937.12(11) Å3, and Z = 4. Agaite crystals form as blades flattened on {010} and probably elongated on [001], and are up to about 20 μm thick and 200 μm in length. The color is blue, the streak is pale blue, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. Agaite is brittle with an irregular fracture and one perfect cleavage on {010}. The calculated density based on the empirical formula is 6.987 g/cm3. Agaite is biaxial (-), with calculated indices of refraction of α = 2.015, β = 2.065, and γ = 2.070°. The measured 2V is 34(5)° and the optical orientation is X = b, Y = c, and Z = a. It is pleochroic: X = pale blue, Y and Z = blue; X < Y = Z. Electron microprobe analyses (average of 4) provided: PbO 65.91, CuO 7.75, TeO3 17.41, CO2 4.33 (structure), H2O 1.78 (structure), total 97.18 wt%. The empirical formula (based on 10 O apfu) is: Pb3.00Cu2+0.99Te6+ 1.01O5(OH)2(CO3). The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 4.26 (012) 28, 4.165 (211) 14, 3.303 (022, 310, 221) 100, 2.7472 (131, 203, 312) 68, 2.571 (032, 401, 231) 14, 2.0814 (332, 422) 21, 2.0306 (511) 17, and 1.7468 (multiple) 40. The crystal structure of agaite (R1 = 0.033 for 1913 reflections with Fo > 4σF) contains edge-sharing chains of Cu2+O5 square pyramids and Te6+O6 octahedra parallel to a that are joined by corner-sharing in the c direction, forming a polyhedral sheet parallel to {010}. The polyhedral sheet is very similar to those in the structures of timroseite and paratimroseite. The thick interlayer region contains 8- and 9-coordinated Pb2+, as well as CO3 and OH groups. The Pb coordinations have lopsided distributions of bond lengths attributable to the localization of the Pb2+ 6s2 lone-pair electrons.

Lead-tellurium oxysalts from Otto Mountain near Baker, California: VIII. Fuettererite, Pb3Cu62+Te6+O6(OH)7Cl5, a new mineral with double spangolite-type sheets

Abstract Fuettererite, Pb3Cu62+Te6+O6(OH)7Cl5, is a new tellurate from Otto Mountain near Baker, California, named for Otto Fuetterer who is largely responsible for the development of the mining claims on Otto Mountain. The new mineral is known from only two specimens, one from the NE2 vein and the other from the Bird Nest drift. Fuettererite occurs in vugs in quartz, on the first specimen associated with Br-rich chlorargyrite, iodargyrite, and telluroperite and on the second specimen associated with anglesite, anatacamite, atacamite, chalcopyrite, galena, goethite, hematite, muscovite, phosphohedyphane, timroseite, and wulfenite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Fuettererite is hexagonal, with space group R3̄, a = 8.4035(12), c = 44.681(4) Å, V = 2732.6(6) Å3, and Z = 6. Crystals are tabular to short prismatic, exhibit the forms {100}, {101}, and {001} and reach a maximum dimension of 50 μm. The color is bluish green, the streak is pale bluish-green, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. The new mineral is brittle with irregular fracture and one perfect cleavage on {001}. The calculated density based on the empirical formula is 5.528 g/ cm3. Fuettererite is uniaxial (-), with calculated indices of refraction of ω = 2.04 and ε = 1.97, and is dichroic bluish-green, E < O. Electron microprobe analysis provided: PbO 41.45, CuO 30.35, Al2O3 0.23, TeO3 12.80, Cl 12.08, H2O 3.55 (structure), O=Cl -2.73, total 97.73 wt%. The empirical formula (based on 18 O + Cl apfu) is: Pb2.88Cu2+5.92Al0.07Te6+ 1.13O6.59(OH)6.12Cl5.29. The ten strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 6.106 (104) 44, 3.733 (0.0.12) 100, 2.749 (121̄) 53, 2.6686 (124̄) 49, 2.5289 (127̄) 41, 2.2772 (1.2.11) 38, 1.9637 (315, 1.2.1̄6̅) 87, 1.8999 (multiple) 48, 1.5976 (multiple) 40, and 1.5843 (410, 1.2.23, 143) 44. The crystal structure of fuettererite (R1 = 0.031 for 971 reflections with Fo > 4σF) contains edge-sharing sheets of CuO5Cl and TeO6 octahedra. These sheets are virtually identical to that in the structure of spangolite, but in fuettererite they are linked together to form a double sheet. The double octahedral sheets alternate with thick double layers of PbO2Cl6 polyhedra. The CuO5Cl octahedra exhibit pronounced Jahn-Teller distortions and the PbO2Cl6 polyhedron has a lopsided distribution of bond lengths attributable to the localization of the Pb2+ 6s2 lone-pair electrons.