ALBERT

Description: 〈span〉Fanfaniite, Ca〈sub〉4〈/sub〉Mn〈sup〉2+〈/sup〉Al〈sub〉4〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉6〈/sub〉(OH,F)〈sub〉4〈/sub〉·12H〈sub〉2〈/sub〉O, is a new secondary phosphate mineral from the Foote spodumene mine, North Carolina, USA and the Hagendorf-Süd pegmatite, Bavaria, Germany. At the Foote mine, it forms radial aggregates up to 0.5 mm in diameter of colourless, transparent, thin blades, flattened on {010} and elongated on [001], associated with whiteite-(CaMnMn). At Hagendorf-Süd, the mineral occurs as isolated very thin laths on the surface of fibrous spheroids of kayrobertsonite and is associated with altered triplite–zwieselite and whiteite-(CaMnMn). The measured density (Foote mine) is 2.58(2) g cm〈sup〉−3〈/sup〉. Optically, fanfaniite (Foote mine) is biaxial (–), with α = 1.573(2), β = 1.582(2), γ = 1.585(2) and 2〈span〉V〈/span〉(meas) = 57(1)°. Dispersion was not observed. The optical orientation is: 〈span〉Z〈/span〉 = 〈strong〉b〈/strong〉, 〈span〉X〈/span〉 ^ 〈strong〉c〈/strong〉 ≈ 40° in β obtuse. Pleochroism was not evident. Electron microprobe analyses gave the empirical formulas Ca〈sub〉3.91〈/sub〉Mn0.772+Mg〈sub〉0.10〈/sub〉Zn〈sub〉0.02〈/sub〉Al〈sub〉3.89〈/sub〉Fe0.213+(PO〈sub〉4〈/sub〉)〈sub〉6〈/sub〉(OH)〈sub〉3.90〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉12.10〈/sub〉 (Foote mine) and Ca〈sub〉3.73〈/sub〉Mn0.762+Mg〈sub〉0.25〈/sub〉Zn〈sub〉0.08〈/sub〉Al〈sub〉3.89〈/sub〉Fe0.293+(PO〈sub〉4〈/sub〉)〈sub〉6〈/sub〉F〈sub〉1.10〈/sub〉(OH)〈sub〉3.08〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉11.82〈/sub〉 (Hagendorf-Süd). Fanfaniite has monoclinic symmetry, space group 〈span〉C〈/span〉2/〈span〉c〈/span〉, with 〈span〉a〈/span〉 = 10.021(4) Å, 〈span〉b〈/span〉 = 24.137(5) Å, 〈span〉c〈/span〉 = 6.226(3) Å, β = 91.54(2)° and 〈span〉V〈/span〉 = 1505(1) Å〈sup〉3〈/sup〉. The crystal structure was refined to 〈span〉R〈/span〉〈sub〉obs〈/sub〉 = 0.043 for 1909 unique reflections to a resolution of 0.7 Å. Fanfaniite is the Mn〈sup〉2+〈/sup〉-dominant analogue of montgomeryite. The name honours Luca Fanfani who structurally characterised many phosphate minerals including montgomeryite.〈/span〉

Description: 〈span〉The crystal structure of segelerite, Ca〈sub〉2〈/sub〉Mg〈sub〉2〈/sub〉Fe1.43+Al〈sub〉0.6〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉4〈/sub〉(OH)〈sub〉2〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉8〈/sub〉, from the Mount Deverell variscite deposit, Western Australia, has been refined using single-crystal X-ray data to 〈span〉wR〈/span〉〈sub〉obs〈/sub〉 = 0.048 for 2082 unique reflections and all H atoms were located during the refinement. Cell parameters are 〈span〉a〈/span〉 = 14.7772(2) Å, 〈span〉b〈/span〉 = 18.7079(2) Å, 〈span〉c〈/span〉 = 7.2424(1) Å, space group 〈span〉Pbca〈/span〉. The H-bonding scheme is described and compared to that for the combinatorial polymorph, jahnsite. The crystal structures of both minerals comprise heteropolyhedral slabs of composition [〈span〉XM〈/span〉1Fe23+(OH)〈sub〉2〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉4〈/sub〉], that are linked together 〈span〉via〈/span〉 corner-sharing of PO〈sub〉4〈/sub〉 tetrahedra with isolated [〈span〉M〈/span〉2(O〈sub〉p〈/sub〉)〈sub〉2〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉4〈/sub〉] octahedra. The structures differ in the mode of linkage of the 〈span〉M〈/span〉2 octahedra, which is 〈span〉via trans〈/span〉 O〈sub〉p〈/sub〉 ligands in segelerite and 〈span〉via〈/span〉 both 〈span〉trans〈/span〉 and 〈span〉cis〈/span〉 O〈sub〉p〈/sub〉 ligands in jahnsite. In segelerite, 〈span〉X〈/span〉 = 〈span〉M〈/span〉1 = Ca, whereas in jahnsite-group minerals, 〈span〉X〈/span〉 = Ca, Na, Mn〈sup〉2+〈/sup〉 and 〈span〉M〈/span〉1 = Mn〈sup〉2+〈/sup〉, Mg〈sup〉2+〈/sup〉, Fe〈sup〉2+〈/sup〉, Fe〈sup〉3+〈/sup〉. 〈span〉X〈/span〉 and 〈span〉M〈/span〉1 alternate along the 7 Å axis and it is proposed that different magnitudes of rotation of the Fe〈sup〉3+〈/sup〉 octahedra about the 7 Å axis to accommodate the different coordination requirements of the 〈span〉X〈/span〉 and 〈span〉M〈/span〉1 cations drives the symmetry changes in the two minerals so that a strong H-bonding network is maintained.〈/span〉

Description: 〈span〉The new lead oxychloride vanadate mineral erikjonssonite was discovered at the abandoned Kombat copper mine, Grootfontein district, Namibia, in association with hausmannite, calcite, glaucochroite, baryte, cerussite, and an insufficiently studied mineral chemically related to kombatite. Erikjonssonite forms thick tabular orange-red grains up to 0.3 × 0.5 × 0.5 mm〈sup〉3〈/sup〉. The new mineral is brittle, has Mohs’ hardness of 2½ and an uneven fracture. Distinct cleavage on (010) is observed. 〈span〉D〈/span〉〈sub〉calc〈/sub〉 = 7.967 g/cm〈sup〉3〈/sup〉. The reflectance values [〈span〉R〈/span〉〈sub〉max〈/sub〉, %/〈span〉R〈/span〉〈sub〉min〈/sub〉, % (λ, nm)] are: 20.4/18.9 (470), 19.0/17.6 (540), 18.5/17.1 (589), 18.0/16.6 (650). The infrared spectrum shows the absence of H-, C- and B-bearing groups. The chemical composition is (wavelength-dispersive mode electron microprobe, wt%): SiO〈sub〉2〈/sub〉 0.86, V〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 1.73, As〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 0.96, MoO〈sub〉3〈/sub〉 1.70, PbO 92.54, Cl 4.15, –O=Cl −0.94, total 101.00. The empirical formula based on 46 O + Cl atoms per formula unit (〈span〉apfu〈/span〉) is Pb〈sub〉31.50〈/sub〉(V1.455+Si1.09Mo0.906+As0.635+)〈sub〉Σ4.07〈/sub〉Cl〈sub〉8.89〈/sub〉O〈sub〉37.11〈/sub〉. The simplified formula is {(Pb〈sub〉32〈/sub〉O〈sub〉21〈/sub〉)[(V,Si,Mo,As)O〈sub〉4〈/sub〉]〈sub〉4〈/sub〉}Cl〈sub〉9〈/sub〉. The crystal structure has been refined to 〈span〉R〈/span〉 = 4.3% based on 7730 independent reflections with 〈span〉I〈/span〉 〉 2σ(〈span〉I〈/span〉). Erikjonssonite is monoclinic, 〈span〉C〈/span〉2/〈span〉c〈/span〉, 〈span〉a〈/span〉 = 23.200(5), 〈span〉b〈/span〉 = 22.708(5), 〈span〉c〈/span〉 = 12.418(3) Å, β = 102.167(4)°, 〈span〉V〈/span〉 = 6395(2) Å〈sup〉3〈/sup〉, and 〈span〉Z〈/span〉 = 4. The structure of erikjonssonite is very similar to that of hereroite: in both minerals two [Pb〈sub〉32〈/sub〉O〈sub〉21〈/sub〉]〈sup〉22+〈/sup〉 oxocentred blocks formed by OPb〈sub〉4〈/sub〉 tetrahedra with inserted TO〈sub〉4〈/sub〉 tetrahedral groups alternate with one chloride sheet. Average 〈T–O〉 bond lengths in the tetrahedral groups demonstrate very similar values which is interpreted as both T1 and T2 sites having mixed occupancies of V〈sup〉5+〈/sup〉, Si〈sup〉4+〈/sup〉, Mo〈sup〉6+〈/sup〉 and As〈sup〉5+〈/sup〉, unlike hereroite where 〈T–O〉 bond lengths are different and one site is exclusively occupied by As〈sup〉5+〈/sup〉. The strongest lines of the powder X-ray diffraction pattern [〈span〉d〈/span〉, Å (〈span〉I〈/span〉, %) (〈span〉hkl〈/span〉)] are: 3.501 (24) (531, 2¯61), 2.980 (100) (551, 2¯24), 2.794 (45) (8¯02, 5¯14), 1.990 (24) (8¯82), 1.977 (21) (6¯06), 1.762 (20) (715, 8¯.10.2, 10.6.2), 1.648 (33) (1¯1.5.5). The mineral is named in honour of the Swedish mineralogist Erik Jonsson (b. 1967). The holotype material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia. The concept of a “defect number (DN)” which is the number of O〈sup〉2–〈/sup〉 ions removed from the ideal [PbO] block per cavity area is suggested in order to classify the layered Pb oxychloride minerals structurally related to litharge.〈/span〉

Description: 〈span〉Milanriederite, a new vesuvianite-group mineral, was discovered in the Kombat deposit, Grootfontein district, Otjozondjupa region, Namibia, in association with baryte, calcite, jacobsite, hausmannite, glaucochroite and native copper. The new mineral forms dark brownish-red dipyramidal crystals up to 3 mm across. The major crystal form is {111} and the minor forms are {001}, {110}, and {100}. Milanriederite is brittle, has a Mohs’ hardness of six and an uneven fracture. Neither cleavage nor parting is observed. 〈span〉D〈/span〉〈sub〉meas〈/sub〉 = 3.53(2) g/cm〈sup〉3〈/sup〉, 〈span〉D〈/span〉〈sub〉calc〈/sub〉 = 3.547 g/cm〈sup〉3〈/sup〉. The new mineral is optically uniaxial (–), ω = 1.744(3), ε = 1.737(3). The infrared (IR) spectrum of milanriederite significantly differs from IR spectra of other vesuvianite-group minerals. According to Mössbauer data, all iron in the mineral is trivalent. The chemical composition is (electron microprobe, H〈sub〉2〈/sub〉O determined by gas chromatography of ignition products, wt%): Na〈sub〉2〈/sub〉O 0.47, MgO 5.49, CaO 29.86, Mn〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 1.40, Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 9.75, Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 6.03, Y〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 2.44, La〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 4.43, Ce〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 0.86, Pr〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 0.32, Nd〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 1.31, SiO〈sub〉2〈/sub〉 34.84, H〈sub〉2〈/sub〉O 2.9, total 100.10. The empirical formula based on 78 O atoms is [Ca〈sub〉16.48〈/sub〉(La〈sub〉0.84〈/sub〉Y〈sub〉0.67〈/sub〉Ce〈sub〉0.16〈/sub〉Nd〈sub〉0.24〈/sub〉Pr〈sub〉0.06〈/sub〉)Na〈sub〉0.47〈/sub〉]〈sub〉Σ18.92〈/sub〉(Al〈sub〉5.92〈/sub〉Mg〈sub〉4.22〈/sub〉Fe2.343+Mn0.553+)〈sub〉Σ13.03〈/sub〉Si〈sub〉17.95〈/sub〉O〈sub〉68.04〈/sub〉(OH)〈sub〉9.96〈/sub〉. The simplified formula is (Ca,〈span〉REE〈/span〉)〈sub〉19〈/sub〉Fe〈sup〉3+〈/sup〉Al〈sub〉4〈/sub〉(Mg,Al,Fe〈sup〉3+〈/sup〉)〈sub〉8〈/sub〉Si〈sub〉18〈/sub〉O〈sub〉68〈/sub〉(OH,O)〈sub〉10〈/sub〉. The crystal structure was refined to 〈span〉R〈/span〉 = 0.027 for 1684 unique observed reflections with |〈span〉F〈/span〉〈sub〉o〈/sub〉| ≥ 4σ〈sub〉F〈/sub〉. The mineral is tetragonal, 〈span〉P〈/span〉4/〈span〉nnc〈/span〉, 〈span〉a〈/span〉 = 15.6578(4), 〈span〉c〈/span〉 = 11.8597(5) Å, 〈span〉V〈/span〉 = 2907.6(2) Å〈sup〉3〈/sup〉, 〈span〉Z〈/span〉 = 2. Milanriederite is the analogue of vesuvianite with Mg predominant at the 〈span〉Y〈/span〉3 site. The strongest lines of the powder X-ray diffraction pattern are [〈span〉d〈/span〉, Å (〈span〉I〈/span〉, %) (〈span〉hkl〈/span〉)]: 2.970 (50) (511, 004), 2.774 (100) (204, 432, 440), 2.617 (87) (423, 531, 224, 522), 2.481 (30) (620), 2.143 (19) (315, 641), 1.676 (17) (921, 842, 436), 1.638 (38) (931, 526, 804, 922). The mineral is named in honour of Czech mineralogist Professor Milan Rieder (b. 1940), in recognition to his contributions to mineralogy and his service to the international mineralogical community.〈/span〉

Description: 〈span〉Rudabányaite was found in cavities of siliceous sphaerosiderite and limonite rocks at the Adolf mine area of the Rudabánya ore deposit (northern-East Hungary). The new mineral forms small crystals up to 0.6 mm and aggregates of a few mm across. Usually they have a xenomorphic shape, only occasionally cubic symmetry is morphologically discernible; the crystal forms {110} and {100} were recognized. The crystals are transparent, have yellowish-orange to brownish-yellow colour and a lemon-yellow streak, the lustre is adamantine. The Mohs’ hardness is 3–4. No cleavage was observed. Rudabányaite is optically isotropic. The density could not be measured due to lack of material; ρ(calc.) = 8.04 g/cm〈sup〉3〈/sup〉. Electron-microprobe analyses gave the average composition (in wt%) Ag〈sub〉2〈/sub〉O 29.39, Hg〈sub〉2〈/sub〉O 52.62, As〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 13.69, Cl 4.62, SO〈sub〉3〈/sub〉 0.19, O=Cl −1.04, sum 99.47. The empirical formula based on four oxygen atoms is (Ag〈sub〉2.06〈/sub〉Hg〈sub〉2.05〈/sub〉)〈sub〉Σ=4.11〈/sub〉(As〈sub〉0.97〈/sub〉S〈sub〉0.02〈/sub〉)〈sub〉Σ=0.99〈/sub〉O〈sub〉4〈/sub〉Cl〈sub〉1.06〈/sub〉; the idealized formula as derived from chemical analyses and crystal-structure investigation is [Ag〈sub〉2〈/sub〉Hg〈sub〉2〈/sub〉][AsO〈sub〉4〈/sub〉]Cl. The crystal-structure investigation was performed on single-crystal X-ray data; the refinements on 〈span〉F〈/span〉〈sup〉2〈/sup〉 converged at 〈span〉wR〈/span〉2(〈span〉F〈/span〉〈sup〉2〈/sup〉) = 0.068 and 〈span〉R〈/span〉1(〈span〉F〈/span〉) = 0.031 for all 972 unique data and 53 variable parameters. Rudabányaite crystallizes in space group F4¯3c, 〈span〉a〈/span〉 = 17.360(3) Å, 〈span〉V〈/span〉 = 5231.8 Å〈sup〉3〈/sup〉, 〈span〉Z〈/span〉 = 32. The crystal structure is characterised by two crystallographically different [〈span〉M〈/span〉〈sub〉4〈/sub〉]〈sup〉4+〈/sup〉 cluster cations forming tetrahedra; 〈span〉M〈/span〉 = (Ag,Hg) with a ratio Ag:Hg ~ 1:1. There is not any evidence for an order between the Ag and Hg atoms. Small amounts of the 〈span〉M〈/span〉 atoms are displaced by ~0.5 Å. Topologically, the barycentres of the [〈span〉M〈/span〉〈sub〉4〈/sub〉]〈sup〉4+〈/sup〉 clusters and the As atom positions of the crystal structure of rudabányaite form a cubic primitive lattice with 〈span〉a〈/span〉′ = ½〈span〉a〈/span〉 = 8.68 Å; half of the voids are occupied by Cl atoms.〈/span〉

Description: 〈span〉Hjalmarite, ideally 〈sup〉A〈/sup〉Na〈sup〉B〈/sup〉(NaMn)〈sup〉C〈/sup〉Mg〈sub〉5〈/sub〉〈sup〉T〈/sup〉Si〈sub〉8〈/sub〉O〈sub〉22〈/sub〉〈sup〉W〈/sup〉(OH)〈sub〉2〈/sub〉, is a new root-name member of the amphibole supergroup, discovered in skarn from the Långban Fe–Mn–(Ba–As–Pb–Sb–Be–B) deposit, Filipstad, Värmland, Sweden (IMA-CNMNC 2017-070). It occurs closely associated with mainly rhodonite and quartz. It is grayish white with vitreous luster and non-fluorescent. The crystals are up to 5 mm in length and display splintery fracture and perfect cleavage on {110}. Hjalmarite is colorless (non-pleochroic) in thin section and optically biaxial (–), with α = 1.620(5), β = 1.630(5), γ = 1.640(5). The calculated density is 3.12 Mg/m〈sup〉3〈/sup〉. Average VHN〈sub〉100〈/sub〉 is 782, corresponding to 〈span〉ca.〈/span〉 5½ Mohs. An empirical formula, derived from electron-microprobe analyses in combination with crystal-structure refinements, is (Na〈sub〉0.84〈/sub〉K〈sub〉0.16〈/sub〉)〈sub〉Σ1〈/sub〉(Na〈sub〉1.01〈/sub〉Mn〈sub〉0.55〈/sub〉Ca〈sub〉0.43〈/sub〉Sr〈sub〉0.01〈/sub〉)〈sub〉Σ2〈/sub〉(Mg〈sub〉3.83〈/sub〉Mn〈sub〉1.16〈/sub〉Al〈sub〉0.01〈/sub〉)〈sub〉Σ5〈/sub〉(Si〈sub〉7.99〈/sub〉Al〈sub〉0.01〈/sub〉)〈sub〉Σ8〈/sub〉O〈sub〉22〈/sub〉(OH〈sub〉1.92〈/sub〉F〈sub〉0.08〈/sub〉)〈sub〉Σ2.〈/sub〉 An infra-red spectrum of hjalmarite shows distinct absorption bands at 3673 cm〈sup〉−1〈/sup〉 and 3731 cm〈sup〉−1〈/sup〉 polarized in the α direction. The eight strongest Bragg peaks in the powder X-ray diffraction pattern are [〈span〉d〈/span〉 (Å), 〈span〉I〈/span〉 (%), (〈span〉hkl〈/span〉)]: 3.164, 100, (310); 2.837, 50, (330); 8.50, 44, (110); 3.302; 40, (240); 1.670, 34, (461); 1.448, 32, (6¯61); 2.727, 30, (151); 2.183, 18 (261). Single-crystal X-ray diffraction data were collected at 298 K and 180 K. The crystal structure at ambient temperature was refined in space group 〈span〉C〈/span〉2/〈span〉m〈/span〉 to 〈span〉R〈/span〉1 = 2.6% [〈span〉I〈/span〉 〉 2σ(〈span〉I〈/span〉)], with observed unit-cell parameters 〈span〉a〈/span〉 = 9.9113(3), 〈span〉b〈/span〉 = 18.1361(4), 〈span〉c〈/span〉 = 5.2831(5) Å, β = 103.658(5)° and 〈span〉V〈/span〉 = 922.80(9) Å〈sup〉3〈/sup〉. The 〈span〉A〈/span〉 and 〈span〉M〈/span〉(4) sites split into 〈span〉A〈/span〉(〈span〉m〈/span〉) (K〈sup〉+〈/sup〉, Na〈sup〉+〈/sup〉), 〈span〉A〈/span〉(2) (Na〈sup〉+〈/sup〉), and 〈span〉M〈/span〉(4’) (Mn〈sup〉2+〈/sup〉) subsites, respectively. Among the octahedrally coordinated C group cations, Mn〈sup〉2+〈/sup〉 orders strongly at the 〈span〉M〈/span〉(2) site. No significant violation of 〈span〉C〈/span〉2/〈span〉m〈/span〉 symmetry or change in the structure topology was detected at low temperature (〈span〉R〈/span〉1 = 2.1%). The hjalmarite-bearing skarn formed at peak regional metamorphism, 〈span〉T〈/span〉 ≥ 600 °C, at conditions of high SiO〈sub〉2〈/sub〉 activity and relatively low oxygen fugacity. The mineral name honors the Swedish geologist and mineralogist S.A. Hjalmar Sjögren (1856–1922).〈/span〉

Description: 〈span〉Miarolitic pockets from the 1628 Ma Luumäki pegmatite in SE Finland contain gem-quality beryl (heliodor) within a matrix of reddish hematite, biotite, muscovite, chlorite, quartz, kaolinite, and bertrandite. Two different types of gem-beryl-bearing miarolitic pockets were observed, one in the intermediate zone of the pegmatite close to the contact with the quartz core, and the other at the border of the pegmatite body, at the contact with the host-rock rapakivi granite. Although similar in appearance, the pockets were formed by two distinct processes, as demonstrated by their structural position and the trace element chemistry of beryl. The stage-I gem beryls formed in miarolitic pockets in the intermediate zone, when the last batches of highly fractionated melt strongly enriched in incompatible and fluxing elements and volatiles crystallized. This is demonstrated by the trace element composition of gem beryls (Sc, Fe, Ga and Cs contents), which are aligned on a trend with magmatic common beryls, which had crystallized earlier in the inner intermediate zone. Subsequently, the later, stage-II gem beryls formed in miarolitic pockets at the border of the pegmatite from a hydrothermal fluid that escaped from the inner part of the pegmatite. This is demonstrated by the distinct trace element composition of these gem beryls, notably the high Li and Na concentrations, the abundance of fluid inclusions, and the textural association with a particular type of K-feldspar, which is chemically distinct from the magmatic fractionation trend connecting all other magmatic K-feldspars of the Luumäki pegmatite. The hydrothermal fluid caused local alteration of some of the magmatic common beryl crystals, resulting in changes in their trace element composition, as well as alteration of the host-rock rapakivi granites. The two distinct stages of gem-beryl formation in the Luumäki pegmatite, therefore, record the transition from a silicate melt-dominated to a fluid-dominated system.〈/span〉

Description: 〈span〉Ecdemite from Harstigen, Värmland, Central Sweden, was studied through Raman and FTIR spectroscopy, electron-microprobe techniques, synchrotron powder and single-crystal diffraction. The ideal mineral formula proposed by Palache, Pb〈sub〉6〈/sub〉Cl〈sub〉4〈/sub〉As〈sub〉2〈/sub〉O〈sub〉7〈/sub〉, is confirmed. In contrast to previous suggestions, however, the present study demonstrates that the mineral is monoclinic, with space-group type 〈span〉P〈/span〉2〈sub〉1〈/sub〉 and unit-cell parameters 〈span〉a〈/span〉 = 10.828(4) Å, 〈span〉b〈/span〉 = 10.826(2) Å, 〈span〉c〈/span〉 = 6.970(1) Å, β = 113.26°(2). The crystal-structural study of ecdemite shows that the mineral can be considered as made up of regularly alternating Cl layers and litharge-like defective layers, also hosting As cations, with the representative formula {Pb〈sub〉2〈/sub〉[Pb〈sub〉4〈/sub〉O](AsO〈sub〉3〈/sub〉)〈sub〉2〈/sub〉}〈sup〉4+〈/sup〉, in a 1:1 ratio. These features indicate that ecdemite can be considered as a new member of the layered lead oxyhalides group.〈/span〉

Description: 〈span〉Ferrirockbridgeite, ideally (Fe0.673+□〈sub〉0.33〈/sub〉)〈sub〉2〈/sub〉(Fe〈sup〉3+〈/sup〉)〈sub〉3〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉3〈/sub〉(OH)〈sub〉4〈/sub〉(H〈sub〉2〈/sub〉O), is a new member of the rockbridgeite group. The type specimen is from the Palermo No. 1 pegmatite in North Groton, Grafton County, New Hampshire, USA. Electron microprobe analysis, coupled with Mössbauer spectroscopy for FeO and thermogravimetric analysis (TGA) for H〈sub〉2〈/sub〉O gives the empirical formula Mn0.312+Fe0.082+Mg0.01Zn0.03Ca0.05Fe4.183+P2.87O17H6.11. Ferrirockbridgeite is orthorhombic, space group 〈span〉Bbmm〈/span〉 with 〈span〉a〈/span〉 = 13.853(1), 〈span〉b〈/span〉 = 16.928(1), 〈span〉c〈/span〉 = 5.1917(5) Å and 〈span〉Z〈/span〉 = 4. Optically, ferrirockbridgeite is biaxial (–), with α = 1.875(5), β = 1.890(calc), γ = 1.900(5) (measured in white light) and 2〈span〉V〈/span〉 (meas) is 78(1)° from extinction data. The dispersion is strong, with 〈span〉r〈/span〉 〉 〈span〉v〈/span〉. The optical orientation is 〈span〉X〈/span〉 = 〈strong〉c〈/strong〉, 〈span〉Y〈/span〉 = 〈strong〉a〈/strong〉, 〈span〉Z〈/span〉 = 〈strong〉b〈/strong〉. The pleochroism is 〈span〉X〈/span〉 = yellow brown, 〈span〉Y〈/span〉 = olive brown, 〈span〉Z〈/span〉 = dark olive green; 〈span〉Z〈/span〉 〉 〈span〉Y〈/span〉 〉 〈span〉X〈/span〉. Crystal structure refinements on ferrirockbridgeite and other oxidized rockbridgeite-group species, including type rockbridgeite and type frondelite, show that oxidation is accompanied by loss of Fe〈sup〉2+〈/sup〉 from the 〈span〉M〈/span〉2 site according to the reaction [3Fe〈sup〉2+〈/sup〉] → [2Fe〈sup〉3+〈/sup〉 + □] + Fe〈sup〉2+〈/sup〉(removed) +2e〈sup〉−〈/sup〉. A variable portion of the Fe removed from the 〈span〉M〈/span〉2 site becomes trapped at 〈span〉M〈/span〉3 site vacancies. A general formula for oxidized rockbridgeite-group minerals is presented.〈/span〉