ALBERT

Description: Colourless crystals of the novel compound BaYb 6 (Si 2 O 7 ) 2 (Si 3 O 10 ) were prepared using a high-temperature flux-growth technique in air. The crystal structure was solved and refined to R ( F ) = 2.50 % using single-crystal X-ray diffraction data collected at room temperature. The silicate is monoclinic, space group P 2 1 / m ( Z = 2), with a = 5.5173(11), b = 27.260(6), c = 6.8150(14) Å, β = 106.73(3)°, V = 981.6(3) Å 3 . BaYb 6 (Si 2 O 7 ) 2 (Si 3 O 10 ) represents the first silicate containing both (Si 2 O 7 ) and (Si 3 O 10 ) groups in the ratio 2:1 and is isotypic with (NH 4 )Cd 6 (P 2 O 7 ) 2 (P 3 O 10 ). Its framework topology is characterised by one horseshoe-shaped trisilicate (Si 3 O 10 ) group, two symmetrically equivalent (Si 2 O 7 ) groups with the Si–O–Si angle of 165.3° and staggered conformation, and zigzag chains of edge-sharing distorted YbO 6 octahedra (〈Yb–O = 2.24 Å〉). The Ba atoms occupy narrow channels extending parallel to [100]. The topological features of BaYb 6 (Si 2 O 7 ) 2 (Si 3 O 10 ) are compared to those of other compounds containing mixed groups ( M 2 O 7 ) and ( M 3 O 10 ). A similarity to BaY 4 (Si 2 O 7 )(Si 3 O 10 ) is pointed out.

Description: New data for parnauite from the type locality, Majuba Hill, Nevada, USA (MH; type specimen), and also from Cap Garonne, Var, France (CG), and the Clara Mine, Baden-Württemberg, Germany, are presented. The average chemical composition of MH material is (Cu 8.82 Al 0.16 Fe 0.02 ) 9.00 (As 1.78 Al 0.07 Si 0.08 S 0.07 ) 2.00 O 8 (SO 4 )(OH) 10 ·7H 2 O and that of CG parnauite, (Cu 8.42 Al 0.21 Zn 0.10 ) 8.73 (AsO 4 ) 2 [(S 0.97 As 0.10 ) 1.07 O 4 ](OH 9.23 Cl 0.77 ) 10.00 · 7H 2 O. Both of these formulae confirm the 9:2:1 Cu:As:S ratio obtained from earlier descriptions of parnauite. Raman spectra for parnauite from both localities are very similar. Bands are assigned, but show no evidence of the presence of CO 3 , in contrast to previous studies, and no distinct Cu–Cl stretching mode. It appears that neither the minor CO 3 and PO 4 previously reported nor Cl are essential constituents of parnauite. Single-crystal XRD analysis indicates a primitive orthorhombic unit cell with dimensions 6 x 14 x 15 Å, similar to previous studies, but h = odd reflections were heavily streaked and diffuse, preventing full refinement. A 3 Å substructure was refined, with space group Pmn 2 1 , to R 1 ( F ) = 0.0750 (MH). For a MH crystal, the subcell had a = 3.0113(4), b = 14.259(3), c = 14.932(2) Å, V = 641.13(16) Å 3 and Z = 1. The structure is of a new type, and contains Cu in 6 distinct sites, forming two three-polyhedron wide ribbons of edge-sharing Cu-O polyhedra extended parallel to the a - axis. The two ribbons lie back-to-back and are bridged by two AsO 4 tetrahedra. The collection of 6Cu + 2As cations plus ligands forms a rod-like moiety extended || a . These rods link through polyhedral corners to form complex, corrugated (010) layers. The interlayer space is occupied by H 2 O molecules. Thus, the disorder observed by XRD is of an unusual type, in which the shape of the unit mesh within layers is variable, rather than the stacking of the layers. Disorder arises because each AsO 4 tetrahedron shares a face with a Cu(O,OH,H 2 O) 5–6 polyhedron in the substructure, necessitating partial occupancy of both As and Cu sites. The S atoms were not located in the refinement, but four electron-density maxima in the interlayer region were interpreted as H 2 O molecules. Hence, the simplified structural formula derived from the substructure is (Cu 10 2 )(As 2 2 )O 8 (OH) 14 ·8H 2 O, deviating from that obtained in chemical analyses. The discrepancy presumably arises due to strong delocalisation of the sulphur and the apical oxygen of the SO 4 tetrahedron in the substructure. Short-range order of Cu–As and Cu–S || a can occur independently in the relevant structural rods, which accounts for the observed long-range disorder. Cell parameters and substructures obtained from CG and Clara material are similar to those from the MH crystal. Site splitting of OH positions in the CG refinement indicates that Cl is distributed over several sites in the 3 Å substructure, making the mineral a Cl-rich variety of parnauite rather than a distinct mineral species.

Description: 〈span〉Lavinskyite-1〈span〉M〈/span〉, a monoclinic MDO (Maximum Degree of Order) polytype related to the orthorhombic MDO polytype lavinskyite-2〈span〉O〈/span〉 (formerly lavinskyite, now redefined), was identified in samples from the Cerchiara manganese mine (Liguria, Italy). Both polytypes have the same ideal chemical formula, K(LiCu)Cu〈sub〉6〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉11〈/sub〉)〈sub〉2〈/sub〉(OH)〈sub〉4〈/sub〉. Lavinskyite-1〈span〉M〈/span〉 was originally approved as “liguriaite”, but was subsequently redefined as lavinskyite-1〈span〉M〈/span〉 (IMA proposal 16-E).Lavinskyite-1〈span〉M〈/span〉 occurs as blue, micaceous aggregates embedded in calcite-filled microfractures and veinlets, where it is associated with calcite, quartz, norrishite and “schefferite” (a Mn-bearing variety of diopside). Lavinskyite-1〈span〉M〈/span〉 is translucent to transparent, bluish to pale blue in colour with a very pale blue to whitish streak and vitreous lustre; it is non-fluorescent. Individual, always indistinct platelets are up to ∼0.15 mm in length. The crystals are tabular (100) and elongate along [001]. Lavinskyite-1〈span〉M〈/span〉 is brittle with perfect cleavage parallel to {100}, and uneven fracture. The estimated Mohs hardness is ∼5. The calculated density is 3.613 g/cm〈sup〉3〈/sup〉 (for empirical formula). Optically, it is biaxial positive, with α = 1.674(2); β = 1.692(3) and γ = 1.730(3); 2〈span〉V〈/span〉〈sub〉γ〈/sub〉 is very large, ∼75° (est.), 2〈span〉V〈/span〉〈sub〉γ〈/sub〉 (calc.) = 70°. Pleochroism is moderate: 〈span〉X〈/span〉 (pale) blue, 〈span〉Y〈/span〉 pale blue and 〈span〉Z〈/span〉 pale blue with faint greenish tint; absorption 〈span〉X〈/span〉 ≥ 〈span〉Z〈/span〉 ≥ 〈span〉Y〈/span〉. Orientation: 〈span〉X〈/span〉 ^ 〈span〉a〈/span〉 ∼20° (probably in obtuse beta), 〈span〉Y〈/span〉 = 〈span〉b〈/span〉, 〈span〉Z〈/span〉 ∼ 〈span〉c〈/span〉; optical elongation is positive and the optical axis plane is parallel to (010). No dispersion was observed.Chemical analysis (quantitative SEM-EDS and LAICPMS) of two samples yielded the empirical formulae (based on 26 O atoms) (K〈sub〉1.08〈/sub〉)〈sub〉Σ1.08〈/sub〉(Li〈sub〉0.89〈/sub〉Mg〈sub〉0.36〈/sub〉Cu〈sub〉0.33〈/sub〉Na〈sub〉0.22〈/sub〉Mn〈sup〉2+〈/sup〉〈sub〉0.04〈/sub〉)〈sub〉Σ1.86­〈/sub〉Cu〈sub〉6.00〈/sub〉Si〈sub〉8.08〈/sub〉O〈sub〉22〈/sub〉(OH)〈sub〉4〈/sub〉 and (K〈sub〉1.08〈/sub〉)〈sub〉Σ1.08〈/sub〉(Li〈sub〉0.89〈/sub〉Cu〈sub〉0.35〈/sub〉Mg〈sub〉0.28〈/sub〉Na〈sub〉0.22〈/sub〉Mn〈sup〉2+〈/sup〉〈sub〉0.04〈/sub〉) 〈sub〉Σ1.78­〈/sub〉Cu〈sub〉6.00〈/sub〉Si〈sub〉8.12〈/sub〉O〈sub〉22〈/sub〉(OH)〈sub〉4〈/sub〉. Strongest lines in the X-ray powder diffraction pattern are [〈span〉d〈/span〉 in Å (〈span〉I〈/span〉〈sub〉calc〈/sub〉) 〈span〉hkl〈/span〉]): 10.216 (100) 100, 9.007 (20) 110, 4.934 (19) 210, 3.983 (19) 230, 3.353 (33) 310, 2.8693 (22) 241, 2.6155 (35) 161, 2.3719 (23) 20-2. The crystal structure has been solved, using single-crystal X-ray diffractometer data (〈span〉Rint〈/span〉 = 4.60%), by direct methods and refined in space group 〈span〉P〈/span〉2〈sub〉1〈/sub〉/〈span〉c〈/span〉 (no. 14) to 〈span〉R〈/span〉1 = 5.10% and 〈span〉wR〈/span〉2〈sub〉〈span〉all〈/span〉〈/sub〉 = 13.92% [1786 ‘observed’ reflections with 〈span〉F〈/span〉〈sub〉o〈/sub〉 〉 4σ(〈span〉F〈/span〉〈sub〉o〈/sub〉), 199 parameters]. Refined unit-cell parameters are: 〈span〉a〈/span〉 = 10.224(2), 〈span〉b〈/span〉 = 19.085(4), 〈span〉c〈/span〉 = 5.252(1) Å, β = 92.23(3)°, 〈span〉V〈/span〉 = 1024.0(4) Å〈sup〉3〈/sup〉 (〈span〉Z〈/span〉 = 2). The chemical composition and crystal structure are supported by micro-Raman spectra.Lavinskyite-1〈span〉M〈/span〉 has a sheet structure consisting of corrugated brucite-like (CuO〈sub〉2〈/sub〉)〈sub〉n〈/sub〉 layers with amphibole-type (SiO〈sub〉3〈/sub〉)〈sub〉n〈/sub〉 chains joined to both their upper and lower surfaces. Adjacent complex sheets are linked by [5]-coordinated Li atoms and Cu atoms in square coordination (nearly planar) and interlayer K atoms. Lavinskyite-1〈span〉M〈/span〉 is isostructural with a hypothetical monoclinic MDO polytype of plancheite, not yet found in nature, while lavinskyite-2〈span〉O〈/span〉 is isostructural with plancheite. It appears that a complex and delicate interplay between the Li:Cu and Cu:Mg ratios (lower in lavinskyite-1〈span〉M〈/span〉), along with an additional influence of impurity cations such as Na and different conditions of formation, results in a stabilisation of the 1〈span〉M〈/span〉 polytype. The origin of lavinskyite-1〈span〉M〈/span〉 can be related to a complex, multi-stage hydrothermal evolution of the primary Fe-Mn ore at Cerchiara, which experienced a diffuse alkali metasomatism under strongly oxidising conditions and produced mineral assemblages enriched in Na, K and Li, while providing also appreciable amounts of Ba, Sr, Ca and Cu.〈/span〉

Description: 〈span〉Vanderheydenite, Zn〈sub〉6〈/sub〉(PO〈sub〉4〈/sub〉)〈sub〉2〈/sub〉(SO〈sub〉4〈/sub〉)(OH)〈sub〉4〈/sub〉·7H〈sub〉2〈/sub〉O, is a new mineral from the Block 14 Opencut, Broken Hill, New South Wales, Australia. It occurs as aggregates of colourless crystals up to 0.5 mm across in voids of a sphalerite–galena matrix and is associated with anglesite, pyromorphite, sulfur, and liversidgeite. Crystals are pseudohexagonal blades up to 0.4 mm in length, flattened on {1 0 0} and exhibiting the forms {1 0 0}, {0 1 0}, and {0 2 1}. Cleavage was not observed. The Mohs hardness is estimated to be 3. The calculated density is 3.12 g/cm〈sup〉3〈/sup〉 from the empirical formula and 3.06 g/cm〈sup〉3〈/sup〉 from the ideal formula. The mineral is optically biaxial (–), with α = 1.565(4), β = 1.580(4) and γ = 1.582(4). The calculated 2〈span〉V〈/span〉 is 39.8°. Chemical analysis by electron microprobe gave ZnO 55.63, CuO 0.07, FeO 0.11, MnO 0.06, P〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 14.18, As〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 4.33, SO〈sub〉3〈/sub〉 8.71, H〈sub〉2〈/sub〉O 18.31, total 101.40 wt%, with H〈sub〉2〈/sub〉O content derived from the refined crystal structure. The empirical formula calculated on the basis of 23 oxygen atoms is (Zn〈sub〉5.99〈/sub〉Cu〈sub〉0.01〈/sub〉Fe〈sub〉0.01〈/sub〉Mn〈sub〉0.01〈/sub〉)〈sub〉Σ6.02〈/sub〉[(PO〈sub〉4〈/sub〉)〈sub〉1.75〈/sub〉(AsO〈sub〉4〈/sub〉)〈sub〉0.33〈/sub〉]〈sub〉Σ2.08〈/sub〉(SO〈sub〉4〈/sub〉)〈sub〉0.95〈/sub〉(OH)〈sub〉3.91〈/sub〉·6.96H〈sub〉2〈/sub〉O. The mineral is monoclinic, 〈span〉P〈/span〉2〈sub〉1〈/sub〉/〈span〉n〈/span〉, with 〈span〉a〈/span〉 = 6.2040(12), 〈span〉b〈/span〉 = 19.619(4), 〈span〉c〈/span〉 = 7.7821(16) Å, β = 90.67(3)°, 〈span〉V〈/span〉 = 947.1(3) Å〈sup〉3〈/sup〉. The five strongest lines in the X-ray powder diffraction pattern are [〈span〉d〈/span〉(Å), (〈span〉I〈/span〉), (〈span〉hkl〈/span〉)]: 9.826 (57) (0 2 0), 7.296 (20) (0 1 1), 6.134 (1 0 0) (0 2 1), 3.368 (10) (0 3 2, 1 5 0), 3.069 (9) (2 1 0, 0 4 2). The crystal structure of vanderheydenite (〈span〉R〈/span〉1 = 0.0497 for 939 reflections with 〈span〉F〈/span〉〈sub〉o 〈/sub〉〉 4σ〈span〉F〈/span〉) contains chains of edge-sharing ZnO〈sub〉6〈/sub〉 octahedra parallel to 〈span〉a〈/span〉 that are linked by edge- and corner-sharing ZnO〈sub〉5〈/sub〉 trigonal bipyramids and 〈span〉T〈/span〉O〈sub〉4〈/sub〉 (〈span〉T〈/span〉 = P, As) tetrahedra forming zig-zag sheets parallel to {0 1 0}. Sheets are linked by half-occupied, distorted 〈span〉T〈/span〉O〈sub〉4〈/sub〉 (〈span〉T〈/span〉 = P, S) tetrahedra in the [0 1 1] direction. Interstitial channels extend parallel to the 〈span〉a〈/span〉-direction and are occupied by strongly to weakly hydrogen-bonded H〈sub〉2〈/sub〉O groups.〈/span〉

Description: Fluor-schorl, NaFe 2+ 3 Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 3 F, is a new mineral species of the tourmaline supergroup from alluvial tin deposits near Steinberg, Zschorlau, Erzgebirge (Saxonian Ore Mountains), Saxony, Germany, and from pegmatites near Grasstein (area from Mittewald to Sachsenklemme), Trentino, South Tyrol, Italy. Fluor-schorl was formed as a pneumatolytic phase and in high-temperature hydrothermal veins in granitic pegmatites. Crystals are black (pale brownish to pale greyish-bluish, if 〈0.3 mm in diameter) with a bluish-white streak. Fluor-schorl is brittle and has a Mohs hardness of 7; it is non-fluorescent, has no observable parting and a poor/indistinct cleavage parallel to {0001}. It has a calculated density of ~3.23 g/cm 3 . In plane-polarized light, it is pleochroic, O = brown to grey-brown (Zschorlau), blue (Grasstein), E = pale grey-brown (Zschorlau), cream (Grasstein). Fluor-schorl is uniaxial negative, = 1.660(2)–1.661(2), = 1.636(2)–1.637(2). The mineral is rhombohedral, space group R 3 m, a = 16.005(2), c = 7.176(1) Å, V = 1591.9(4) Å 3 (Zschorlau), a = 15.995(1), c = 7.166(1) Å, V = 1587.7(9) Å 3 (Grasstein), Z = 3. The eight strongest observed X-ray diffraction lines in the powder pattern [ d in Å ( I ) hkl ] are: 2.584(100)(051), 3.469(99)(012), 2.959(83)(122), 2.044(80)(152), 4.234(40)(211), 4.005(39)(220), 6.382(37)(101), 1.454(36)(514) (Grasstein). Analyses by a combination of electron microprobe, secondary-ion mass spectrometry (SIMS), Mössbauer spectroscopic data and crystal-structure refinement result in the structural formulae X (Na 0.82 K 0.01 Ca 0.01 0.16 ) Y (Fe 2+ 2.30 Al 0.38 Mg 0.23 Li 0.03 Mn 2+ 0.02 Zn 0.01 0.03 ) 3.00 Z (Al 5.80 Fe 3+ 0.10 Ti 4+ 0.10 ) T (Si 5.81 Al 0.19 O 18 ) (BO 3 ) 3 V (OH) 3 W [F 0.66 (OH) 0.34 ] (Zschorlau) and X (Na 0.78 K 0.01 0.21 ) Y (Fe 2+ 1.89 Al 0.58 Fe 3+ 0.13 Mn 3+ 0.13 Ti 4+ 0.02 Mg 0.02 Zn 0.02 0.21 ) 3.00 Z (Al 5.74 Fe 3+ 0.26 ) T (Si 5.90 Al 0.10 O 18 ) (BO 3 ) 3 V (OH) 3 W [F 0.76 (OH) 0.24 ] (Grasstein). Several additional, newly confirmed occurrences of fluor-schorl are reported. Fluor-schorl, ideally NaFe 2+ 3 Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 3 F, is related to end-member schorl by the substution F -〉 (OH). The chemical compositions and refined crystal structures of several schorl samples from cotype localities for schorl (alluvial tin deposits and tin mines in the Erzgebirge, including Zschorlau) are also reported. The unit-cell parameters of schorl from these localities are slightly variable, a = 15.98–15.99, c = 7.15–7.16 Å, corresponding to structural formulae ranging from ~ X (Na 0.5 0.5 ) Y (Fe 2+ 1.8 Al 0.9 Mg 0.2 0.1 ) Z (Al 5.8 Fe 3+ 0.1 Ti 4+ 0.1 ) T (Si 5.7 Al 0.3 O 18 ) (BO 3 ) 3 V (OH) 3 W [(OH) 0.9 F 0.1 ] to ~ X (Na 0.7 0.3 ) Y (Fe 2+ 2.1 Al 0.7 Mg 0.1 0.1 ) Z (Al 5.9 Fe 3+ 0.1 ) T (Si 5.8 Al 0.2 O 18 ) (BO 3 ) 3 V (OH) 3 W [(OH) 0.6 F 0.4 ]. The investigated tourmalines from the Erzgebirge show that there exists a complete fluor-schorl–schorl solid-solution series. For all studied tourmaline samples, a distinct inverse correlation was observed between the X –O2 distance (which reflects the mean ionic radius of the X -site occupants) and the F content ( r 2 = 0.92). A strong positive correlation was found to exist between the F content and the 〈 Y –O〉 distance ( r 2 = 0.93). This correlation indicates that Fe 2+ -rich tourmalines from the investigated localities clearly tend to have a F-rich or F-dominant composition. A further strong positive correlation ( r 2 = 0.82) exists between the refined F content and the Y–W (F,OH) distance, and the latter may be used to quickly estimate the F content.