ALBERT

Description: A bstract This work presents the results of investigation of the primary minerals and their weathering products of two tailing ponds near the villages of Rudňany and Slovinky in eastern Slovakia. The tailings are near-neutral or slightly alkaline (pH = 7.2–8.8) because the acidity generated by the decomposition of the sulfides is efficiently neutralized by the abundant carbonate minerals. The most frequent primary gangue minerals are siderite, quartz, barite, and muscovite. The prevailing primary sulfide minerals in both tailing ponds are pyrite and chalcopyrite; less common are tetrahedrite and arsenopyrite. The most frequent secondary and tertiary ( i.e. , formed in the tailings, not in the oxidation zone of the deposits) minerals at both localities are iron oxides, either goethite or poorly crystalline hydrous ferric oxide. Other minerals (cuprite, malachite, delafossite; identified by X-ray microdiffraction or Raman spectroscopy) are minor or rare and occur only in Slovinky. The iron oxide minerals are enriched in a suite of elements, including Cu, Si, Ca, Zn, As, Mg, and Mn. The transformations of the poorly crystalline hydrous ferric oxide to goethite and maturation of goethite is controlled by both high-valence tetrahedral cations (Si, As, P) and lower-valence octahedral cations (Cu), as shown by the measurements of the size of coherently diffracting domains in goethite and the chemical composition of goethite. The iron oxide minerals, by virtue of their adsorption capacity, prevent separate minerals of many metals and metalloids (Cu, Ca, As, Sb) from nucleating and growing, and therefore control the entire neutral mine drainage (NMD) system. Geochemical modeling of the discharged waters shows that all common Cu and ferric arsenate minerals are strongly undersaturated, confirming the central role of iron oxide phases in the NMD system.

Description: Distinctly chemically zoned tourmaline was found in a quartz vein near Tisovec, Slovak Ore Mountains, Slovakia. The tourmaline forms radial aggregates of light grey to green thin prismatic to acicular crystals growing in cracks in the host rock. The root zone of the aggregates has dravitic to oxy-dravitic compositions, shifting to magnesio-foitite in the middle parts of the crystals and to foititic compositions in the outer parts of the aggregates. The optimized formula, considering the single-crystal structure refinement (SREF) and the chemistry of the magnesio-foititic zone, is ~ X ( 0.5 Na 0.4 Ca 0.1 ) Y (Mg 1.1 Al 1.0 Fe 2+ 0.8 Fe 3+ 0.1 ) Z (Al 5.7 Fe 3+ 0.3 ) (Si 5.9 Al 0.1 O 18 ) (BO 3 ) 3 (OH) 3 [O 0.6 (OH) 0.3 F 0.1 ], with lattice parameters (SREF) a 15.929(2) Å, c 7.163(1) Å, and V 1574.0(7) Å 3 . SREF data as well as a detailed study of bond lengths indicate a dominancy of Al 3+ at the Z site substituted by a small proportion of Fe 3+ , while Fe 2+ and Mg 2+ essentially occupy the Y site along with a significant amount of Al. The chemical composition is controlled by the substitutions FeMg –1 , Al(Fe,Mg) –1 Na –1 , and AlO(Fe,Mg) –1 (OH) –1 . The AlO(Fe,Mg) –1 (OH) –1 substitution is dominant in the transition from oxy-dravite to magnesio-foitite, and the Al(Fe,Mg) –1 Na –1 substitution prevails in the magnesio-foitite and foitite compositions. Both proton- and alkali-deficient substitutions produce the enrichment in Al which can be linked to the forming of the acicular habit. Aluminum strongly prefers the Z -site, whose octahedra form a network of chains parallel to c . Consequently, polymerization of the Z O 6 octahedral network will dominate growth in the a direction. Therefore, the chemical composition, mainly Al enrichment, which is common for most of the acicular to fibrous tourmalines, can be an important factor promoting preferential growth in the c direction. The rate and time for crystallization, which depend mostly on the temperature and cooling rate, are also factors which should be considered.

Description: Tourmalines with Al 3+ , Mg 2+ , Fe 3+ , Fe 2+ , Mn 2+ , V 3+ , and Cr 3+ cation disorder at the two octahedrally coordinated sites ( Y , Z ) have recently been described. Their complete structural and compositional description enabled a detailed statistical study of Mg 2+ , Al 3+ , and Fe 2+ disorder reactions. The sizes of the a and c unit-cell parameters are positively correlated with 〈 Y –O〉 and 〈 Z –O〉 bond lengths, respectively, and this enables inference of octahedral distortion. While total octahedral Al 3+ and Mg 2+ show weak negative correlations with a consistent with their relatively smaller ionic radii, Fe 2+ has a weak positive correlation with a because of its larger ionic radius. Negative Al 3+ and positive Mg 2+ correlations with c show that increased Mg 2+ content, rather than Al 3+ , is related to increased c and Z O 6 octahedral dilation. Fe 2+ negatively correlates with c , and this suggests that none or only a negligible Fe 2+ proportion can be incorporated at the Z site. All Y -site bond lengths except Y –O2 increase with the occupancy of Fe 2+ at the Y site and decrease with the occupancy of Mg at the Y site. Al 3+ has no significant effect except for Y –O2 bond-length contraction. In contrast, Al 3+ negatively correlates with all bonds involving the Z site, and Mg 2+ has the opposite effect. Fe 2+ shows negative correlation with Z –O bond lengths, which also suggests that Fe 2+ is not present at the Z site in any significant amount. Consequently, although Al-Mg disorder may be very common in Mg-bearing tourmalines but should never be over 2 apfu Mg at the Z site, disorder involving Z Fe 2+ seems unlikely. Complementary bond-topology graphs revealed that Z R 2+ induces increased bond valence and decreased Y –O6 bond length, with consequent Y –O2 bond-valence decrease and bond-length increase. This corresponds with variations in bond lengths dependent on site occupancy, especially since Y R 2+ requires the presence of R 3+ at neighboring Y sites. A topological study of selected structural arrangements reveals that Y R 2+ – Z R 3+ – Z R 3+ and Y R 3+ – Z R 3+ – Z R 2+ arrangements with W OH can exist together in bond-valence stability. In contrast, bond-valence requirements involving W O have more degrees of freedom. Consequently, although these bond-valence requirements may produce structures with Al-Mg disorder, the disorder most likely occurs in arrangements with W OH.

Description: Oxy-schorl (IMA 2011-011), ideally Na(Fe 2+ 2 Al)Al 6 Si 6 O1 8 (BO 3 ) 3 (OH) 3 O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Pribyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm 3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm 3 (Pribyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Pribyslavice), uniaxial negative, = 1.663(2), = 1.641(2) (Zlatá Idka) and = 1.662(2), = 1.637(2) (Pribyslavice). Oxy-schorl is trigonal, space group R 3 m , Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å 3 (Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å 3 (Pribyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Pribyslavice) is (in wt%): SiO 2 33.85 (34.57), TiO 2 〈0.05 (0.72), Al 2 O 3 39.08 (33.55), Fe 2 O 3 not determined (0.61), FeO 11.59 (13.07), MnO 〈0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na 2 O 1.67 (1.76), K 2 O 〈0.02 (0.03), F 0.26 (0.56), Cl 0.01 (〈0.01), B 2 O 3 (calc.) 10.39 (10.11), H 2 O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Pribyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na 0.591 Ca 0.103 0.306 ) 1.000 (Al 1.885 Fe 2+ 1.108 Mn 0.005 Ti 0.002 ) 3.000 (Al 5.428 Mg 0.572 ) 6.000 (Si 5.506 Al 0.494 ) 6.000 O 18 (BO 3 ) 3 (OH) 3 (O 0.625 OH 0236 F 0.136 Cl 0.003 ) 1000 for Zlatá Idka, and (Na 0.586 Ca 0.017 K 0.0060.391 ) 1.000 (Fe 2+ 1.879 Mn 0.015 Al 1.013 Ti 0.093 ) 3.00 (Al 5.732 Mg 0.190 Fe 3+ 0.078 ) 6.000 (Si 5.944 Al 0.056 ) 6.000 O 18 (BO 3 ) 3 (OH) 3 (O 0.579 F 0.307 OH 0.115 ) 1.000 for Pribyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe –1 (OH) –1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R 2+ and R 3+ cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R 2+ and R 3+ cations ordered in the Y and Z sites and O disordered in the V and W sites (Pribyslavice).

Description: A bstract This contribution reviews and affords new insights into the crystal chemistry of gadolinite-datolite group (GDG) silicates by re-examination of published and unpublished analytical data. More than 200 electron microprobe analyses (EMPA) and data from both single-crystal and powder X-ray diffraction of 53 samples of GDG silicates were collected to study site occupancy effects on local and long-distance geometry of the crystal structure. Results were achieved by statistical analysis and bond-length and bond-angle calculations. Here, crystal-structure geometry and site occupancy dependence is manifested in the GDG chemical composition and lattice parameters. While the substitution of B for Be at the tetrahedral Z site has the greatest impact on the size of the a parameter, variations in W -site occupancy result in a change in the size of the b parameter. Moreover, the degree of variability in the occupancy of the W site appears to influence the layer-stacking order, which differs between well ordered datolite and weakly ordered gadolinite-subgroup (GSG) minerals. This is documented by c parameter variability. The relationship between the X -site occupancy and lattice parameters is explained by the Jahn-Teller effect, which induces bond-length and angular distortion of the X O 6 octahedron. In addition, the structural arrangement of the X site excludes large cation (such as Ca, Bi, and REE) occupancy without any significant impact on the size of the X O 6 octahedron. Consequently, the formula for minasgeraisite-(Y) with the originally proposed Ca occupancy of the X site is questionable, since no significant difference from hingganite lattice parameters was observed. Thus the mineral requires further structural refinement. The structural arrangement of GDG silicates suggests that two dominant substitution vectors control their chemical composition: CaB(REE) –1 Be –1 and Fe 2+ O 2 (OH) –2 . However, both substitutions are more widespread in GSG minerals than in datolite subgroup (DSG) minerals. This may result from different geochemical properties of their genetic environment. However, there can be structural factors concerning X , W , and Z site occupancy which differentiate the far more chemically variable GSG from DSG.

Description: Green to grayish green tourmaline crystals (up to 10 cm across), with distinct optical zoning, occurs with quartz, blocky albite and muscovite in the Forshammar granitic pegmatite, central Bergslagen province, Sweden. Tourmaline contains inclusions of zircon and xenotime-(Y), and it is cut by veinlets of muscovite and hydroxylbastnäsite-(Ce). Microanalytical and structural data (from the rim) indicate that the tourmaline can be classified as a dravite with moderate Al–Mg disorder at the Y and Z sites. Tourmaline displays chemical zoning that reflects the distribution of Fe, Mg, Al, Ca and Na. The Mg/(Mg+Fe) value is high; it decreases from core (~0.85) to intermediate zone (0.76–0.79), but increases in the rim and vein dravite (0.93). The core has the highest proportion of X -site vacancy and Al content, whereas the intermediate zone is the most enriched in Fe and Na. The rim is slightly depleted in Al and has the highest Na compared to inner zones. Tourmaline veins crosscut the pre-existing tourmaline and are relatively more enriched in Na and Ca. The main compositional variations are driven by Al X Mg –1 Na –1 and AlOMg –1 (OH) –1 substitutions. The Forshammar dravite shows the highest known concentrations of REE from pegmatite tourmaline, ≤1200 ppm REE, ≤210 ppm La, ≤670 ppm Ce; the chondrite-normalized patterns reveal high La N /Yb N (32 to 464) values and strongly negative Eu anomalies (Eu/Eu* = 0.005 to 0.05). The contents of Ti, Mn, Y and REE generally increase at the boundary of the intermediate zone and rim, whereas the contents of Zn, Ga and Sn decrease from the core to the rim. The core is likely a product of an early magmatic process during the late Svecofennian pegmatite formation (~1.8 Ga) as suggested by oscillatory zoning of trace elements. The intermediate zone, rim and tourmaline veins originated during the late magmatic to hydrothermal stage. Hydroxylbastnäsite-(Ce) and muscovite are apparently the final products of the hydrothermal process.