The Rietveld Refinement of Beryls from Pegmatitic System at Piława Górna, Góry Sowie Block, SW Poland

The studied beryl crystals came from the Julianna pegmatitic system exposed in the Dolnoslaskie Surowce Skalne S.A. quarry at Piława Górna. This mineral occurs here in various forms and colours (green, yellow, white, pinkish and blue) in almost all pegmatite bodies. The paper describes the relationship between the structure and chemical composition of different coloured beryl crystals

Holtite and Dumortierite from the Szklary Pegmatite, Lower Silesia, Poland

The Szklary holtite is represented by three compositional varieties: (I) Ta-bearing (up to 14.66 wt.% Ta(2)O(5)), which forms homogeneous crystals and cores within zoned crystals; (2) Ti-bearing (up to 3.82 wt.% TiO(2)), found as small domains within the core; and (3) Nb-bearing (up to 5.30 wt.% Nb(2)O(5),) forming the rims of zoned crystals. All three varieties show variable Sb+As content, reaching 19.18 wt.% Sb(2)O(3) (0.87 Sb a.p.f.u.) and 3.30 wt.% As(2)O(3) (0.22 As a.p.f.u.) in zoned Ta-bearing holtite, which constitutes the largest Sb+As content reported for the mineral. The zoning in holtite is a result of Ta-Nb fractionation in the parental pegmatite-forming melt together with contamination of the relatively thin Szklary dyke by Fe, Mg and Ti. Holtite and the As- and Sb-bearing dumortierite, which in places overgrows the youngest Nb-bearing zone, suggest the following crystallization sequence: Ta-bearing holtite -\u3e Ti-bearing holtite -\u3e Nb-bearing holtite -\u3e As- and Sb-bearing, (Ta,Nb,Ti)-poor dumortierite -\u3e As- and Sb-dominant, (Ta,Nb,Ti)-free dumortierite-like mineral (16.81 wt.% As(2)O(3) and 10.23 wt.% Sb(2)O(3)) with (As+Sb) \u3e Si. The last phase is potentially a new mineral species, Al(6)rectangle B(Sb,As)(3)O(15). or Al(5)rectangle(2)B(Sb,As)(3)O(12)(OH)(3), belonging to the dumortierite group. The Szklary holtite shows no evidence of clustering of compositions around \u27holtite I\u27 and \u27holtite II\u27. Instead, the substitutions of Si(4+) by Sb(3+)+As(3+) at the Si/Sb sites and of Ta(5+) by Nb(5+) or Ti(4+) at the Al(l) site suggest possible solid solutions between: (1) (Sb,As)-poor and (Sb,As)-rich holtite; (2) dumortierite and the unnamed (As+Sb)-dominant dumortierite-like mineral; and (3) Ti-bearing dumortierite and holtite, i.e. our data provide further evidence for miscibility between holtite and dumortierite, but leave open the question of defining the distinction between them. The Szklary holtite crystallized from the melt along with other primary Ta-Nb-(Ti) minerals such as columbite-(Mn), tantalite-(Mn), stibiotantalite and stibiocolumbite as the availability of Ta decreased. The origin of the parental melt can be related to anatexis in the adjacent Sowie Mountains complex, leading to widespread migmatization and metamorphic segregation in pelitic-psammitic sediments metamorphosed at similar to 390-380 Ma

The Crystal Chemistry of Holtite

Holtite, approximately (Al,Ta,square)Al(6)(BO(3))(Si,Sb(3+),As(3+))(Sigma 3)O(12)(O,OH,square)(Sigma 3), is a member of the dumortierite group that has been found in pegmatite, or alluvial deposits derived from pegmatite, at three localities: Greenbushes, Western Australia; Voron\u27i Tundry, Kola Peninsula, Russia; and Szklary, Lower Silesia, Poland. Holtite can contain \u3e30 wt.% Sb(2)O(3), As(2)O(3), Ta(2)O(5), Nb(2)O(5), and TiO(2) (taken together), but none of these constituents is dominant at a crystallographic site, which raises the question whether this mineral is distinct from dumortierite. The crystal structures of four samples from the three localities have been refined to R(1) = 0.02-0.05. The results show dominantly: Al, Ta, and vacancies at the Al(1) position; Al and vacancies at the Al(2), (3) and (4) sites; Si and vacancies at the Si positions; and Sb, As and vacancies at the Sb sites for both Sb-poor (holtite I) and Sb-rich (holtite II) specimens. Although charge-balance calculations based on our single-crystal structure refinements suggest that essentially no water is present, Fourier transform infrared spectra confirm that some OH is present in the three samples that could be measured. By analogy with dumortierite, the largest peak at 3505-3490 cm(-1) is identified with OH at the O(2) and O(7) positions. The single-crystal X-ray refinements and FTIR results suggest the following general formula for holtite: Al(7-[5x+y+z]/3)(Ta,Nb)(x)square([2x+y+z]/3)BSi(3-y)(Sb,As)(y)O(18-y-z)(OH)(z), where x is the total number of pentavalent cations, y is the total amount of Sb + As, and z \u3c= y is the total amount of OH. Comparison with the electron microprobe compositions suggests the following approximate general formulae Al(5.83)(Ta,Nb)(0.50)square(0.67)BSi(2.50)(Sb,As)(0.50)O(17.00)(OH)(0.50) and Al(5.92)(Ta,Nb)(0.25)square(0.83)BSi(2.00)(Sb,As)(1.00) O(16.00)(OH)(1.00) for holtite I and holtite II respectively. However, the crystal structure refinements do not indicate a fundamental difference in cation ordering that might serve as a criterion for recognizing the two holtites as distinct species, and anion compositions are also not sufficiently different. Moreover, available analyses suggest the possibility of a continuum in the Si/(Sb + As) ratio between holtite I and dumortierite, and at least a partial continuum between holtite I and holtite II. We recommend that use of the terms holtite I and holtite II be discontinued

The dumortierite supergroup. II. Three new minerals from the Szklary pegmatite, SW Poland: Nioboholtite, (Nb_(0.6)〈_(0.4))Al_6Bsi_3O_(18), titanoholtite, (Ti_(0.75)〈_(0.25))Al_6Bsi_3O_(18), and szklaryite 〈Al_6Bas^(3+)_ 3O_(15)

Three new minerals in the dumortierite supergroup were discovered in the Szklary pegmatite, Lower Silesia, Poland. Nioboholtite, endmember (Nb_(0.6)〈_(0.4))Al_6B_3Si_3O_(18), and titanoholtite, endmember (Ti_(0.75)〈_(0.25))Al_6B_3Si_3O_(18), are new members of the holtite group, whereas szklaryite, endmember 〈Al_6Bas^(3+)_ 3O_(15), is the first representative of a potential new group. Nioboholtite occurs mostly as overgrowths not exceeding 10 μm in thickness on cores of holtite. Titanoholtite forms patches up to 10 μm across in the holtite cores and streaks up to 5 μm wide along boundaries between holtite cores and the nioboholtite rims. Szklaryite is found as a patch ∼2 μm in size in As- and Sb- bearing dumortierite enclosed in quartz. Titanoholtite crystallized almost simultaneously with holtite and other Ta-dominant minerals such as tantalite-(Mn) and stibiotantalite and before nioboholtite, which crystallized simultaneously with stibiocolumbite during decreasing Ta activity in the pegmatite melt. Szklaryite crystallized after nioboholtite during the final stage of the Szklary pegmatite formation. Optical properties could be obtained only from nioboholtite, which is creamy-white to brownish yellow or grey-yellow in hand specimen, translucent, with a white streak, biaxial (–), n_α = 1.740 – 1.747, n_β ∼ 1.76, n_γ ∼ 1.76, and Δ < 0.020. Electron microprobe analyses of nioboholtite, titanoholtite and szklaryite give, respectively, in wt.%: P_2O_5 0.26, 0.01, 0.68; Nb_2O_55.21, 0.67, 0.17; Ta_2O_5 0.66, 1.18, 0.00; SiO_2 18.68, 21.92, 12.78; TiO_2 0.11, 4.00, 0.30; B_2O_3 4.91, 4.64, 5.44; Al_2O_3 49.74, 50.02, 50.74; As_2O_3 5.92, 2.26, 16.02; Sb_2O_3 10.81, 11.48, 10.31; FeO 0.51, 0.13, 0.19; H_2O (calc.) 0.05, –, –, Sum 96.86, 96.34, 97.07, corresponding on the basis of O = 18–As–Sb to {(Nb_(0.26)Ta_(0.02)〈_(0.18)) (Al_(0.27)Fe_(0.05)Ti_(0.01))〈_(0.21)}_(Σ1.00)Al_6B_(0.92){Si_(2.03)P_(0.02)(Sb_(0.48)As_(0.39)Al_(0.07)}_(Σ3.00)(O_(17.09)OH_(0.04)〈_(0.87))_(Σ18.00), {(Ti_(0.32) Nb_(0.03)Ta_(0.03)〈_(0.10) )(Al_(0.3 5) Ti_(0.01) Fe_(0.01))〈_(0.15)}_(Σ1.00) Al_6 B_(0.86) {Si_(2.36) (Sb_(0.51) As_(0.14) )}_(Σ3.01)(O_(17.35)〈_(0.65))_(Σ18.00) and {〈_(0.53) (Al_(0.41) Ti_(0.02) Fe_(0.02))(Nb_(0.01)〈_(0.01) )}_(Σ1.00)Al_6 B_(1.01) {(As_(1.07) Sb_(0.47) Al_(0.03)) Si_(1.37) P_(0.06)}_(Σ3.00)(O_(16.46)〈_(1.54))_(Σ18.00). Electron backscattered diffraction indicates that the three minerals are presumably isostructural with dumortierite, that is, orthorhombic symmetry, space group Pnma (no. 62), and unit-cell parameters close to a = 4.7001, b = 11.828, c = 20.243 Å, with V = 1125.36 Å^3 and Z = 4; micro-Raman spectroscopy provided further confirmation of the structural relationship for nioboholtite and titanoholtite. The calculated density is 3.72 g/cm^3 for nioboholtite, 3.66 g/cm^3 for titanoholtite and 3.71 g/cm^3 for szklaryite. The strongest lines in X-ray powder diffraction patterns calculated from the cell parameters of dumortierite of Moore and Araki (1978) and the empirical formulae of nioboholtite, titanoholtite and szklaryite are [d, Å, I (hkl)]: 10.2125, 67, 46, 19 (011); 5.9140, 40, 47, 57 (020); 5.8610, 66, 78, 100 (013); 3.4582, 63, 63, 60 (122); 3.4439, 36, 36, 34 (104); 3.2305, 100, 100, 95 (123); 3.0675, 53, 53, 50 (105); 2.9305, 65, 59, 51 (026); 2.8945, 64, 65, 59 (132), respectively. The three minerals have been approved by the IMA CNMNC (IMA 2012-068, 069, 070) and were named for their relationship to holtite and occurrence in the Szklary pegmatite, respectively

The dumortierite supergroup. I. A new nomenclature for the dumortierite and holtite groups

Although the distinction between magnesiodumortieite and dumortierite, i.e. Mg vs. Al dominance at the partially vacant octahedral Al1 site, had met current criteria of the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) for distinguishing mineral species, the distinction between holtite and dumortierite had not, since Al and Si are dominant over Ta and (Sb, As) at the Al1 and two Si sites, respectively, in both minerals. Recent studies have revealed extensive solid solution between Al, Ti, Ta and Nb at Al1 and between Si, As and Sb at the two Si sites or nearly coincident (As, Sb) sites in dumortierite and holtite, further blurring the distinction between the two minerals. This situation necessitated revision in the nomenclature of the dumortierite group. The newly constituted dumortierite supergroup, space group Pnma (no. 62), comprises two groups and six minerals, one of which is the first member of a potential third group, all isostructural with dumortierite. The supergroup, which has been approved by the CNMNC, is based on more specific end-member compositions for dumortierite and holtite, in which occupancy of the Al1 site is critical. (1) Dumortierite group, with Al1 = Al^(3+), Mg^(2+) and 〈, where 〈 denotes cation vacancy. Charge balance is provided by OH substitution for O at the O2, O7 and O10 sites. In addition to dumortierite, endmember composition AlAl_6Bsi_3O_(18), and magnesiodumortierite, endmember composition MgAl_6Bsi_3O_(17)(OH), plus three endmembers, “hydroxydumortierite”, 〈Al_6Bsi_3O_(15)(OH)_3 and two Mg-Ti analogues of dumortierite, (Mg_(0.5)Ti_(0.5))Al_6Bsi_3O_(18) and (Mg_(0.5)Ti_(0.5))Mg_2Al_4Bsi_3O_(16)(OH)_2, none of which correspond to mineral species. Three more hypothetical endmembers are derived by homovalent substitutions of Fe^(3+) for Al and Fe^(2+) for Mg. (2) Holtite group, with Al1 = Ta^(5+), Nb^(5+), Ti^(4+) and 〈. In contrast to the dumortierite group, vacancies serve not only to balance the extra charge introduced by the incorporation of pentavalent and quadrivalent cations for trivalent cations at Al1, but also to reduce repulsion between the highly charged cations. This group includes holtite, endmember composition (Ta_(0.6)〈_(0.4))Al_6Bsi_3O_(18), nioboholite (2012-68), endmember composition (Nb_(0.6)〈_(0.4_)Al_6Bsi_3O_(18), and titanoholtite (2012-69), endmember composition (Ti_(0.75)〈_(0.25))Al_6Bsi_3O_(18). (3) Szklaryite (2012-70) with Al1 = 〈 and an endmember formula 〈Al_6Bas^(3+)_ 3O_(15). Vacancies at Al1 are caused by loss of O at O2 and O7, which coordinate the Al1 with the Si sites, due to replacement of Si^(4+) by As^(3+) and Sb^(3+), and thus this mineral does not belong in either the dumortierite or the holtite group. Although szklaryite is distinguished by the mechanism introducing vacancies at the Al1 site, the primary criterion for identifying it is based on occupancy of the Si/As, Sb sites: (As^(3+) + Sb^(3+)) > Si^(4+) consistent with the dominant-valency rule. A Sb^(3+) analogue to szklaryite is possible

The future climate characteristics of the Carpathian Basin based on a regional climate model mini-ensemble

Four regional climate models (RCMs) were adapted in Hungary for the dynamical downscaling of the global climate projections over the Carpathian Basin: (i) the ALADIN-Climate model developed by Météo France on the basis of the ALADIN short-range modelling system; (ii) the PRECIS model available from the UK Met Office Hadley Centre; (iii) the RegCM model originally developed at the US National Center for Atmospheric Research, is maintained at the International Centre for Theoretical Physics in Trieste; and (iv) the REMO model developed by the Max Planck Institute for Meteorology in Hamburg. The RCMs are different in terms of dynamical model formulation, physical parameterisations; moreover, in the completed simulations they use different spatial resolutions, integration domains and lateral boundary conditions for the scenario experiments. Therefore, the results of the four RCMs can be considered as a small ensemble providing information about various kinds of uncertainties in the future projections over the target area, i.e., Hungary. After the validation of the temperature and precipitation patterns against measurements, mean changes and some extreme characteristics of these patterns (including their statistical significance) have been assessed focusing on the periods of 2021&ndash;2050 and 2071&ndash;2100 relative to the 1961&ndash;1990 model reference period. The ensemble evaluation indicates that the temperature-related changes of the different RCMs are in good agreement over the Carpathian Basin and these tendencies manifest in the general warming conditions. The precipitation changes cannot be identified so clearly: seasonally large differences can be recognised among the projections and between the two periods. An overview is given about the results of the mini-ensemble and special emphasis is put on estimating the uncertainties in the simulations for Hungary