ALBERT

Description: The new pyroxenoid barrydawsonite-(Y) occurs at the Merlot Claim, North Red Wine Pluton, Labrador, Canada (62°32'38.54'' W; 54°08'1.37'' N). The host rock is a metamorphosed eudialyte syenite consisting of eudialyte, potassic arfvedsonite, jadeitic aegirine, nepheline, albite and potassium feldspar with accessory Y-bearing pectolite, britholite and steenstrupine. Barrydawsonite-(Y) crystals commonly have discrete thin rims of Y-bearing pectolite. The average empirical formula (based on nine anions p.f.u.) is Na 1.54 Ca 0.74 Mn 0.15 Fe 0.07 Y 0.38 Nd 0.01 Sm 0.01 Gd 0.02 Tb 0.01 Dy 0.04 Ho 0.01 Er 0.02 Yb 0.01 Si 3.00 O 9 H. The simplified formula is Na 1.5 Y 0.5 CaSi 3 O 9 H. Barrydawsonite-(Y) is related to pectolite by the substitution 1/2[Na M 3+ Ca –2 ] ( M 3+ = Y, REE ), and is exceptional in being the only member of the pectolite group that has the structure of the monoclinic M2abc polytype. The crystal structure has been determined in monoclinic space group P 2 1 / a : a = 15.5026(2), b = 7.0233(1), c = 6.9769(1) Å, β = 95.149(1)°, V = 756.58(2) Å 3 ( Z = 4). Final agreement indices are R 1 = 0.038, wR 2 = 0.068, Goof = 1.136. The asymmetric unit of barrydawsonite-(Y) has three metal sites: M (1) = Ca, M (2) = Na 0.5 (Y, REE ) 0.5 , M (3) = Na. M (1) and M (2) are octahedrally-coordinated sites, whereas M (3) is [8]-coordinated as in pectolite and serandite. The structural formula for the empirical composition is M (3) Na 1.00 M (2) (Na 0.50 Y 0.38 REE 0.13 ) =1.01 M (1) (Na 0.04 Ca 0.74 $${\mathrm{Mn}}_{0.15}^{2+}$$ $${\mathrm{Fe}}_{0.07}^{2+}$$ ) =1.00 Si 3 O 9 H. There is excellent agreement between the refined site-scattering values and those calculated based upon the structural formula. Barrydawsonite-(Y) is biaxial (+) with α = 1.612(1), β = 1.617(1), = 1.630(1) (white light) and 2V = 63(1)°. The five strongest peaks in the X-ray powder diffraction pattern are [ d obs ( Å), I obs %, ( hkl )]: [2.905, 100, (023)], [3.094, 30, (210,2I11,1I21,202)], [1.7613, 29, (127,323,040)], [3.272, 27, (2I02,104)], [1.7016, 27, (140,2I27,3I25)].

Description: Khvorovite, ideally $${\mathrm{Pb}}_{4}^{2+}$$ Ca 2 [Si 8 B 2 (SiB)O 28 ]F, is a new borosilicate mineral of the hyalotekite group from the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, Tajikistan. Khvorovite was found in a pectolite aggregate in silexites (quartz-rich rocks). The pectolite aggregate consists mainly of pectolite, quartz and fluorite, with minor aegirine, polylithionite, turkestanite and baratovite; accessory minerals are calcite, pyrochlore-group minerals, reedmergnerite, stillwellite-(Ce), pekovite, zeravshanite, senkevichite, sokolovaite, mendeleevite-(Ce), alamosite, orlovite, leucosphenite and several unknown Cs-silicates. Khvorovite occurs as irregular grains, rarely with square or rectangular sections up to 150 μm, and grain aggregates up to 0.5 mm. Khvorovite is colourless, rarely white, transparent with a white streak, has a vitreous lustre and does not fluoresce under ultraviolet light. Cleavage and parting were not observed. Mohs hardness is 5–5.5, and khvorovite is brittle with an uneven fracture. The measured and calculated densities are 3.96(2) and 3.968 g/cm 3 , respectively. Khvorovite is biaxial (+) with refractive indices ( = 589 nm) α = 1.659(3), β calc. = 1.671(2), = 1.676(3); 2V meas. = 64(3)°, medium dispersion: r 〈 v . Khvorovite is triclinic, space group I 1I, a = 11.354(2), b = 10.960(2), c = 10.271(2) Å, α = 90.32(3), β = 90.00(3), = 90.00(3)°, V = 1278(1) Å 3 , Z = 2. The six strongest lines in the powder X-ray diffraction pattern [ d (Å), I, ( hkl )] are: 7.86, 100, (110); 7.65, 90, (1I01); 7.55, 90, (011); 3.81, 90, (202); 3.55, 90, (301); 2.934, 90, (3I12, 312). Chemical analysis by electron microprobe gave SiO 2 36.98, B 2 O 3 6.01, Y 2 O 3 0.26, PbO 40.08, BaO 6.18, SrO 0.43, CaO 6.77, K 2 O 1.72, Na 2 O 0.41, F 0.88, O=F –0.37, sum 99.35 wt.%. The empirical formula based on 29 (O+F) a.p.f.u. is ( $${\mathrm{Pb}}_{2.76}^{2+}$$ Ba 0.62 K 0.56 Na 0.16 ) 4.10 (Ca 1.86 Sr 0.06 Y 0.04 Na 0.04 ) 2 [Si 8 B 2 (Si 1.46 B 0.65 ) 2.11 O 28 ](F 0.71 O 0.29 ), Z = 2, and the simplified formula is (Pb 2+ ,Ba,K) 4 Ca 2 [Si 8 B 2 (Si,B) 2 O 28 ]F. The crystal structure of khvorovite was refined to R 1 = 2.89% based on 3680 observed reflections collected on a four-circle diffractometer with Mo K α radiation. In the crystal structure of khvorovite, there are four [4]-coordinated Si sites occupied solely by Si with 〈Si–O〉 = 1.617 Å. The [4]-coordinated B site is occupied solely by B, with 〈B–O〉 = 1.478 Å. The [4]-coordinated T site is occupied by Si and B (Si 1.46 B 0.54 ), with 〈T–O〉 = 1.605 Å; it ideally gives (SiB) a.p.f.u. The Si, B and T tetrahedra form an interrupted framework of ideal composition [Si 8 B 2 (SiB)O 28 ] 11– . The interstitial cations are Pb 2+ , Ba and K (minor Na) [ A (11–22) sites] and Ca [ M site]. The two A sites are each split into two subsites ~0.5 Å apart and occupied by Pb 2+ and Ba + K. The [8]-coordinated M site is occupied mainly by Ca, with minor Sr, Y and Na. Khvorovite is a Pb 2+ -analogue of hyalotekite, (Ba,Pb 2+ ,K) 4 (Ca,Y) 2 [Si 8 (B,Be) 2 (Si,B) 2 O 28 ]F and a Pb 2+ -, Ca-analogue of kapitsaite-(Y), (Ba,K) 4 (Y,Ca) 2 [Si 8 B 2 (B,Si) 2 O 28 ]F. It is named after Pavel V. Khvorov (b. 1965), a Russian mineralogist, to honour his contribution to the study of the mineralogy of the Darai-Pioz massif.

Description: Fluor-tsilaisite, NaMn 3 Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 F, is a new mineral of the tourmaline supergroup. It occurs in an aplitic dyke of a LCT-type pegmatite body from Grotta d'Oggi, San Piero in Campo, Elba Island, Italy, in association with quartz, K-feldspar, plagioclase, elbaite, schorl, fluor-elbaite and tsilaisite. Crystals are greenish yellow with a vitreous lustre, sub-conchoidal fracture and white streak. Fluor-tsilaisite has a Mohs hardness of ~7 and a calculated density of 3.134 g/cm 3 . In plane-polarized light, fluor-tsilaisite is pleochroic (O = pale greenish yellow and E = very pale greenish yellow), uniaxial negative. Fluor-tsilaisite is rhombohedral, space group R 3 m , a = 15.9398(6), c = 7.1363(3) Å, V = 1570.25(11) Å 3 , Z = 3. The crystal structure of fluor-tsilaisite was refined to R 1 = 3.36% using 3496 unique reflections collected with Mo K α X-ray intensity data. Crystal-chemical analysis resulted in the empirical formula: X (Na 0.69 0.29 Ca 0.02 ) 1.00 Y ( $${\mathrm{Mn}}_{1.29}^{2+}$$ Al 1.21 Li 0.56 Ti 0.03 ) 6.00 Z Al 6 T (Si 5.98 Al 0.03 ) 6.00 B 2.92 O 27 V (OH) 3 W [F 0.39 (OH) 0.25 O 0.36 ] 1.00 . Comparisons were performed between fluor-tsilaisite and a tsilaisitic tourmaline from the same locality as the holotype specimen. This latter tourmaline sample was selected for this study due to its remarkable composition (MnO = 11.63 wt.%), the largest Mn content found in tourmaline so far. Fluor-tsilaisite is related to tsilaisite through the substitution W F W (OH) and with fluor-elbaite through the substitution Y (Al + Li) 2 Y Mn 2+ , and appears to be a stepwise intermediate during tourmaline evolution from tsilaisite to fluor-elbaite.

Description: When crustal abundance ( A , measured in atomic parts per million) of a chemical element is plotted vs. number of mineral species in which that element is an essential constituent ( S ), a significantly positive correlation is obtained, but with considerable scatter. Repeated exclusion of outliers at the 90% confidence level and re-fitting leads, after the sixth iteration, to a steady state in which 40 of the 70 elements initially considered define a trend with log S = 1.828 + 0.255 log A ( r = 0.96), significantly steeper than the original. Three other methods for reducing the effect of outliers independently reproduce this steeper trend. The ‘diversity index’ D of an element is defined as the ratio of observed mineral species to those predicted from this trend. D separates elements into three groups. More than half of the elements (40 of 70) have D = 0.5–2.0. Apart from these ‘typical’ elements, a group of 15 elements (Sc, Cr, Ga, Br, Rb, In, Cs, La, Nd, Sm, Gd, Yb, Hf, Re and Th) form few species of their own due to being dispersed as minor solid solution constituents, and a hitherto unrecognized group of 15 elements are essential components in unusually large numbers of minerals. The anomalously diverse group consists of H, S, Cu, As, Se, Pd, Ag, Sb, Te, Pt, Au, Hg, Pb, Bi and U, with Te and Bi by far the most mineralogically diverse elements ( D = 22 and 19, respectively). Possible causes and inhibitors of diversity are discussed, with reference to atomic size, electronegativity and Pearson softness, and particularly outer electronic configurations that result in distinctive stereochemistry. The principal factors encouraging mineral diversity are: (1) Particular outer electronic configurations that lead to a preference for unique coordination geometries, enhancing an element's ability to form distinctive chemical compounds and decreasing its ability to participate in solid solutions. This is particularly noteworthy for elements possessing geometrically flexible ‘lone-pair cations’ with an s 2 outer electronic configuration. (2) Siderophilic or chalcophilic geochemical behaviour and intermediate electronegativity, allowing elements to form minerals that are not oxycompounds or halides. (3) Access to a wide range of oxidation states. The most diverse elements can occur as anions, native elements and in more than one cationic valence state.

Description: ‘Clinobarylite’, BaBe 2 Si 2 O 7 , was defined as a monoclinic dimorph of orthorhombic barylite. Subsequently, its crystal structure was also proved to be orthorhombic, differing from barylite in terms of the space group symmetry, Pmn 2 1 instead of Pmnb , and in unit-cell dimensions. Through the order-disorder (OD) theory, the polytypic relationships between ‘clinobarylite’ and barylite are described. ‘Clinobarylite’ corresponds to the MDO 1 polytype, with unit-cell parameters a = 11.650, b = 4.922, c = 4.674 Å, space group Pmn 2 1 ; barylite corresponds to the MDO 2 polytype, with a = 11.67, b = 9.82, c = 4.69 Å, space group Pmnb . The re-examination of the holotype specimen of ‘clinobarylite’ confirmed its orthorhombic symmetry. Its crystal structure has been refined starting from the atomic coordinates calculated for the MDO 1 polytype and the refinement converged to R 1 = 0.0144 for 929 observed reflections [ F o 〉 4 F o ]. Owing to their polytypic relationships, ‘clinobarylite’ and barylite should be conveniently indicated as barylite-1 O and barylite-2 O , respectively; the name ‘clinobarylite’ should be discontinued. This new nomenclature of the barylite polytypes has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 13-E).