From structure topology to chemical composition. XX. Titanium silicates : The crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, a Group-II TS-block mineral

The crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, from Mbolve Hill, Mkushi River area, Central Province, Zambia (holotype material) has been refined on a twinned crystal to R1 = 1.88% on the basis of 4539 [|F| > 4\u3c3|F|] reflections. Hejtmanite is triclinic, C-1, a = 10.716(2), b = 13.795(3), c = 11.778 (2) \uc5, \u3b1 = 90.07(3), \u3b2 = 112.24(3),\u3b3= 90.03(3)\ub0, V = 1612(2) \uc53. Chemical analysis (electron microprobe) gives: Ta2O5 0.09, Nb2O5 1.27, ZrO2 0.65, TiO2 14.35, SiO2 23.13, BaO 26.68, SrO 0.19, FeO 11.28, MnO 15.12, Cs2O 0.05, K2O 0.33, F 3.82, H2Ocalc. 1.63, O = F-1.61, total 97.10 wt.%, where the H2O content was calculated from the crystal-structure refinement, with (OH + F) = 4 apfu. The empirical formula, calculated on the basis of 20 (O + F) anions, is of the form AP2 MO4 MH2 (Si2O7)2(XO)4(XP)2, Z=4: (Ba1.82K0.07 Sr0.02)\u3a31.91(Mn2.33Fe21 1:65Zr0.04Mg0.03)\u3a33.95(Ti1.88Nb0.10Zr0.02)\u3a32(Si2.02O7)2O2[(OH)1.89 F0.11]\u3a32F2. The crystal structure is a combination of a TS (Titanium Silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The topology of the TS block is as in Group-II TS-block minerals: Ti (+ Nb) = 2 apfu per (Si2O7)2 [as defined by Sokolova (2006)]. In the O sheet, five [6]MO sites are occupied mainly by Mn, less Fe2+ and minor Zr and Mg, with = 2.198 \uc5 (\u3c6 = O,OH), ideally giving Mn4 apfu. In the H sheet, two [6]MH sites are occupied mainly by Ti, with = 1.962 \uc5 (\u3c6 = O,F), ideally giving Ti2 apfu; four [4]Si sites are occupied by Si, with = 1.625 \uc5. TheMH octahedra and Si2O7 groups constitute the H sheet. The two [12]Ba-dominant AP(1,2) sites, with = 2.984 \uc5 (\u3c6 = O, F), ideally give Ba2 apfu. Two XOM(1,2) and two XOA (1,2) sites are occupied by O atoms and OH groups with minor F, respectively, ideally giving (XO)4 = (XM O)2 + (XAO)2=O2(OH)2 pfu. Two XP M(1,2) sites are occupied by F, giving F2 apfu. TS blocks link via a layer of Ba atoms which constitute the I block. Simplified and end-member formulae of hejtmanite are Ba2(Mn,Fe2+)4Ti2 (Si2O7)2O2(OH,F)2 F2 and Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, Z = 4. Hejtmanite is a Mn-analogue of bafertisite, Ba2Fe2+4 Ti2(Si2O7)2O2(OH)2F2

Fluorapophyllite-(Cs), CsCa₄(Si₈O₂₀)F(H₂O)₈, a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, Northern Tajikistan

Fluorapophyllite-(Cs) (IMA 2018-108a), ideally CsCa4(Si8O20)F(H2O)(8), is an apophyllite-group mineral from the moraine of the Darai-Pioz glacier, Tien-Shan, Northern Tajikistan. Associated minerals are quartz, pectolite, baratovite, aegirine, leucosphenite, pyrochlore, neptunite, fluorapophyllite-(K), and reedmergnerite. Fluorapophyllite-(Cs) is a hydrothermal mineral. It is colorless and has a vitreous luster and a white streak. Cleavage is perfect; it is brittle and has a stepped fracture. Mohs hardness is 4.5-5. D-meas. = 2.54(2) g/cm(3), D-calc. = 2.513 g/cm(3). Fluorapophyllite-(Cs) is unixial (+) with refractive indices (lambda = 589 nm) omega = 1.540(2), epsilon = 1.544(2). It is non-pleochroic. Chemical analysis by electron microprobe gave SiO2 48.78, Al2O3 0.05, CaO 22.69, Cs2O 10.71, K2O 1.13, Na2O 0.04, F 1.86, H2Ocalc. 14.61, -O=F2 -0.78, sum 99.09 wt.%; H2O was calculated from crystal-structure analysis. The empirical formula based on 29 (O + F) apfu, H2O = 8 pfu, is (Cs0.75K0.24)Sigma(0.99)(Ca3.99Na0.01)Sigma(4)(Si8.01Al0.01)Sigma 8.02O20.03F0.97(H2O)8, Z = 2. The simplified formula is (Cs,K)(Ca,Na)(4)(Si,Al) 8 O20F(H2O)(8). Fluorapophyllite-(Cs) is tetragonal, space group P4/mnc, a 9.060(6), c 15.741(11) angstrom, V 1292.10(19) angstrom(3). The crystal structure has been refined to R-1 = 4.31% based on 498 unique (F-o > 4 sigma F) reflections. In the crystal structure of fluorapophyllite-(Cs), there is one [4] T site occupied solely by Si,,T-O. = 1.615 angstrom. SiO4 tetrahedra link to form a (Si8O20)(8-)sheet perpendicular to [001]. Between the Si-O sheets, there are two cation sites: A and B. The A site is coordinated by eight H2O groups [O(4) site], A-O(4) = 3.152(4) angstrom; the A site contains Cs(0.75)K(0.24)A(0.01 square 0.01), ideally Cs apfu. The Cs-O bond length of 3.152 angstrom is definitely larger than the K-O bond length of 2.966-2.971 angstrom in fluorapophyllite-(K), KCa4(Si8O20)F(H2O)8. The [7]B site contains Ca3.99Na0.01, ideally Ca-4 apfu; < B-phi > = 2.417 angstrom (phi = O, F, H2O). The Si-O sheets connect via A and B polyhedra and hydrogen bonding; two H atoms have been included in the refinement. Fluorapophyllite-(Cs) is isostructural with fluorapophyllite-(K). Fluorapophyllite-(Cs) is a Cs-analogue of fluorapophyllite-(K)

Interfaces in metamict titanite: the macroscopic mechanical properties after stepwise annealing

Elastic material properties of metamict titanite (sample E2312) during thermally induced stepwise recrystallization are measured using nanoindentation. Changes of the elastic modulus (E) and the hardness (H) are related to increasing long-range order and vanishing amorphous interface areas. Metamict titanite shows H and E values close to titanite glass. H decreases on annealing until ca. 950 K to 9.08 GPa and increases at higher temperatures, while E increases continuously on annealing up to ca. 168.4 GPa at 1220 K. Crystalline titanite from Rauris shows strong anisotropy and H and E values are clearly larger than those of E2312

Women and the information society: barriers and participation

Paper presented to the Women’s Is-sues Section of IFLA at the 68th IFLA General Conference, held in Glasgow, Scotland, from 18–24 August 2002. Reviews the literature on the topic of women, the information society and the Internet. Also presents selected results of Masters’ research projects undertaken in the Department of Information Science at Loughborough University, United Kingdom. Discusses female access to the Internet and explores some of the barriers that may prevent women having the same access as men. Examines differences in male and female Internet use. The negative aspects of the Internet for women are very often emphasized, but there are positive reasons for women to use the Internet and advantages to this method of computer-mediated communication for women. The concept of Cyberfeminism is discussed. Concludes that although there are negative sides to the technology, women must engage with the Internet if they are to help shape the Information Society

Resistance of tomato plant genotypes with high foliar allelochemical contents to the leafminer Liriomyza trifolii

ABSTRACT: The objective of this study was to assess the resistance of tomato genotypes with high foliar levels of allelochemicals to the leafminer Liriomyza trifolii. Eight tomato genotypes with contrasting levels of three different alellochemicals were tested for leafminer resistance: the TOM-687 and TOM-688 lines, which are both rich in acylsugar; ZGB-703 and ZGB-704, which are rich in zingiberene; BPX-365G-899-07-04-02 and BPX-367E-238-02, which are rich in 2-tridecanone; and 2 standard commercial hybrids (Deborah Max and Bravo F1) with low-allelochemical content. Thirty days after being transplanted, nine potted plants of each of the treatments were transferred to a phytotron chamber, into which 1600 unsexed leafminer adults from a mass rearing were released. The number of mines and the percentage of leaves and leaflets attacked (= with the presence of punctures) were evaluated. Six days later, the number of pupae was recorded. The genotypes with high levels of acylsugar were associated with higher levels of resistance to leaf miner L. trifolii, through antixenosis and antibiosis mechanisms. At least one of the 2-tridecanone-rich lines (BPX -365G-899-07-04-02) showed some level of resistance via an antibiosis mechanism

Predicting alpha diversity of African rain forests: models based on climate and satellite-derived data do not perform better than a purely spatial model

Our aim was to evaluate the extent to which we can predict and map tree alpha diversity across broad spatial scales either by using climate and remote sensing data or by exploiting spatial autocorrelation patterns in tropical rain forest, West Africa and Atlantic Central Africa