Rossmanite, ⃞(LiAl2)Al6(Si6O18)(BO3)3(OH)4, a new alkali-deficient tourmaline: Description and crystal structure
Rossmanite, ⃞(LiAl2)Al6(Si6O18)(BO3)3(OH)4, a new alkali-deficient tourmaline: Description and crystal structure
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Rossmanite，⃞(LiAl2)Al6(Si6O18)(BO3)3(OH)4，一种新型缺碱电气石：描述和晶体结构
DOI：
10.2138/am-1998-7-822
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发表时间：
1998
影响因子：
3.1
通讯作者：
K. Kyser
中科院分区：
文献类型：
--
作者：
Julie;B.;Selway;M. Novak;Frank;C.;Hawthorne;P. Černý;L. Ottolini;T.;K. Kyser
摘要罗斯曼石是采自捷克摩拉维亚西部Rožná附近的一种新的旅游矿物。它形成浅粉色的柱状晶体，长约25 mm，厚约5 mm，沿沿着c方向延伸，棱柱面上有平行于c方向的条纹。它是脆性的，H= 7，Dmeas = 3.00 g/cm 3，Dcalc = 3.06 g/cm 3。在平面偏振光下，它是无色的。蔷薇辉石为负单轴晶系，t0 = 1.645（1），e = 1.624（1），三方晶系，空间群R3 m，六方晶系a = 15.770（2），c = 7.085（1）<$，V = 1525.8（4）<$3，Z= 3。粉末衍射图中最强的六条X射线衍射线分别为：d = 3.950 nm，I = 100%，（hkl）=（220）; 2.552 nm，93%，（051）; 1.898 nm，72%，（342）; 4.181 nm，58%，（211）; 2.924 nm，56%，（122）;和3.434 μ g，53%，（012）。通过电子探针、西姆斯、H线提取和晶体结构精修的组合进行分析，得到SiO2 38.10重量%，Al 2 O3 44.60，Na 2 O 1.43，Li 2 O = 1.13，B2 O3 = 10.88，H2O = 3.70，F = 0.20，O = F 0.08，总和= 99.96重量%，Fe，Mg，Ca，Mn，Ti，F，K未检测到。公式单元（31个阴离子）是x（57Na0.43）Y（Li0.71Al2.17）zAl6（Si5.92O18）（B2.92O9）（OH）3.83F0.10O0.07，具有理想的端元分子式LiAl 2）Al 6（Si 6 O 18）（BO 3）3（OH）4;因此，可以通过取代xAl1.5Li1.5）（Si 6 O 18）（BO 3）3（OH）4来衍生钙钛矿[Na（Al1.5Li1.5）（Si 6 O 18）（BO 3）3（OH）4]，其中xAl1.5Li1.5 =空位。利用MoKα X射线从单晶中收集的1094个观测（5σ）反射，将rossmanite的晶体结构精修到R指数为1.7%。结构精修证实了X位点的低占有率和Y位点处Li的存在。在O_1和O_2位上存在相当大的位置无序，这是由键价分布的局部变化引起的，与X上的Li-Na无序和Y上的Li-Al无序有关。
Abstract Rossmanite is a new tourmaline species from near Rožná, western Moravia, Czech Republic. It forms pale pink columnar crystals about 25 mm long and 5 mm thick, elongaten along c with striations parallel to c on the prism faces. It is brittle, H= 7, Dmeas = 3.00 g/cm3, Dcalc = 3.06 g/cm3. In plane-polarized light, it is colorless. Rossmanite is uniaxial negative, to = 1.645(1), e = 1.624(1), trigonal, space group R3m, in the hexagonal setting a = 15.770(2), c = 7.085(1) Å, V = 1525.8(4) Å3, Z= 3. The strongest six X-ray diffraction lines in the powder pattern are at d = 3.950 Å with I = 100% for (hkl) = (220); 2.552 Å, 93%, (051); 1.898 Å, 72%, (342); 4.181 Å, 58%, (211); 2.924 Å, 56%, (122); and 3.434 Å, 53%, (012). Analysis by a combination of electron microprobe, SIMS, H-line extraction, and crystal-structure refinement gave SiO2 38.10 wt%, Al2O3 44.60, Na2O 1.43, Li2O = 1.13, B2O3 = 10.88, H2O = 3.70, F = 0.20, O ≡ F 0.08, sum = 99.96 wt%, Fe, Mg, Ca, Mn, Ti, F, K not detected. The formula unit (31 anions) is x(⃞57Na0.43)Y(Li0.71Al2.17)zAl6(Si5.92O18) (B2.92O9)(OH)3.83F0.10O0.07, with the ideal end-member formula ⃞(LiAl2)Al6(Si6O18)(BO3)3(OH)4; thus rossmanite can be derived from elbaite [Na(Al1.5Li1.5)(Si6O18)(BO3)3(OH)4] by the substitution x⃞2 + YAl → xNa2 + YLi, where ⃞ = vacancy. The crystal structure of rossmanite was refined to an R index of 1.7% using 1094 observed (5σ) reflections collected with MoKα X-radiation from a single crystal. The structure refinement confirmed the low occupancy of the X site and the presence of Li at the Y site. There is considerable positional disorder at the O1 and O2 sites induced by the local variations in bond-valence distribution associated with ⃞-Na disorder at X and Li-Al disorder at Y.