锆石形态标型特征及标型生长机制探讨

本文在系统总结归纳不同研究者对锆石形态标型特征的研究成果基础上，重点从晶体生长、晶体化学和地球化学理论为重点探讨了锆石形态标型特征的生长机制。研究表明：锆石晶体结构中不同的面网方向，其平面内的原子组成、比例、化学键联结和键力以及面网间距和密度都是有差别的，由此决定了锆石晶体在不同的结晶介质条件下，不同面网的生长速度发生改变，生成相应的晶形。例如，尽管碱性元素并不进入锆石晶格，但它们可以影响Ｚｒ、Ｓｉ、Ｏ离子的扩散速度，但是富钾和富钠的介质对锆石晶形发育的影响是有差别的，表现为：在富钾的介质中，将导致柱面的法向生长速度较锥面快得多，而锥面中，｛１１１｝的法向生长又较｛３１１｝快，由此决定了形成以｛３１１｝锥为主的双锥状晶体；在富钠的介质中，柱面和锥面都有一定程度的发育，但前者弱于后者，而柱面中，｛１００｝的法向生长较｛１１０｝慢，由此决定了形成以｛１００｝柱和｛１１１｝锥为主的短柱锥状晶体。根据类似方法，论证了其它形态标型特征的客观性，从而揭示了标型之间的内在联系和本质，展示了花岗岩研究中锆石形态标型特征应用推广的前景，也可为单颗粒锆石定年研究提供更多的分析应用价值     

晶体生长基元的稳定能与闪锌矿的结晶形态

本文从负离子配位多面体生长基元模型出发，建立了闪锌矿晶体生长基元的数学模型，通过对闪锌矿晶体生长基元稳定能的计算，讨论了闪锌矿的结晶形态和生长机理     

蒙山矿的晶体结构

本文对产于我国山东的新矿物蒙山矿(Mathiasite)进行了晶体结构精测。蒙山矿的晶体化学式为:(K、Ca、Sr)(Ti、cr、Fe、Mg、Zr)_(21)O_(38),三方晶系,空间群R,晶胞参数:a_o=10.3722,c_o=20.7161(六方定向),a_R=9.1403,a=69.187°(菱面体定向)。应用RASA-5RP自动转靶四圆单晶衍射仪,对蒙山矿收集了独立的1554个衍射强度。经结构解析和修正,求得了晶体中各原子的坐标、温度因子、占位度。并计算了原子的间距和键角。结构修正的偏离因子: R=0.047。蒙山矿产于金伯利岩中,形成于高温高压下。通过结构测定,确定了该矿物中Ti、Cr、Mg、K等元素的配位形式,特别是查明了Zr在这种以Ti为主的复杂氧化物中有独立的结晶学位置,并有缺席现象。以上研究成果丰富了金伯利岩中金属副矿物的矿物学和晶体化学内容。     

Crystal structure of daqingshanite

Daqinshanite, a new mineral recently discovered in China, is a kind of strontium-rare earth-bearing phosphate-carbonate. The ideal formula is: (Sr, Ca, Ba), RF(PO₄)(CO₃)₃. The mineral belongs to the trigonal system. The intensity data were collected with a single-crystal four-circle diffractometer. The lattice parameters are given as:a=10.058(±0.002) Å;c=9.225(±0.003) Å. Space group=R3m,Z=3. The crystal structure was solved by Patterson and electron density synthesis methods. The least-squares refinement led to a final conventional factorR=0.079. Crystal structural analysis shows that daqingshanite is of calcite-type structure and the ordered model of cations is similar to that of huntite (Mg₃Ca(CO₃)₄).     

Crystal chemistry of Fe-Mg-carpholites

A chemical and X-ray investigation of the Fe-Mg-carpholites of Crete/Greece reveals a large variation in their Fe²⁺/(Fe²⁺+Mg) ratios (0.68 to 0.05). The lattice constants a and b depend linearly on this parameter, and the magnitude of the effect is comparable to that encountered in pyroxenes. The similar behaviour of the lattice dimensions of both these minerals is explained by comparing their structures and pointing out the salient crystal chemical similarities.     

Crystal concentration in ignimbrites

A comparison of the crystal contents of selected sieve grades from 9 ignimbrites, with the yield of crystals from crushed pumice, shows that on average a tenfold concentration of crystals has taken place in the ignimbrites. This is explained by the selective loss of pumice by an amount equal to at least the present bulk of the samples studied. The pumice is thought to have been lost above the vent or the moving pyroclastic flow, though there is a possibility, yet untested, that it may be contained in the distil part of the ignimbrites.This paper also further characterises the relatively well-sorted basal layer, and the pipes (interpreted as due to primary fumaroles) which cut some ignimbrites. Basal layer and pipes show an even greater concentration of crystals than the body of the ignimbrites.One corollary of this study is that doubt is placed on the value of making chemical analyses of ignimbrites, the composition of which is likely to depart appreciably from that of the eruptive magma.     

Crystal structure of xinganite

Xinganite is a new REE-Be-rich silicate discovered in China. Its ideal formula is: (Y, Ce)Be SiO₄ OH. The mineral is of monoclinic system. The intensity data were collected with a single-crystal four-circle diffractometer. The lattice parameters are: a=4.7681 (± 0.00263) Å,b=7.7657 (± 0.00686) Å, c=9.9301 (± 0.00639) Å; α =90°, β=90.171° (±0.0053°), γ=90° space group p2¹/c;,Z=4. The crystal structure has been determined by direct methods and electron density synthesis methods. The least squares refinement gave a final discrepancy indexR=0.086. The crystal structural analysis shows that xinganite is of datolite-type structure.     

The Crystal Structure of Lisiguangite

The crystal structure of lisiguangite,CuPtBiS3,from Yanshan mountains,Chengde Prefecture,Hebei Province,China has been determined by single crystal X-ray diffraction.It belongs to orthorhombic space group P2_12_12_1 with a = 7.7372(15) A,b = 12.844(3) A,c = 4.9062(10) A,V =487.57(17) A~3,Z = 4.The final full-matric least-square refinement on F2 converged with Rl = 0.0495 and wR2 = 0.0992 for 704 observed reflections[I≥2σ(I)].Lisiguangite is the isomorph of known CuNiSbS_3 and CuNiBiS_3· Pt~(2+) and Bi~(3+) have the distorted octahedral coordination enviroments composed of two metal and four S and Cu~(+2) has a distorted tetrahedral coordination environment with four S atoms.Each S atom is surrounded by four metals to give a tetrahedral environment.The crystal structure is a complex 3 dimensional network.     

Crystal chemistry of Fe-containing sphalerites

 Cell dimensions and solvus properties of Fe-containing sphalerites, depending on temperature and sulfur fugacity, were investigated using equilibrated powdered materials synthesized from elements and binary sulfides under vacuum. The Fe solvus in sphalerite, determined by optical microscopy and microprobe analysis, are directly correlated with increasing temperature and decreasing sulfur fugacity controlled by solid-state buffers. The increase of lattice parameters with Fe correlates with an increase of FeS independent of sulfur fugacity up to 10 mol% FeS within ZnS. Above about 10 mol% the lattice parameters are strongly depending on the sulfur fugacity controlled Fe³⁺/Fe²⁺ ratios. The Fe³⁺/Fe²⁺ ratios determined by Moessbauer spectroscopy and involving metal vacancies depend on the sulfur fugacity. The critical Fe²⁺ content determined by experimental simulations as well as the minimal Fe³⁺/ Fe²⁺ ratios agree with the required minimal Fe content for CuFeS₂-DIS in sphalerite. The critical Fe²⁺ content also agrees with the change of Moessbauer signal from a singlet to a doublet for Fe²⁺ containing sphalerite. Pyrrhotite exsolutions in sphalerite caused by higher sulfur fugacity show orientationally intergrown with the sphalerite matrix. Density data calculated from lattice parameters and composition are compared with experimental density measurements. Received: 25 April 2001 / Accepted: 14 February 2003     

Crystal settling in a sill

A quantitative model for the settling of a spherical body in a Newtonian fluid is developed and is applied to the distribution of phenocrystic olivine in a differentiated dolerite sill. Satisfactory agreement was obtained between the model calculation and the observed modal olivine distribution in the sill.     

Study on the Crystal of Daomanite

It was not possible to carry out a complete analyses of crystal, as the experiment by Ding and Shi et al.. It's analysis precision R=0.25 or more big than this, which value are not satisfied for single crystal study, but we through many test and found the best: [R(int)=14.5%]. The final fullmatix least-squares refinement on F2 converged to R1=0.0791 and wR2=0.1864 for 704 observed reflections [I 3 2s(I)]. Daomanite is orthorhombic system, space group Cmc21, a=3.7520(8))?, b=15.844(4) ?, c=5.8516(12) ?, α=β=γ=90°. V=347.86(14)?3, Z=4. Daomanite chemical formula is Cu Pt AsS 2. Idealized composition Me+M2+M2+S2=CuS ·PtA s S. There is no other similar mineral in the world.     

晶体中的空位测量

夫伦克尔［１］提出晶体中的一些原子会自发地离开它们的晶格的格点位置,从而形成一部分空着的晶格位置,即空位,将保持在平衡态。这一观点,首次解释了物质如何在晶体中输运的问题,因为邻近的原子会掉进空位中,使空位本身迁移了。有一类叫快离子导体的导电性是由离子的运动产生的。假如所有的离子都是按照理想状态规规矩矩地处于晶格点阵的位置上,就不可能理解离子怎样通过格点而运动。只有假设晶格点阵中存在空位和原子可能处于点阵中的间隙位置上,才能解释固体中的离子的运动。此后,晶体的空位成为固体物理、固体化学、冶金学乃至…     

提高人造金刚石单晶质量

从设备的更新，原材料质量的提高，人造金刚石合成工艺的改进等方面，对如何提高金刚石单晶质量进行了探讨。     

Crystal chemistry of Sc-bearing synthetic diopsides

Scandium substitution in the diopside structure was studied by single-crystal X-ray diffraction on a series of synthetic diopside samples. These diopsides were doped with increasing amounts of Sc³⁺ through a coupled substitution involving ^M1(Sc³⁺)₁ ^M2[] ₁ ^T (B)₁ ^M1(Mg²⁺)_?1 ^M2(Ca²⁺)_?1 ^T(Si⁴⁺)_?1 exchange, whereby charge compensation is achieved by vacancies at the M2 sites and B at the tetrahedral sites. The substitution of scandium for magnesium at the M1 site results in an increase in volume and distortion of the M1O₆ polyhedron. The accompanying creation of vacancies at the M2 sites causes an increase in the M2 polyhedral volume. The modifications of the M1 and M2 polyhedra result in an increase of the polyhedral strip along the b lattice direction and a straightening of the tetrahedral chain. The geometrical modification of the M1 polyhedron due to scandium incorporation is comparable to those observed when similar amounts of Ti³⁺/Ti⁴⁺ substitute for Mg in the diopside structure, suggesting a structural control on the solubility of Sc and Ti in diopside that may influence the extent of the solid solutions between the Sc and Ti end-members.     

Crystal structure of magnetite under pressure

The crystal structure and the unit-cell parameters of magnetite have been studied at room temperature up to a pressure of 4.5 GPa using a diamond anvil cell and a four-circle X-ray diffractometer. The isothermal bulk modulus (K _T ) and its pressure derivative (K' _T ) determined by fitting the pressure-volume data to the Murnaghan equation of state are 181(2) GPa and 5.5(15), respectively. The positional parameter u does not vary significantly over the pressure range of this study. The linear compressibilities of the interatomic distances and the bulk moduli of the polyhedra have been calculated from the pressure dependences of the unit-cell edge a and the u parameter. The Bloch equation has been modified to derive a relationship between the Néel temperature and the parameter u. The modified Bloch equation gives a closer agreement with the experimental results than the Weisz equation.