尼日利亚石—塔菲石—黑铝镁铁矿及相关系列矿物的晶体结构构筑原理

从氧原子最紧密堆积以及阳离子充填四面体和八面体空隙原理出发 ,以简单氧化物矿物最紧密堆积结构类型金绿宝石、尖晶石、铁钒矿为基础 ,深入讨论了复杂氧化物矿物最紧密堆积结构类型彭志忠石、尼日利亚石、塔菲石、黑铝镁铁 (钛 )矿等晶体结构构筑原理。以O表示全部为阳离子八面体配位的层 ;以T层表示阳离子八面体配位与阳离子四面体配位的混合层 ,其中T1表示阳离子八面体配位与一种方向阳离子四面体配位的混合层 ,T2 表示阳离子八面体配位与两种方向阳离子四面体配位的混合层。这类矿物晶体结构可用O、T1、T2 堆积方式表征 ,O层与T层交替排列。如 :彭志忠石 ( 6H)的晶体结构表示为…OT2 OT1OT1… ,塔菲石 ( 8H)的晶体结构表示为…OT2 OT1OT2 OT1… ,尼日利亚石 ( 2 4R)的晶体结构表示为…OT1OT2 OT2 OT1…× 3 ,等等 ;它们的晶体结构中既有尖晶石的…OT2 OT2 …晶体结构单位 ,又有铁钒矿的…OT1OT1…晶体结构单位。     

层状硅酸盐矿物晶体结构的多体性组装模式与构筑原理

将层状硅酸盐矿物晶体结构中属性不同的二维结构单元体看成是不同的结晶学模块,研究了一般层状硅酸盐矿物和间层矿物的多体性组装模式和构筑原理。结果表明,不同二维结构单元体(包括硅氧四面体片、八面体片、层间域(物))的构筑基本符合球体紧密堆积原理,紧密堆积层平行{0001};四面体片与八面体片构筑TO和TOT结构层时采取多种机制消除二者在二维尺寸上的差异;两种模式的结构层与不同类型的层间物(域)组装形成六种组装模式的晶层;并通过二维结构单元体的组合规律的分析,计算出可能存在的28种TOT型间层结构,它们分属于6种间层结构多体性组装模式;间层结构中,结构层对于八面体片是不对称的,并在属性上表现出极性特征;间层矿物的晶层类型可用6种多体性组装模式加以表达。层状硅酸盐矿物结构的多体性分析与组装模式的研究,对于矿物晶体化学研究是非常重要的。     

DFT study of the cation arrangements in the octahedral and tetrahedral sheets of dioctahedral 2:1 phyllosilicates

Quantum mechanical calculations based on the density functional theory (DFT) are used to study the crystal structures of dioctahedral 2:1 phyllosilicates. The isomorphous cation substitution is investigated by exploring different substitutions of octahedral Al³⁺ by Mg²⁺ or Fe³⁺, tetrahedral substitution of Si⁴⁺ by Al³⁺, and different interlayer cations (IC) (Na⁺, K⁺, Ca²⁺, and Mg²⁺). Samples with different kinds of layer charges are studied: only tetrahedrally charged, only octahedrally charged, or mixed octahedral/tetrahedral charged. The effect of the relative arrangements of these substitutions on the lattice parameters and total energy is studied. The experimental observation of segregation tendency of Fe³⁺ and dispersion tendency of Mg²⁺ in the octahedral sheet is reproduced and explained with reference to the relative energies of the octahedral cation arrangements. These energies are higher than those due to the IC/tetrahedral and IC/octahedral relative arrangements. The tetrahedral and octahedral substitutions that generate charged layers also tend to be dispersed. The octahedral cation exchange potentials change with the IC-charge/ionic radius value.     

How stacking disorder can conceal the actual structure of micas: the case of phengites

The present study deals with how stochastic stackings of tetrahedral/octahedral phengitic sheets bearing diverse cation distributions affect diffraction signals and the structural inferences therefrom derived. The interest for such minerals is dictated by that the stability of phengite polytypes, their cation distributions and P/T conditions of crystallization are related to each other. We focus our attention on layers’ probabilistic sequences that preserve the topology of the polytypes 2M ₁(SG: C2/c) and 3T(SG: P3₁12). Neutron diffraction intensities are modelled by a Monte Carlo approach and then used as artificial experimental data for conventional structure refinements that yield the occupancy factors in the fourfold (Si, Al) and sixfold (Al, Mg) coordination sites of 2M ₁ and 3T. The cation ordering from structure refinement tallies with the one of the “average structure” of a stochastic stacking, but it can significantly differ from those of the individual tetrahedral/octahedral sheets. For instance, sheets having ordered cation arrangements can lead to a stochastic structure which is supposed to bear a fully disordered cation partitioning according to structure refinement. This affects the configuration entropy contributions: the values obtained by conventional refinements can deviate from the correct ones up to 30 %. The analysis of the equivalent reflection intensities brings to light the anomalies hinting at the occurrence of such stacking disorder (using modelled reflections, the mean ratio between standard deviation and average intensity of symmetry equivalent reflections is ideally 0 for perfect crystal structures, but it can amount up to 6 in stochastically disordered phengites). However, taking into account the instrumental uncertainties and the deviations from ideality of actual crystals, such phenomena are very difficult to be detected experimentally.     

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.     

Mg-Cr~(2+)橄揽石、辉石和尖晶石的晶胞参数测定及Cr~(2+)在各晶体结构中的占位

本文用Mg－Cr2+做榄石、辉石、尖晶石的粉晶X射线衍射数据，采取“整体图谱最小二乘Rietveld”方法计算了上述矿物的晶胞参数和摩尔体积，并对Cr2+在各晶体结构中的占位情况进行了研究。结果显示，各矿物的晶胞参数随含Cr2+量的增大而增大。据Vegard定律，推算出各端元组分铬橄榄石（Cr2SiO1）、铬辉石（Cr2SiO2O6）及立方铬尖晶石（Cr3O4）的摩尔体积分别为47．7，68．0，44．9cm3。精化结构参数指示，在橄榄石中，Cr2+随机分配在两个八面体（M1，M2）位置；在辉石中，Cr2+优先选择八面体M2位置；在尖晶石中，Cr2+占置四面体位置。这种晶体内离子分配可从离子半径差别或晶体场稳定能大小得到解释。     

湖南香花岭矽卡岩中锡的矿物学行为与成矿过程

湖南香花岭矽卡岩型锡矿床是南岭地区一个重要的锡多金属矿床,发育有丰富的含锡矿物。在野外和显微镜下观察 基础上,文章利用电子探针技术系统分析了香花岭矽卡岩中含锡矿物的矿物学特征,探讨了锡的成矿过程、成矿流体以及 锡的来源。研究结果表明,香花岭矽卡岩中含锡矿物由锡矿物（锡石、尼日利亚石、孟宪民石等）和富锡矿物（韭闪石、 尖晶石、葡萄石、塔菲石等）组成。锡的成矿有三个阶段：矽卡岩早阶段,Sn进入尖晶石、韭闪石等造岩矿物中,形成富 锡矿物;氧化物阶段,锡矿物如锡石、尼日利亚石、孟宪民石等逐渐晶出;晚期热液阶段,早期含锡矿物热液蚀变原位析 出锡石,或富Sn热液交代早期矿物形成了富锡环边。矽卡岩中成矿流体富含F,CO2,Li等挥发组分,控制了Sn的富集、迁 移、结晶等过程。香花岭矽卡岩中Sn根本上来源于地层,锡的成矿过程反映了Sn在地壳中的地球化学循环过程。     

Crystal-chemistry of natural and heated aluminous orthopyroxenes

X-ray single crystal diffraction data of natural and heated Al-rich orthopyroxenes were used to study the cation ordering and the geometrical changes induced by Si+R ²⁺=Al^IV+R ³⁺ substitution. The calculated site populations and the observed bond distances in tetrahedral and octahedral sites suggest a total ordering of Al^IV in the TB tetrahedron and of R ³⁺ cations in the M1 octahedron, even in samples heated at 1000° C. The mismatch between the tetrahedral and octahedral layers along the c axis seems to play a crucial role in determining the limits of Si/Al^IV substitution.     

我国矿物晶体结构与晶体化学研究进展及新成果(2000-2019)

矿物的晶体结构与晶体化学是矿物学的重要基础研究领域之一,21世纪以来,随着国家对地勘行业的重视,以及平面探测技术单晶衍射仪、微区、微量衍射等实验技术的应用与计算机软硬件能力的提高,我国矿物晶体结构与晶体化学研究得到飞速发展.矿物晶体结构测定与研究是伴随着新矿物的发现而发展的,新矿物的发现是矿物晶体结构研究的基石,又为新...     

Potassium coordination in trioctahedral micas investigated by K-edge XANES spectroscopy

Summary Fine-grained homogeneous powder samples of thirteen trioctahedral micas, mostly intermediate members of the phlogopite – annite solid solution series, and samples close to the phlogopite, fluor-phlogopite and tetra-ferriphlogopite end members have been examined at the potassium K-edge by X-ray absorption fine structure spectroscopy. The interlayer K⁺ cation is in a coordination that is certainly lower than 12, in contrast to what is expected from the ideal hexagonal symmetry model of the mica structure, and approaches – but it does not reach – coordination 6, as it should be when the effective ligands are the three nearest outer bridging oxygens of two facing upper and lower tetrahedral sheets. The observed range of coordinations implies that only some of the three inner bridging oxygen atoms in each sheet are involved, thus leading to 6±(1 … 6) effective configurations depending on the composition of the individual mica terms. The effective coordination number was found to vary continuously with composition from 11 to 7 and to be related to the tetrahedral rotation angle (α) according to two different linear relationships for the phlogopite – annite series (Fe²⁺Mg₋₁ exchange vector, involving the octahedral sheet only) and the phlogopite – tetra-ferriphlogopite series (Fe³⁺Al₋₁ vector, involving the tetrahedral sheet), respectively. Substitutions affecting either the A cation in the interlayer or the X anion in the octahedral sheet also affect the observed trends. In particular, the latter substitution effect is best seen in two near end member phlogopites, where the fluorine to hydroxyl substitution (F⁻ (OH)⁻₋₁ exchange vector), which greatly changes the α tetrahedral rotation angle is, reflected in the experimental K XANES spectra by modifying not only the energy but also the intensities of most multiple scattering features.     

Clay Minerals in an Active Hydrothermal Field at Iheya‐North‐Knoll,Okinawa Trough

Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.     

柱撑粘土矿物材料的晶体结构和晶体化学特征

以铝基柱撑粘土矿物和钛基柱撑粘土矿物为例，讨论了柱撑粘土矿物材料的晶体结构和晶体化学特点，Al多核笼状阳离子基团的结构形式为1：12Keggin型离子，Ti多核笼状阳离子基团的结构形式为2：19Dawson型离子，两类笼状阳离子的直径均在1nm左右，前者的高度约为0．9nm，后者的高度约为1．4nm，经与粘土矿物层间阳离子交换后，择位固定在粘土矿物层间，由于多核笼状阳离子与粘土矿物硅氧四面体之间形成了较强的化学键，其具有不可交换性，铝基柱撑粘土和钛基柱撑粘土的层间孔道分别为1．2nm*1.2nm*1.2nm，和0.52nm*0.52nm*1.60nm。柱粘土矿物材料有很好的化学稳定性和耐热性，且又有一定的层间化学活性，可用于催化剂载体，由于它又具有选择性吸附能力，有望制造成新一代环保材料。     

Theoretical modelling of cis -vacant and trans -vacant configurations in the octahedral sheet of illites and smectites

 The cis-vacant configurations of smectites and illites have been studied theoretically by using transferable empirical interatomic potentials. A wide range of compositions of octahedral and tetrahedral cation and interlayer charge has been considered. All results have been compared with the trans-vacant configurations in each sample. The calculated values reproduce the differences in the lattice parameters between the cis- and trans-vacant configurations of experimental studies. Taking into account the cis-/trans-vacant proportion, the calculated structures agree with experiment for the main structural features of the crystal lattice. The effect of the cation substitution in the octahedral and tetrahedral sheets on the cell parameters has been also studied, finding good linear relationships. The calculated cation substitution effects are consistent with experimental results. Although the energy difference between the cis- and trans-vacant configurations is small, the cis-vacant is more stable when the composition of clays is more smectitic, like the experimental behaviour. Similar trends of the cation substitution effect on the cis-/trans-vacant proportion to the experimental results are found. The structure of the hydroxy groups has also been analysed. The OH bond length, the orientation of the O–H bond with respect to the (001) plane and the non-bonding H...O distances have been studied. Received: 4 September 2000 / Accepted: 29 January 2001     

含铬蒙脱石中铬离子占位位置研究

采用提纯后的蒙脱石在不同浓度硫酸铬溶液中进行交换吸附制备了含铬蒙脱石,并利用包括粉末X射线衍射术 （XRD）、电子自旋共振谱术（ESR） 和傅里叶变换红外吸收光谱术（FTIR） 等分析测试手段对铬在蒙脱石中的吸附位置进 行了探索研究。研究结果显示铬离子不仅置换了层间域中的Ca2+,K+和Na+等,而且置换了位于八面体位的Mn2+ 和少量 Al3+,并较大量的进入硅氧四面体的六边形孔洞、甚至有可能置换极少量的四面体位的Al3+和Fe3+等。此外,根据X射线衍 射分析可知,在0.2 mol/L硫酸铬溶液中充分交换吸附后的蒙脱石存在两层水型和单层水型两种含铬蒙脱石,其水合阳离子 分别为[Cr(H2O)6]3+和[Cr(H2O)3O3]3+,当吸附量增大至一定程度后水合铬离子借助TOT结构片的硅氧四面体的底氧形成配位多 面体。     

Modeling of dioctahedral 2:1 phyllosilicates by means of transferable empirical potentials

 Dioctahedral 2:1 phyllosilicates with different interlayer charge have been studied theoretically by using transferable empirical interatomic potentials. The crystal structures of pyrophyllite, muscovite, margarite, beidellite, montmorillonite, and different smectites and illites have been simulated. The interatomic potentials were able to reproduce the experimental structure of phyllosilicates with high, medium and low interlayer charge. The calculated structures are in agreement with experiment for the main structural features of the crystal lattice. The effect of the cation substitution in the octahedral and tetrahedral sheets on the structural features has been also studied. Good linear relationships have been found, and the calculated effects are consistent with experimental results. Some unknown structural features of the crystal structures of clays are predicted in this work. Received: 8 March 2000 / Accepted: 19 September 2000     

Crystal structural features of the olivine → spinel transition

Comparisons of structural features of olivine (α phase), spinel (γ phase), and the modified spinel (β phase) lead to predictions of possible mechanisms for the olivine → spinel transitions. In the olivine structure, rigid tetrahedral edges and shared octahedral edges form columns of corner-sharing trigonal dipyramids parallel to the a axis. These rigid columns are separated by weaker, unshared octahedral edges which may be stretched to reduce cation-cation repulsion. As a result, olivine has a relatively loose structure and is stable at low pressure. At elevated pressure, olivine transforms to the more compact spinel structure, in which the rigid tetrahedral edges and shared octahedral edges form a three dimensional network instead of aligned columns. These structural differences explain how compressibility and thermal expansion may be taken up mainly by octahedral sites in olivine, but are evenly distributed over both octahedral and tetrahedral sites in spinel. Because the closest packings of oxygens and interstitial cation distributions differ between olivine (h.c.p.) and spinel (c.c.p.), the olivine structure may have to disintegrate during its transformation to spinel, so that the olivine → spinel transition involves processes of nucleation and growth. The migration of atoms across the olivine-spinel interface is thus a complicated process of random walk without a definite path. In the β phase → spinel transition, however, the diffusion of cations may follow a definite path in restricted regions because oxygen closest packings and cation distributions are similar in the two structures. If the oxygen packing remains intact during the β → γ transition, the transformation will be an intracrystalline process leading to domain structure in the spinel product.     

Hydrogen bonding and vibrational properties of hydroxy groups in the crystal lattice of dioctahedral clay minerals by means of first principles calculations

The hydroxy groups of the crystal lattice of dioctahedral 2:1 phyllosilicates were investigated by means of quantum-mechanical calculation. The standard Kohn-Sham self-consistent density functional theory (DFT) method was applied using the generalized gradient approximation (GGA) with numerical atomic orbitals and double-zeta polarized functions as basis set. Isomorphous cation substitution of different cations in the octahedral and tetrahedral sheet was included along with several interlayer cations reproducing experimental crystal lattice parameters. The effect of these substitutions and the interlayer charge on the hydroxyl group properties was also studied. These structures represent different cation pairs among Al³⁺, Fe³⁺ and Mg²⁺ in the octahedral sheet of clays joined to OH groups. The geometrical disposition of the OH bond in the crystal lattice and the hydrogen bonds and other electrostatic interactions of this group were analyzed. The frequencies of different vibrational modes of the OH group [(OH), (OH) and (OH)] were calculated and compared with experimental data, finding a good agreement. These frequencies depend significantly on the nature of cations which are joined with, and the electrostatic interactions with, the interlayer cations. Besides, hydrogen-bonding interactions with tetrahedral oxygens are important for the vibrational properties of the OH groups; however, also the electrostatic interactions of these OH groups with the rest of tetrahedral oxygens within the tetrahedral cavity should be taken into account. The cation substitution effect on the vibration modes of the OH groups was analyzed reproducing the experimental behaviour.Dr. V. Botella passed away last February     

成矿元素富集机制的量子地球化学研究——以攀枝花钒钛磁铁矿矿床为例

攀枝花钒钛磁铁矿矿床为富集钒、钛、铁等过渡元素的典型岩浆矿床。文章运用量子地球化学的理论和方法研究该矿床的元素组合、分配及变化特征 ,并用量子力学理论的abini tioHartree Fock分子轨道法对钛磁铁矿和钛铁矿晶体结构进行了模拟计算。结果表明 :源于地幔的原始岩浆富集成矿元素 ;在其结晶过程中 ,V ,Ti,Fe等成矿元素再次富集于钛磁铁矿和钛铁矿中而形成矿床 ,这种再富集受晶体结构择位能控制。     

Ordered mixed-layer structures in the Mighei carbonaceous chondrite matrix

High resolution transmission electron microscopy of the Mighei carbonaceous chondrite matrix has revealed the presence of a new mixed layer structure material. This mixed-layer material consists of an ordered arrangement of serpentine-type (S) and brucite-type (B) layers in the sequence … SBBSBB. … Electron diffraction and imaging techniques show that the basal periodicity is ~ 17 Å. Discrete crystals of SBB-type material are typically curved, of small size (<1 μm) and show structural variations similar to the serpentine group minerals. Mixed-layer material also occurs in association with planar serpentine. Characteristics of SBB-type material are not consistent with known terrestrial mixed-layer clay minerals. Evidence for formation by a condensation event or by subsequent alteration of preexisting material is not yet apparent.     

AgS_2-Cu_2S-PbS-Bi_2S_3四元体系相关系研究(Ⅱ):铜银铅铋硫盐矿物结晶化学及分类

对Ag_2S-Cu_2S-PbS-Bi_2S_3四元体系内铋硫盐矿物的类质同象取代类型的研究表明,它共有四种:配对取代Ag(Cu)+Bi=2Pb,简单取代Ag=Cu,Bi(Pb)=Cu和Cu原子填隙(以平衡Bi或Pb为Cu取代时电价差)。研究还给出了体系内10个重要固溶体的成分及结晶参数之间的关系。对这些固溶体及铜、银、铅铋硫盐矿物结构特征、共生和共生长关系研究表明,它们可以分成四个系列:块硫铋银矿、硫铋铅矿、辉铋矿-针硫铋铅矿、贺硫铋铜矿。