我国几个矿区叶蜡石X射线粉晶衍射研究   总被引：4，自引：0，他引：4  

李文瑛 《矿物学报》1989,9(4):378-382

对我国几个主要类型叶蜡石矿的叶蜡石做了X射线粉晶衍射研究。从大量实验结果发现,所研究叶蜡石存在单斜晶系和三斜晶系两种多型。单斜晶系(2M);空间群G_(2h)~6-C2/c,a=5.175A,b=8.902A,c=18.673A,β=100.1°,Z=4;三斜晶系(1Tc):空间群P_c,a=5.162A,b=8.965A,c=9.346A,a=91.2°,β=99.96°,γ=89.91°,Z=2。  相似文献   

A garnet population in Yellowknife schist, Canada   总被引：6，自引：0，他引：6  

R. KRETZ 《Journal of Metamorphic Geology》1993,11(1):101-120

Abstract Data are presented on a garnet population in a specimen of garnet-biotite-plagioclase-quartz schist from the cordierite zone of an Archaean thermal dome in the Southern Slave Province of the Canadian Shield. Garnet crystals are bounded by planar dodecahedral faces and by trapezohedral faces which on the 10-μm scale are corrugated. Crystal distribution, as revealed by dissection of a small cubic volume of rock, is random. The size distribution is normal, with a mean diameter of 0.81 mm and a standard deviation of 0.32 mm. In the largest crystal of the population (mean radius 0.83 mm), [Mn] = 100 Mn/(Fe + Mg + Mn + Ca) decreases from 14.5 at the centre to 7.5 and then increases in the outer margin to 8.5; [Fe] increases continuously from 67 at the centre to 77 at the surface; [Mg] increases from 12.5 to 13.5 and then falls sharply to 11; [Ca] remains unchanged at 4.0 and then drops to 3.3. Progressively smaller crystals have progressively lower [Mn] and higher [Fe] concentrations at their centres, while all crystals have the same margin composition. Growth vectors extending from given concentration contours to crystal surfaces are of equal length regardless of the size of the crystal in which the vector is located. A garnet-forming model is presented in which reaction was initiated by a rise in temperature. Nucleation sites were randomly selected. The nucleation rate increased with time and then declined. Crystal faces advanced at a constant linear rate, which implies an increase in volume proportional to surface area. Initially, the composition of garnet deposited on crystal surfaces was determined by van Laar equations of equilibrium, which demanded the withdrawal of Mn and Fe from within chlorite crystals. This transfer reaction was then accompanied by an ion exchange reaction which moved Mn and Fe to garnet surfaces from biotite, in exchange for Mg. The exchange reaction provides an explanation for the high overall concentration of Mn and Fe in garnet and for the observed Mn and Mg reversals in the margins of crystals. The increase of garnet volume in the garnet population is found to be parabolic, i.e. Vαα⁵.  相似文献   

新疆阿尔泰花岗岩源区混合-结晶分异复合过程的微量元素效应     

刘伟  刘丛强 《大地构造与成矿学》1993,17(4):335-344

根据微量元素e1、e2、e3总分配系数的相对大小,源区混合-结晶分异复合过程在它们的比值-比值相关图上造成三种综合效应。新疆阿尔泰花岗岩微量元素的比值-比值相关图清晰地反映了三种效应,暗示着源区混合-结晶分异复合过程。源区混合机制可能为沉积物质在沉积盆地里的掺合。混合端员可能为:1)成熟度差异悬殊的陆源碎屑物质;2)陆源碎屑与基性火山物质。  相似文献   

湘南多金属矿床方解石形态及表面微形貌的研究     

李荣清 《湖南地质》1994,13(1):25-28

对湘南多金属成矿区方解石的研究表明，产于钨矿床中的方解石以层状晶体发育为特征，晶体形态主要为｛０００１｝和｛０１２｝＋｛１０１０｝，晶体表面具有菱形生长阶梯；产于铅锌矿床中的方解石一般不出现层解石，晶体形态主要为｛２１３１｝，｛０１１２｝＋｛１０１０｝和｛０００１｝＋｛１０１０｝＋｛０１１２｝，晶体表面平行纹发育；远矿正常灰岩内方解石晶体形态主要为｛４０４１｝。  相似文献   

内蒙古苏尼特左旗地区堆晶角闪辉长岩的发现及地质意义   总被引：6，自引：0，他引：6  

李玉文  邓晋福 《现代地质》1995,9(2):212-219

通过详细的野外工作和室内研究，发现苏尼特左旗附近较广泛地分布有一种主要由角闪石和外长石组成的堆晶岩，其化学成分属基性岩范畴，可定名为堆晶角闪辉长岩。这类岩体具清楚的层状构造、堆晶结构．岩石化学成分、稀土元素、结构和构造等特征均表明，该类岩石是由富水的拉斑玄武岩浆经分离结晶作用形成的，是造山带火成岩组合中的一个主要组成部分，形成于造山构造岩浆旋回的早期阶段。  相似文献   

新疆萨尔布拉克金矿找矿矿物学标型特征研究   总被引：2，自引：1，他引：2  

吕瑞英 《地球科学》1990,15(6):657-665

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钇易解石族的端员—钛钇易解石的发现     

陈德潜  尹道玲 《地质论评》1994,40(1):82-86

本矿物为新发现的钇易解石族的端员矿物－钛钇易解石，产于江西省龙南县足洞燕山期中粒白云母花岗岩及其风化壳中。矿物属斜方晶系，常呈板状或短柱状，为天然晶质体，浅黄色，粒度为０．０７５ｍｍ，硬度４．７，比重４．７３，二轴正晶，Ｎｇ＝２．２４８，Ｎｍ＝２．２１２，Ｎｐ＝２．１９４，Ｎｇ－Ｎｐ＝０．０５４，２Ｖ＝７０°。空间群为Ｄ＾１６２ｈ－Ｐｍｎｂ，ａ０＝０．７５０ｎｍ，ｂ０＝１．０９２ｎｍ，Ｃ０＝０．５  相似文献   

Crystal structure refinement of hendricksite,A Zn- and Mn-rich trioctahedral potassium mica: A contribution to the crystal chemistry of zinc-bearing minerals     

Dr. J. -L. Robert  Dr. M. Gaspérin 《Mineralogy and Petrology》1985,34(1):1-14

Summary The crystal structure of hendricksite, a trioctahedral mica of biotite type, characterized by high Zn²⁺ and Mn²⁺ contents has been refined by least square methods. The structural formula is: (K_0.89Na_0.10Ba_0.04)(Mg_1.57Zn_0.54Mn _0.40 ²⁺ Fe _0.25 ²⁺ Al_0.07Ti_0.07Cr_0.01)(Si_2.92Al_1.08)O₁₀ (OH)₂. The space group isC2/m and the cell parameters are:a=5.340(2) Å,b=9.524(2) Å,c=10.235(3) Å, =100.07(2)^o, the cell volume isV=497.98 ų. The final unweightedR=0.072. Average cation-anion distances in polyhedra are: T–O=1.659 Å, M(1)–O=2.093 Å, M(2)–O=2.088 Å, A–O_long=3.316 Å and A–O_short=3.004 Å; A is the alkaline cation. The rotation angle of tetrahedra is =6.7°. The analysis of electron densities, of the dimensions and distorsions of polyhedra shows that Zn²⁺ is exclusively in octahedral sites; there is no order between six-fold coordinated cations. A comparison between the structural features of hendricksite and those of the two main end-members of biotites, phlogopite and annite, is presented.The effect of the strong covalence of Zn–O bonds is particularly visible on the dimensions and orientations of the thermal ellipsoids of octahedral sites M(1) and M(2) which contain zinc. In all the published structures of trioctahedral micas, the ellipsoids of cationic sites are uniaxial positive, elongated parallel toc ^*. In hendricksite, this is observed only for the two zinc-free sites (T and A; in the octahedra M(1) and M(2), which contain zinc, the ellipsoids are approximately uniaxial negative, flattened parallel toa, which is a unique situation.Zinc which habitually favours the tetrahedral coordinations with oxygen, enters the octahedra only, i.e. the chemically anisotropic sites, in hendricksite. The strong polarizability of Zn²⁺ is proposed to explain this behaviour.An examination of the behaviour of Zn²⁺ in other compounds shows that this situation is general, zinc favours chemically anisotropic sites and specially those adjacent to OH or H₂O.

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Affinement de la structure cristalline de la hendricksite, mica trioctaédrique potassique riche en Zn et Mn; une contribution à la connaissance cristallochimique des minéraux zincifères

Résumé On a affiné par moindres carrés la structure de la hendricksite, mica trioctaédrique de type biotite, caractérisé par une teneur élevée en Zn²⁺ et Mn²⁺. La formule structurale de ce mica est: (K_0m89Na_0,10Ba_0,04)(Mg_1,57Zn_0,54Mn _0,40 ²⁺ Fe _0,25 ²⁺ Al_0,07Ti_0,07Cr_0,01)(Si_2,92Al_1,08)O₁₀(OH)₂. Le groupe spatial estC2/m et les paramètres de la maille:a=5,340(2) Å,b=9,254(2) Å,c=10,235(3) Å, =100,07(2)°; le volume de la maille estV=497,98 ų. Le résidu final non-pondéré estR=0,072. Les distances cation-anion moyennes dans les polyèdres sont les suivantes: T–O=1,659 Å, M(1)–O=2,093 Å, M(2)–O=2,088 Å, A–O_long=3,316 Å et A–O_court=3,004 Å où A désigne le cation alcalin. L'angle de rotation tétraédrique, =6,7°, est très semblable à celui de la phlogopite. L'analyse des densités électroniques, des dimensions et distorsions des polyèdres montre que Zn²⁺ est exclusivement en coordinance octaédrique et qu'il n'y a pas d'ordre entre les cations hexacoordonnés. On présente une comparaison des caractères structuraux de la hendricksite avec ceux des deux principaux pôles des biotites, la phlogopite et l'annite.L'effet de la forte covalence de la liaison Zn–O est particulièrement visible sur les dimensions et orientations des ellipsoides d'agitation thermique des deux sites octaédriques, sites zincifères. Dans toutes les structures de micas trioctaédriques publiées, les ellipsoides des sites cationiques sont uniaxes positifs, allongés parallèlement àc ^*, ce qui s' observe effectivement dans les deux sites non-zincifères (T et A) de la hendricksite, par contre, dans les octaèdres M(1) et M(2), qui contiennent le zinc, les ellipsoides sont approximativement uniaxes négatifs, applatis parallèlement àa, ce qui est une situation unique.Le zinc, qui se fixe généralement en sites tétraédriques dans les structures de type oxyde, occupe les sites octaédriques, c'est-à-dire les sites chimiquement anisotropes dans la hendricksite. La forte polarisabilité de Zn²⁺ est proposée pour expliquer ce comportement.Un examen du comportement de Zn²⁺ dans d'autres phases montre que cette situation est tout à fait générale, le zinc privilégiant les sites chimiquement anisotropes et en particulier ceux adjacents à OH où H₂O.

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兴安石的晶体结构     

西门露露  彭志忠 《矿物学报》1985,(4)

兴安石是我国新发现的一种富含稀土、铍的硅酸盐新矿物,其理想的化学式为(Y,Ce)BeSiO_4(OH)。该矿物属于单斜晶系,利用四圆单晶衍射仪收集强度数据,测得α=4.7681±0.00263,b=7.6757±0.00686,c=9.9301±0.00639;α=90°,β=90.17°±0.053°,γ=90°;空间群为P2_1/c;Z=4。利用直接法及电子密度函数法测定了晶体结构,经最小二乘修正,最后的偏离因子R=0.086。 结构测定结果证实兴安石具有硅硼钙石的结构类型,与羟磷铍钙石,硅铍钇矿等均属同构似型矿物。  相似文献   

衍射指标h和k的互换问题     

张冠英 《矿物学报》1986,(2)

通过衍射线指标和面网指标的联系讨论了晶体的对称性对衍射指标h和k互换的影响。在下列情况下衍射指标h和k是不能互换的:在低级晶族;在四方晶系C_(4h)—4/m劳厄点群,六方品系C_(6h)—6/m劳厄点群和立方晶系T_h—m3劳厄点群对于hko和kkl型衍射;在三方晶系选取六方晶胞的情况下,在C_(3i)—3劳厄点群对于hol,okl,hko和hkl型衍射,在D_(3d)—3m劳厄点群对于holokl和hkl型衍射,以及在菱面体点阵除非h和k都是三的倍数。  相似文献