铁橄榄石-莱河矿组矿物的热力学研究

自从莱河矿作为一个富含Fe~(3+)的正硅酸盐新矿物被研究以来,已有可能将铁橄榄石-莱河矿,看成一个新的矿物系列。在这个系列中已报道的有铁橄榄石、变铁铁橄榄石,高铁铁橄榄石和莱河矿。 此组矿物除铁橄榄石外,热力学性质目前还没有实验资料。为此本文运用了一些近似计算的方法对该组矿物(重点是莱河矿)的热力学参数作了估算,对莱河矿的可能成因和生成条件提出了一些初步看法。     

莱河矿的超结构和低温穆斯堡尔谱的对比研究

本文进行了莱河矿3C超结构和4.2K穆斯堡尔谱的对比研究。研究表明。莱河矿的非等效位置M2A+M2C,M2B,M1B,M1A和VB能够分别与Kan等(1985)测定的莱河矿穆斯堡尔谱的吸收双峰A,B,C,D和E对应,不仅解决了超结构位置和吸收双峰之间的对应,而且圆满解释了吸收双峰A:B和C:D的强度比为2:1的关系。另外,还利用莱河矿超结构的资料讨论了莱河矿的反铁磁性内部作用。     

莱河矿中阳离子的分布

在100—688K之间测量了河北莱河矿的穆斯堡尔谱。高温穆斯堡尔谱表明,莱河矿只显示一个Fe~(2+)双峰。没有测出铁榄橄石的存在。如果将莱河矿冷却到室温以下,则在240K首先出现磁分裂的谱线。从莱河矿的Fe~(2+)和Fe~(3+)双峰的面积比和化学成分能估算Fe~(2+)和Fe~(3+)的占位以及空位在M_1和M_2上的分布:对M_1来说为0.65Fe~(2+)+0.35□;对M_2来说为0.90Fe~(3+)+0.1□。Fe~(2+)和Fe~(3+)的同质异能位移随温度的变化率分别为-9.8×10~(-4)mm/s·K和-5.7×10~(-4)mm/s·K,计算了四极分裂与温度的相关性     

莱河矿——一个铁硅酸盐新矿物

莱河矿是一个铁硅酸盐新矿物，它产于我国东北莱河村的一个变质铁矿中。     

莱河矿的晶体结构

莱河矿是一个含高铁的硅酸盐新矿物。该矿物的矿物学研究结果见文献[1]。实验用的标本取自我国东北莱河村的一变质铁矿中。     

莱河矿的高分辨电镜研究

用高分辨电子显微术研究了莱河矿的晶体结构,并讨论了显微片层结构特征和产生原因。     

莱河矿超结构的高分辨电镜研究

用高分辨电子显微术和光学衍射技术研究了莱河矿的三种超结构类型——3C_1,2C,3C_2。超结构的存在是由于Fe~(2+)空位的不同有序分布产生的。通过观察象与模拟象的比较,建立了相应的结构模型。     

高铁铁橄榄石热处理产物的研究

1976年以来,先后在我国辽宁省莱河及河北省迁西县发现了高铁铁橄榄石,它们的化学通式为Fe~(3 )Fe_2~(3 )(SiO_4)_2;产在辽宁省莱河的高铁铁橄榄石曾被命名为莱河矿。作者曾用穆斯鲍尔效应研究过这种矿物。本文的目的是用X射线、红外光谱及穆斯鲍尔谱研究采自河北省的高铁铁橄榄石的热处理产物,探讨它在氧化和还原条件下的变化,这对阐明该矿物的成因和演化将是有益的。 河北省高铁铁橄榄石产在一种特殊的英榴易溶岩中,它与石英、石榴石、易溶石、磁铁矿和石墨共生,在光片和薄片中可以看到它交代易溶石,而被磁铁矿切穿。石榴石又往往包裹上述矿物。本研究所用的高铁铁橄榄石的化学成分为:SiO_231.96,Fe_2O_335.31,Al_2O_3     

莱河矿(Fe0.52+Fe1.03+SiO4)的超结构

莱河矿于1976年在中国辽宁省的磁铁矿床中首次被发现,许多人对它进行过研究。该矿物为黑色、不透明,化学式为Fe_0.58²⁺Fe_1.0³⁺Mg_0.03Si_0.96O₄,虽然它的晶体结构近似于橄榄石,但已确定为单斜晶系,空间群为P2₁/b。本文作者利用X射线、电子探针、高分解能透过电子显微镜对该矿物进行了系统的研究,发现它具有假双晶、超结构和显微条纹结构。     

小莱河麻粒岩相铁建造的矿物组合—变质过程p、T变化的探讨

小莱河太古宙麻粒岩相铁建造的矿物组合有：①斜方辉石（Fs87）＋钙铁辉石＋石英＋磁铁矿±莱河矿；②铁闪石＋铁浅闪石质角闪石＋石英＋磁铁矿＋碳酸盐±Fe－镁川石（云辉闪石）。辉石的出溶显示了它形成的不同阶段：片晶发育的OpxⅡ－CpxⅡ是最后稳定产物，计算的平衡温度是742℃，按相图获得的压力是7×108～7．8×108Pa；钙铁辉石中“001”片晶是易变辉石片晶转变的，Opx－Cpx－Pig（片晶）阶段据相图推测可能形成于近820℃，8×108Pa的条件下。原始均一相的OpxⅠ－CpxⅠ阶段矿物成分按估算的片晶含量计算，它们的形成温度接近820℃，可能的压力范围是11×108～13×108Pa。由此得到ITD型麻粒岩相p－T－t轨迹。莱河矿无氧化成因的证据，认为它是在麻粒岩相条件下生成的。云辉闪石的Si—O链重复周期是3×，其Fe／（Fe＋Mg）＝0．85，是接近富铁端元的Fe－镁川石，它与闪石一起在640到近700℃条件下交代了辉石。     

The stability of laihunite—A thermodynamic analysis

Laihunite, a mineral of ferric and ferrous iron silicate discovered in China in recent years, occurs in high grade metamorphic BIF coexisting with magnetite, quartz, fayalite, ferrosilite and almandinc. Complete nets based on Schreinemakers bundles and partial nets with maximum closure after the method described by H. W. Day have been constructed by taking into account the existence of this mineral in order to illustrate phase relations for the (n+3) multisystem in the system Fe₂O₃-FeO-SiO₂. Judging from Lindsley’s experimental data on ferrosilite, laihunite-ferrosilite assemblage is expected to be stable at pressures probably higher than 15 kb. Two-pyroxene and garnet-clinopyroxene geothermometers gave the temperatures of formation between 600–700°C. The free energy of laihunite calculated according to Chen’s method and estimated heat capacity power-function coeficients allow oxygen fugacity to be plotted against temperature at different total pressure swith respect to a number of univariant reactions in which laihunite is involved. The logfo ₂-T diagram demonstrates that to a first approximation the stability field of laihunite overlaps the upper part of the magnetite field, but its upper limit is a little beyond the hematite-magnetite equilibrium. The three major requirements for laihunite stability, i.e., an unusual high pressure, a temperature in the order of 600°C–700°C and a relatively higher oxygen fugacity, are mutually exclusive in common geological environment, which may probably account for the rare occurrence of this mineral in nature. For the BIF in which laihunite occurs, the pressure caused by the weight of overlying strata is not high enough to give rise to its formation even in the extreme case of geothermal gradient. So it is suggested that additional tectonic pressure in response to plate activity might have been involved.     

Modification of olivine surface morphology and reactivity by microbial activity during chemical weathering

Prior transmission electron microscope studies showed that the surface geometry of olivine changes dramatically during natural chemical weathering. However, similar morphological evolution has not been reported in laboratory studies of olivine dissolution. In this study, we examined the development of fayalite (Fe₂SiO₄) surface morphology during both abiotic and biotic (using Acidithiobacillus ferrooxidans) laboratory dissolution experiments at an initial pH of 2.0. The fayalite came from Cheyenne Canyon, Colorado (Smithsonian # R 3516) and contains a few percent laihunite (olivine structure with ordered ferric iron and vacancies, ∼Fe_0.8²⁺Fe_0.8³⁺SiO₄). High-resolution field emission low voltage scanning electron microscope (SEM) characterization of all reacted samples showed etch patterns consistent with those reported from naturally reacted olivine. High-resolution transmission electron microscope (HRTEM) data demonstrated pervasive channeling on (001), with channel spacings that range down to < 10 nm. Formation of channels on (001) is probably initiated by preferential removal of cations from olivine M1 sites. Channeling confers at least an order of magnitude increase in surface area. Relict strips of olivine between channels contain laihunite layers that are oriented parallel to channel margins. X-ray diffraction analyses indicated that the relative abundance of laihunite is higher in reacted compared to unreacted samples. This result is consistent with prior studies of naturally weathered olivine that suggest that laihunite is far less readily dissolved than olivine.Samples reacted in the presence of A. ferrooxidans cells that enzymatically oxidized iron, or in solutions where ferric iron was added to simulate biological activity, dissolve at a much slower rate than samples reacted abiotically. We attribute suppression of the olivine dissolution rate to surface adsorption of Fe³⁺. It is probable that ferric iron adsorption is controlled by M2 sites in the underlying olivine structure. If this is coupled with removal of M1 cations during channel formation, then a modified laihunite-like surface will develop (vacancies in laihunite are on M1 sites). Although surface modification might only penetrate a few atomic layers, an inherently unreactive laihunite-like surface structure could explain both the pervasive channeling and the dramatic suppression of the measured dissolution rate.     

Transmission electron microscopy of subsolidus oxidation and weathering of olivine

Olivine crystals in basaltic andesites which crop out in the Abert Rim, south-central Oregon have been studied by high-resolution and analytical transmission electron microscopy. The observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation. The olivine crystals contain rare, dense arrays of coherently intergrown Ti-free magnetite and inclusions of a phase inferred to be amorphous silica. We interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava. The second olivine alteration assemblage contains complex ordered intergrowths on (001) of forsterite-rich olivine and laihunite (distorted olivine structure with Fe³⁺ charge balanced by vacancies). Based on experimental results for laihunite synthesis (Kondoh et al. 1985), these intergrowths probably formed by olivine oxidation between 400 and 800°C. The third episode of alteration involves the destruction of olivine by low-temperature hydrothermal alteration and weathering. Elongate etch-pits and channels in the margins of fresh olivine crystals contain semi-oriented bands of smectite. Olivine weathers to smectite and hematite, and subsequently to arrays of oriented hematite crystals. The textures resemble those reported by Eggleton (1984) and Smith et al. (1987). We find no evidence for a metastable phase intermediate between olivine and smectite (M — Eggleton 1984). The presence of laihunite exerts a strong control on the geometry of olivine weathering. Single laihunite layers and laihunite-forsteritic olivine intergrowths increase the resistance of crystals to weathering. Preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine, rather than where coherency-strain is associated with laihunite-olivine interfaces.     

Domain twinning of Laihunite and refinement of its crystal structure

Domain twinning of laihunite has been investigated based on diffracton phenomena, and its crystal structure has then been refined. Space group with respect to the domain isP2₁/c, and cell parametersa=5.813,b=4,812,c=10.211(A), β=90.87°. Atomic coordinate and bond length have been recalculated. Discussions are made of the Fe²⁺ distribution, lattice distortion, degree of order of laihunite and the relationship of this mineral with fayalite and ferrifayalite. The authors still hold that laih unite should be considered as a new silicate mineral with dominant Fe³⁺ and less amount of Fe²⁺.     

含氧酸盐矿物生成自由能的计算

地质科学近年来发展的一个重要方向是热力学理论和热化学方法的应用。在地质领域内应用热力学理论的基础是矿物及有关化合物的热力学性质(或热化学数据)。     

岩石矿物及粉尘中游离二氧化硅的测定

改进了游离二氧化硅（fSiO2)测定中试样的分解方法，采用硫－磷混酸替代单独使用磷酸分解试样，防止了焦磷酸盐的形成，同时，氟硼酸对fSiO2的溶解率符合测定要求。改进的方法用于标准物质中fSiO2的测定，结果与标准值或磷酸溶矿重量法相符。对于ω(fSiO2)=3.26%的标样10次测定的RSD为2．4％。     

Thermodynamics of phase transitions in the system ice VI-ice VII-water

The paper presents an analysis of experimental results on phase equilibria in the system ice VI-ice VII-water. The mathematical processing of the experimental data makes it possible to further constrain the location of phase transition boundaries between crystalline ices VI and VII and liquid water. Based on the standard thermodynamic properties of H₂O, an equation was derived for the free energy of formation of liquid water in its stability fields. The equations thus obtained were then utilized to calculate the standard thermodynamic properties (free energy, enthalpy, and entropy) of water ice VI and VII and the free energy of their formation at pressures of 6.3–25 kbar.     

链烷烃的热力学性质与分子拓扑指数的关系

定义了一种新的连接性指数^1Y=Σk1/m^2 n^2,研究了链烷烃的标准生成焓、标准熵、标准生成吉布斯自由能等三个热力学性质与碳原子个数N，^1Y之间的定量关系，相关系数为优，其计算值与实验值较为接近，对未参与回归的正癸烷的60个异构体的三个热力学性质进行了计算，计算值与实验值较一致。