A comparison of the dissolution behavior of troilite with other iron(II) sulfides; implications of structure

Further knowledge as to the nature of the structure of a terrestrial sample of troilite, FeS [stoichiometric iron(II) sulfide] is revealed by a combination of XPS studies and dissolution studies in acid. The XPS analysis of a pristine troilite surface (the sample being cleaved under high vacuum) is compared to that of a surface polished in an inert atmosphere and a surface after reaction in deoxygenated acid. Further comparison is made with polished and acid-reacted surfaces of pyrrhotite (Fe_1-xS) and pyrite (FeS₂). The pristine troilite S2p spectrum comprises mainly monosulfide 161.1 eV, within the reported range of monosulfide, together with evidence of an unsatisfied monosulfide surface state arising from S-Fe bond rupture. Small, higher oxidation state sulfur contributions, including a disulfide-like state are also present, which suggest the presence of defects due to some nonstoichiometry. The dissolution studies showed that the troilite, in addition to dissolving in acid as an ionic solid to produce H₂S, also exhibits some oxidation of sulfur in the surface layers. In addition, a study of the dissolution behavior of troilite under the influence of cathodic applied potential supported the existence of a proportion of the sulfur within troilite needing reduction before dissolution forming HS⁻ or H₂S can occur. A significant increase in the dissolution rate was observed with application of −105 mV (SHE), but further stepped decreases in potential to −405 mV and −705 mV resulted in a decreased rate of dissolution, a response typical of an ionic solid. The results of the studies emphasise the viewing of iron(II) sulfides as a continuum. Pyrrhotite has been reported previously to dissolve in acid both oxidatively (like pyrite) and nonoxidatively (like troilite) on the same surface. Dissolution studies using troilite, in Ar-purged acid, indicate that dissolution of this material may not be uniformly nonoxidative. XPS evidence of restructuring of the surface of troilite to pyrrhotite and the surface of pyrrhotite towards a FeS₂ type structure, after exposure to Ar-purged acid, is presented.     

钛钡铬石,钛钾铬石的穆斯堡尔谱研究及晶体化学

本文在结构测定的基础上。应用穆斯堡尔谱技术。确定了钛钡铬石和钛钾铬石中铁离子的价态及结晶学位置。测试结果表明钛钾铬石中Fe的相对含量Fe~(2+)>Fe~(3+),而钛钡铬石中Fe~(2+)相似文献   

Spectroscopic and XRD studies of the air degradation of acid-reacted pyrrhotites

Monoclinic and hexagonal pyrrhotites leached in 1 mol/L HCl and exposed to the air at 100% and ∼10% relative humidity for up to 5 months were studied using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy, Mössbauer spectroscopy, and electron paramagnetic resonance (EPR). The amorphous, nonequilibrium, iron-depleted layer (NL) produced by the leaching amounted to half of the residue mass and was composed of predominantly low-spin ferrous iron and polysulfide anions. Elemental sulfur and goethite were the only crystalline products of the NL decomposition. FTIR spectroscopy and XPS also revealed several sulfoxy species and, at low humidity, a small amount of ferric oxide. Neither alterations of the underlying pyrrhotite nor new iron sulfide phases (pyrite, pyrrhotite, etc.) crystallized from the amorphous NL were found. The NL decomposition was faster in the wet environment than in the dry one, and the oxidation of the NL was much more rapid than that of starting pyrrhotites. The intensity and quadruple split of the Mössbauer signal from the product (an isomer shift of 0.36 mm/s) were found to increase over the aging, indicating that the NL structure becomes more rigid and the singlet Fe(II) gradually converts to Fe(III). X-ray Fe Lα,β emission spectra showed the formation of intermediate, high-spin Fe(II) within the NL oxidized in the humid environment, but not in the dry air. No unpaired electron spins were detected by EPR; lines of paramagnetic Fe³⁺ appeared after the samples were aged in the dry air for 49 d and even later in the humid atmosphere. These phenomena are explained in terms of the formation of defects with negative correlation energy, similar to noncrystalline semiconductor chalcogenides, and of the fast electron exchange between the iron species, respectively. Mechanisms for reactions involved with the weathering of iron sulfides, which take into consideration the NL lattice elasticity, S-S and S-O bonding, oxygen incorporation, and oxidative and spin state of iron, are discussed. It is suggested in particular that the surface layer, strongly enriched in sulfur, as well as elemental sulfur and ferric oxyhydroxides, do not inhibit sulfide oxidation and acid production under weathering conditions, but the partially oxidized, disordered, nonstoichiometric layer may be passive.     

Trace element partitioning in the Morasko meteorite from Poznan, Poland

The nickel–iron meteorite of Morasko shows isolated inclusions of troilite in the bulk mass of a Fe,Ni-alloy. During a segregation of the FeS phase chalcophile trace elements were collected from the melt. The solidification of the Fe,Ni-phase occurred probably later, incorporating thereby mainly siderophile trace elements. To prove this general assumption selected trace elements were determined and reveal in the two phases of the present meteorite a characteristic distribution pattern. The meteorite of Morasko is in close conformity to the iron meteorite group IAB with rounded dark FeS inclusions.     

攀西基性岩中共生的陨硫铁和磁黄铁矿的穆斯堡尔效应研究

使用穆斯堡尔效应研究攀西基性岩中共生的陨硫铁和磁黄铁矿。陨硫铁的分子式为Fe_(1.009)S,晶胞参数a_0=5.96,c_0=11.74,根据Wuensch表示法,可以把它归结为1B,1C型。与陨硫铁共生的磁黄铁矿的分子式为Fe_(0.892)S,属于六方磁黄铁矿。本文确定了共生的陨硫铁和磁黄铁矿的穆斯堡尔参数,它们的谱分别是由一组磁六线谱和三组磁六线谱组成。比较攀西陨硫铁和人工合成陨硫铁及陨石中陨硫铁,可以得出结论,它们之间没有明显差别。     

Solidification History of the Kitdl?t Lens: Immiscible Metal and Sulphide Liquids from a Basaltic Dyke on Disko, Central West Greenland

A unique troilite-iron-cohenite-rich lens was found on a ledgein the sediment-contaminated Kitdlit dyke on Disko. The lensdisplays a mineralogical diversity and extreme liquid evolutionnot previously described from any single magmatic sulphide ormetal liquid system. It was deposited at 1200 ?C and fo2 = 10–¹³as two immiscible liquids–a sulphide liquid and a C-richmetal liquid—which solidified from about 1100? to 300?C as a closed system in a thermal gradient. The lower iron-rich half of the lens formed by crystallizationof iron, cohenite, troilite, schreibersite and w?stite (in thatorder), with trace amounts of the phases found in the upperhalf of the lens. The approximate crystallization order of theupper troilite-rich half of the lens was: iron, cohenite, troilite,chromite, w?stite, fayalite (pseudomorphosed), high-T ‘chalcopyrite’,high-T ‘heazlewoodite’ (beta-(Ni, Fe, Cu, Co)_3+?S₂)and, finally, lead minerals. The latter comprise native lead,galena, altaite (PbTe), shandite (Ni3Pb2S2) and an unidentifiedphase. Additional immiscible liquids were formed during solidification.Oxysulphide liquid (roughly FeO with a minor FeS-component)exsolved from metal and sulphide liquid in equilibrium withiron and cohenite below 1100 ?C. Later, FeO-rich silicate liquid,and Pb-rich liquid with Ni, Cu, S and Te, exsolved from thesulphide liquid. Segregation of oxysulphide and Pb-rich liquidmay occur during core formation in planetoids, and there arethus important cosmochemical implications.     

Magnetic interaction in biotites and oxidised biotites

Mössbauer spectra of biotites (1) and (2) with relative iron concentrations ～1:1·6 and of their oxidation products are recorded at 4 K in zero field and in applied fields up to 5 T. Magnetic susceptibility data are also reported. The results show that Fe III spins are in a ferromagnetic configuration in the c-plane in both biotites. Partial oxidation of biotite (1) leads to a canted ferromagnetic structure, while complete oxidation of biotite (2) yields an antiferromagnetic spin configuration. Nearest-neighbour antiferromagnetic Fe III-O-Fe III, and ferromagnetic Fe III-O-Fe II and Fe II-O-Fe II superexchange can account for the results. For biotites with higher concentrations of iron, Fe II and Fe III seem to be distributed randomly in the triangular lattice. From susceptibility results in biotites dilute in iron, an estimate of the ratio of nearest-neighbour and next-nearest neighbour magnetic interaction in the triangular lattice is derived.     

Chemical and structural characterization of As immobilization by nanoparticles of mackinawite (FeSm)

The mobility and availability of arsenite, As(III), in anoxic environments is largely controlled by adsorption onto iron sulfides and/or precipitation of arsenic in solid phases. The interaction of As(III) with synthetic mackinawite (FeS_m) in pH 5 and 9 suspensions was investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), STEM elemental mapping, high resolution TEM, and X-ray photoelectron spectroscopy (XPS). At pH 5, arsenic sulfide phases precipitate among the FeS_m particles as discrete particles that are an amorphous hydrous phase of arsenic sulfide. The oxidation state of As in the surface layers of the arsenic sulfide precipitates is ‘realgar-like’ based on XPS results showing that > 75% of the As 3d peak area is due to As with oxidation states between 0 and 2+. Discrete, arsenic sulfide precipitates are absent at pH 9, but elemental mapping in STEM-EDX mode shows that arsenic is uniformly distributed on the FeS_m, suggesting that uptake is caused by the sorption of As(III) oxyanions and/or the precipitation of highly dispersed arsenic sulfides on FeS_m. XPS also revealed that the FeS_m that equilibrated without As(III) has a more oxidized surface composition than the sample at pH 9, as indicated by the higher concentration of O ( three times greater than that at pH 9) and the larger fraction of Fe(III) species making up the total Fe (2p_3/2) peak. These findings provide a better understanding of redox processes and phase transitions upon As(III) adsorption on iron sulfide substrates.     

Smyer H-chondrite impact-melt breccia and evidence for sulfur vaporization

Smyer is an H-chondrite impact-melt breccia containing ∼20 vol% 0.5- to 13-mm-thick silicate-rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension. At the interface between some of the melt veins and chondritic clasts, there are troilite-rich regions consisting of unmelted, crushed 0.2- to 140-μm-size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins. Troilite fills every available fracture in the silicates, including some as thin as 0.1 μm. Little metallic Fe-Ni is present in these regions: the FeS/Fe modal ratio ranges from ∼25:1 to ∼500:1, far higher than the eutectic weight ratio of 7.5:1. The texture of these regions indicates that the sulfide formed from a fluid of very low viscosity. The moderately high viscosity (0.2 poise) and large surface tension of liquid FeS, its inability to wet silicate grain surfaces at low oxygen fugacities, and the supereutectic FeS/Fe ratios in the troilite-rich regions indicate that the fluid was a vapor. It seems likely that during the shock event that melted Smyer, many silicates adjacent to the melt veins were crushed. Upon release of shock pressure, some of the troilite evaporated and dissociated. Molecules of S₂ were transported and condensed into fractures and around tiny silicate grains; there, they combined with Fe from small adjacent metallic Fe-Ni grains to form troilite. The Ni content at the edges of some of these metal grains increased significantly; Co from these Ni-rich grains diffused into nearby kamacite. Impact-induced S volatilization may have played a major role in depleting the surface of 433 Eros (and other chondritic asteroids) in S.     

甘肃阳山金矿床含砷黄铁矿及毒砂的XPS研究

阳山金矿是西秦岭地区新发现的超大型金矿.载金矿物中元素的赋存状态是认识成矿机理、评价矿床采选冶过程对环境影响的重要依据.作者运用XPS技术测定了载金矿物含砷黄铁矿和毒砂新鲜断裂面的As3d、Fe2p及S2p的存在形式和相对原子百分含量.结果表明,在含砷黄铁矿表面,超过50%的As以As~(-1)形式存在,约18%～20%的As以As~(3+)形式存在,约30%的As以As~(5+)形式存在.在毒砂表面,超过60%的As以As~(1-)形式存在,约30%的As~(3+)形式存在,其余10%的As主要以As~(3+)形式存在.分析证明As、Fe、S等元素在含砷黄铁矿和毒砂中主要以As`(1-)、Fe~(2+)、S~(1-)形式存在外,As元素可能还以As~(3+)形式存在于含砷黄铁矿及毒砂结构中.     

绿柱石中铁离子的晶格占位及致色作用

绿柱石族宝石颜色丰富,一直是市场上重要的宝石品种。几十年来,国内外学者对不同颜色绿柱石的致色机理及改色工艺开展了广泛的研究。铁离子作为重要的致色过渡金属离子之一,其价态调控是绿柱石改色工艺的关键,所以铁离子的价态、晶格占位和对应的致色作用也一直是绿柱石研究的焦点。铁离子被认为可能存在于绿柱石中的铝氧八面体Al³⁺格位、硅氧四面体Si⁴⁺格位、铍氧四面体Be²⁺格位、结构通道2a或2b位和晶格间隙6g位等位置,是蓝、绿或黄等颜色绿柱石的主要致色元素。本文通过对绿柱石的晶体结构、铁离子的核外电子排布和晶格占位等方面文献资料的梳理及综合分析,认为Fe²⁺和Fe³⁺分别对蓝色和黄色绿柱石的呈色起着主导作用。当Fe²⁺和Fe³⁺处于晶格中不同位置时致色作用的具体差异,仍有待于进一步研究。     

Surface chemistry and structural properties of mackinawite prepared by reaction of sulfide ions with metallic iron

Tetragonal FeS_1−x mackinawite, has been synthesized by reacting metallic iron with a sodium sulfide solution and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mössbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). Based on XRD and TEM analyses, synthetic mackinawite exhibits crystallization and is identical to the natural mineral. Unit cell parameters derived from XRD data are a = b = 0.3670 nm and c = 0.5049 nm. The bulk Fe:S ratio derived from the quantitative dispersive energy analysis is practically 1. XPS analyses, however, showed that mackinawite surface is composed of both Fe(II) and Fe(III) species bound to monosulfide. Accordingly, monosulfide is the dominant S species observed at the surface with lesser amount of polysulfides and elemental sulfur. TMS analysis revealed the presence of both Fe(II) and Fe(III) in the mackinawite structure, thus supporting the XPS analysis. We propose that the iron monosulfide phase synthesized by reacting metallic iron and dissolved sulfide is composed of Fe(II) and S(-II) atoms with the presence of a weathered thin layer covering the bulk material that consists of both Fe(II) and Fe(III) bound to S(-II) atoms and in a less extent of polysulfide and elemental sulfur.     

长江口崇明东滩沉积物地球化学记录及其环境意义

利用2002年在崇明东滩采得的CDS、CDM和CDN三个典型区域沉积物剖面样品,测定了其中的有机碳、活性铁、总磷以及粒度等特征参数,分析了地球化学元素的分布变化特征并对其沉积环境的变化进行了探讨。结果表明崇明东滩沉积物中有机碳的含量较大(0．3％～1．07％),垂向分布上,表层／亚表层含量高且变化复杂,中下层有机碳含量逐渐变小。Fe3 在整个研究区域均是从表层向下逐渐递减的,Fe2 含量逐渐增加。从实验结果判断,所研究区域沉积环境上层以氧化环境为主,呈弱氧化型,中下层以还原环境为主。总磷含量呈现自上而下减少的变化,CDS表现为波浪形变化。分析发现潮滩沉积物各地球化学元素之间不仅相互作用,并且受到沉积物颗粒大小和水动力、物源输入、物理扰动等因素的影响。崇明东滩沉积物氧化还原界面与中、高潮滩划分界大致相当。     

Phosphate bonding configuration on ferrihydrite based on molecular orbital calculations and XANES fingerprinting

Sorption of phosphate by Fe(III)- and Al(III)-(hydr)oxide minerals regulates the mobility of this potential water pollutant in the environment. The objective of this research was to determine the molecular configuration of phosphate bound on ferrihydrite at pH 6 by interpreting P K-edge XANES spectra in terms of bonding mode. XANES and UV-visible absorption spectra for aqueous Fe(III)-PO₄ solutions (Fe/P molar ratio = 0-2.0) provided experimental trends for energies of P(3p)-O(2p) and Fe(3d)-O(2p) antibonding molecular orbitals. Molecular orbitals for Fe(III)-PO₄ or Al(III)-PO₄ complexes in idealized monodentate or bidentate bonding mode were generated by conceptual bonding arguments, and Extended-Hückel molecular orbital computations were used to understand and assign XANES spectral features to bound electronic states. The strong white line at the absorption edge in P K-edge XANES spectra for Fe-PO₄ or Al-PO₄ systems is attributable to an electronic transition from a P 1s atomic orbital into P(3p)-O(2p) or P(3p)-O(2p)-Al(3p) antibonding molecular orbitals, respectively. For Fe-PO₄ systems, a XANES peak at 2-5 eV below the edge was assigned to a P 1s electron transition into Fe(4p)-O(2p) antibonding molecular orbitals. Similarly, a shoulder on the low-energy side of the white line for variscite corresponds to a transition into Al(3p)-O(2p) orbitals. In monodentate-bonded phosphate, Fe-O bonding is optimized and P-O bonding is weakened, and the converse is true of bidentate-bonded phosphate. These differences explained an inverse correlation between energies of P(3p)-O(2p) and Fe(3d)-O(2p) antibonding molecular orbitals consistent with a monodentate-to-bidentate transition in aqueous Fe(III)-PO₄ solutions. The intensity of the XANES pre-edge feature in Fe(III)-bonded systems increased with increasing number of Fe(III)-O-P bonds. Based on the similarity of intensity and splitting of the pre-edge feature for phosphate sorbed on ferrihydrite at 750 mmol/kg at pH 6 and aqueous Fe-PO₄ solutions containing predominantly bidentate complexes, XANES results indicated that phosphate adsorbed on ferrihydrite was predominantly a bidentate-binuclear surface complex.     

Fe2+在零价铁还原去除NO3-中的作用效应

零价铁（Fe0） 被广泛用于地下水中硝酸盐原位与异位修复,但二价铁（Fe2+） 的存在对具有氧化膜的Fe0还原硝酸盐的作用效应仍有待研究。以100 目的未经酸化的颗粒状零价铁作为还原剂,采用室内批试验方法,研究了Fe2+在零价铁还原去除NO3-系统中的作用效应。实验结果表明,Fe2+可显著提高Fe0对于NO3-的去除速率与去除效率,且Fe2+浓度越高,去除速率与效率越高;由于未经酸化的Fe0具有氧化膜,反应初期的NO3-还原速率较慢。Fe2+将零价铁表面的Fe2O3氧化膜转化为Fe3O4,加速电子由Fe0向NO3-的转移,促进NO3-还原。此外,在反应系统中加入Fe3O4,可进一步提高Fe0对于硝酸盐的去除能力,若Fe2+不存在,仅添加Fe3O4,NO3-的去除效率没有提高。     

明溪蓝刚玉的水热溶液改色实验初步研究

明溪蓝刚中Fe主要以Fe^3 形式存在，Fe^3 的d-d电子跃迁和Fe^2 -Ti^4 /Fe^3 -Ti^3 、O^2-Fe^3 间电荷转移是致色的主要因素；浓度差可以作为扩散动力；氢含量的提高可以促进蓝色致因子的形成。采用高温高压水溶液方法对蓝刚玉进行改色处理，可消除刚玉中的杂色调，使颜色向纯蓝色方向变化。     

Oxidation states and speciation of secondary products on pyrite and arsenopyrite reacted with mine waste waters and air

Summary Three morphologically distinct generations of Fe-oxyhydroxides were identified on pyrite surfaces reacted with unsaturated zone waters of a waste rock pile from the CON Mine (Northwest Territories, Canada). The paragenetic sequence includes an early mottled coating and a late massive (featureless) coating, separated by a generation of Fe(III)-oxyhydroxide of crystalline habit. Gypsum and halite precipitation were the last paragenetic events, and indicate intense wetting and drying in the unsaturated zone of the waste rock pile prior to collection.Fe 2p X-ray photoelectron spectra (XPS) of tarnished pyrite surfaces indicate at least two distinct secondary Fe(III)-oxyhydroxide phases, and combined with O 1s spectra, indicate ferrihydrite, goethite, hematite or maghemite. Minor As(IV) and As(III) are incorporated into these coatings.Fresh arsenopyrite surfaces reacted with air for 14 days, 16 months and 25 years develop exceptionally thin oxidized secondary coatings no more than about 50 A thick. XPS Fe 2p, O 1s and As 3d spectra indicate that the overlayer is composed of Fe(III)-hydroxides, arsenate (AsO[OH]3 or FeAsO₄), and reduced arsenic species, including arsenite (As[OH]3 or FeAsO₃). The abundance of reduced arsenic species is explained by diffusion of reduced As (e.g. As) from the unoxidized interior of the mineral to the near-surface where it reacts with oxidants. Continuous supply of reduced As from the bulk, and progressive oxidation of arsenic in the near-surface, result in an effective passivating layer. Whereas these oxidized coatings passivate the surface against airoxidation, aqueous solutions cause extensive leaching of arsenopyrite surfaces beneath the oxidized coatings. Apparently, the coatings offer little protection against leaching by oxidizing aqueous solutions, perhaps because the oxidized overlayer is compromised by dissolution of acidic and ferric arsenite and arsenate salts.

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Oxidationszustand und Spezifikation sekundärer Produkte auf Pyrit und Arsenkies nach Reaktion mit Grubenwässern und Luft

Zusammenfassung Drei morphologisch definierte Generationen von Eisen-Oxyhydroxyden wurden auf den Oberflächen von Pyrit nachgewiesen, der mit Wässern der ungesättigten Zone einer Abraumhalde der CON Mine (Nordwest-Territorium, Kanada) reagiert hat. Die paragenetische Abfolge umfaßt einen frühen fleckigen und einen späten massiven Überzug der durch eine Generation von Fe(III)-Oxyhydroxyden von kristallinem Habitus getrennt werden. Gips und Steinsalz Ausfällung waren die letzten paragenetischen Stadien und weisen auf intensive Befeuchtung und Trocknung in der ungesättigen Zone der Abraumhalden vor der Probennahme hin. Fe2p Röntgenfotoelektronspektren (XPS) von angelaufenen Pyritoberflächen weisen auf zumindest zwei unterscheidbare sekundäre Fe(III)-Oxyhydroxydphasen hin; in Kombination mit O is Spektren zeigen sie auch, daß Ferrihydrit, Goethit, Hämatit oder Maghemit vorliegen. Geringere Mengen von As(IV) und As(111) liegen in diesen Überzügen vor.Frische Arsenkiesoberflächen, die mit Luft für 14 Tage, 16 Monate und 25 Jahre reagiert haben, entwickeln außerordentlich dünne sekundäre Oxydationsfilme, die nicht mehr als 50 A dick sind. XPS, Fe 2p, O l s und As 3d Spektren zeigen, daß diese aus Fe(III)-Hydroxyden, Arsenat (AsO[OH]₃ oder FeAsO₄), und reduzierten Arsenphasen, die Arsenit (As[OH[]₃ oder FeAsO₃) umfassen, bestehen. Die weite Verbreitung von reduzierten Arsenphasen wird durch die Diffusion von reduziertem As (e.g. As°) aus dem nichtoxidierten Teil des Minerals in den Oberflächenbereichen erklärt, dort reagiert es mit Oxidanzien. Kontinuierliche Zufuhr von reduziertem As aus dem Haldenmaterial und progressive Oxidation des Arsens nahe der Oberläche führt zur Bildung einer effektiv passivierenden Schicht. Während diese oxidierten Schichten die Oberfläche gegen Luftoxidation passivieren, verursachen wäßrige Lösungen umfangreiches Leaching von Arsenkiesoberflächen unter den oxidierten Schichten. Offensichtlich bieten diese Schichten geringen Schutz gegen Leaching durch oxidierende wäßrige Lösungen, wahrscheinlich weil die oxidierte Überschicht durch Auflösung von sauren sowie Ferritischen Arsenit- und Arsenatsalzen beschädigt ist.

     

Mineralogy and texture of Fe-Ni sulfides in CI1 chondrites: Clues to the extent of aqueous alteration on the CI1 parent body

To better understand the role of aqueous alteration on the CI1 parent body, we have analyzed the texture, composition and mineral associations of iron nickel sulfides in four of the five known CI1 chondrites.The most commonly-occurring sulfide present in the CI1 chondrites is the iron-deficient Fe,Ni sulfide pyrrhotite ([Fe,Ni]_1−xS), that has a composition close to that of stoichiometric troilite (FeS). Three of the CI1s (Alais, Ivuna and Tonk) also contain pentlandite ([Fe,Ni]₉S₈), although pentlandite is a rare phase in Ivuna. Cubanite (CuFe₂S₃) was found in both Alais and Ivuna in this study, although it has also been reported in Orgueil (MacDougall and Kerridge, 1977). The pyrrhotite grains in all four chondrites form hexagonal, rectangular or irregular shapes, and show no evidence of Ni or Co zoning. The pyrrhotite grains in Orgueil and Ivuna are, in general, smaller, and show more “corrosions,” or “embayments,” than those in Alais or Tonk.We suggest that the precursor sulfide present in the CI1 chondrites was troilite which, during brecciation and oxidation on the parent body at a temperature of 100°C or less, converted the troilite to magnetite and pyrrhotite with pentlandite inclusions. Subsequently, continued alteration on the parent body removed pentlandite—partially from Alais, Tonk and Ivuna, completely from Orgueil—leaving behind pyrrhotite with spaces (“corrosions”) where the pentlandite had been. Ni derived from the pentlandite was incorporated into ferrihydrite, onto the surface of which the Ni,Na sulfate Ni-bloedite formed.Based on the size and abundant “corrosions” within pyrrhotite grains, combined with observations from other authors, we conclude that Orgueil and Ivuna have undergone a greater degree of alteration than Alais and Tonk. Further work is needed to assess the conditions under which pentlandite would be dissolved preferentially to pyrrhotite, as the study of terrestrial literature indicates that the latter mineral is preferentially removed.     

郭山高岭土铁钛赋存状态的分析电子显微术研究

使用分析电子显微术对福建郭山高岭土中铁、钛元素的赋存状态进行了研究。结果表明,高岭土中铁钛的赋存状态分为两类,一类为参加到粘土矿物晶格中的铁和钛,简称为结构铁、结构钛;另一类为游离出现或吸附在高岭矿物(高岭石和埃洛石)颗粒表面的铁、钛矿物。查明了在全铁和全钛中,结构铁和结构钛仅占少数,大部分以铁、钛独立矿物形式出现。从而确定了可将高岭土粘粒级(<2μm)中铁、钛含量降低到的最低限度,这便为提高高岭土品级和经济价值提供了可靠的依据。     

Disproportionation of Fe<Superscript>2+</Superscript> in Al-free silicate perovskite in the laser heated diamond anvil cell as recorded by electron probe microanalysis of oxygen

Experimental evidence is reported for Fe²⁺ disproportionation in Al-free perovskite (Pv), when submitted to large temperature gradients (i.e., under off-equilibrium conditions) in a laser heated diamond anvil cell (LHDAC). To enable this effect, the experimental procedure was designed to produce large radial and axial temperature gradients. In the Pv and ferropericlase (Fp) assemblage synthesized after dissociation of natural olivine, the three chemical states of iron (i.e., Fe⁰, Fe²⁺ and Fe³⁺) could be evidenced by electron probe microanalysis (EPMA), through variations of oxygen contents attached to the Fe cations. Despite inherent difficulties for determination of O-contents and Fe³⁺/ΣFe ratios using EPMA, we recorded significant changes in iron oxidation state across the laser-heated strip. These changes are correlated with variations in composition for the major elements (Fe, Mg, and Si), which evidences that the Pv/Fp assemblage experienced large segregation under the strong temperature gradients. Grains of metallic iron were detected in parts of the laser-heated strip coexisting with a Pv phase with Fe/(Mg + Fe) = 6 at% and most of its iron as Fe³⁺. This Fe²⁺-disproportionation reaction involves insertion of Fe³⁺-defects in the Pv lattice. This Fe³⁺-bearing Pv phase is presumably unstable and decomposes into a mineral assemblage including magnesioferrite, which is detected at the border of the laser-heated strip.