Interstratification and other reaction microstructures in the chlorite-berthierine series

 Transmission electron microscopy (TEM) results show there is a series of periodically and nonperiodically interstratified structures composed of berthierine and chlorite layers in low-temperature “chlorite” that is one of the alteration products of granulite-facies Archean ironstone from the eastern border of the Beartooth Mountains, Montana. An antiphase domain structure suggests that the interstratified structures are intermediate transformation products formed by reaction from berthierine (serpentine structure) to chlorite. Periodically interstratified structures consisting of chlorite (C) and serpentine-like (S) (or berthierine) layers include (CS), (CCS), (CCCS), (CCCCS), and (CCCCCCS). The layer sequences in interstratified chlorite-berthierine are indicative of the reaction mechanisms that produce the interstratified structures (e.g., crystallization from solution or solid-state transformation). The reaction from berthierine to chlorite is crystallographically much like a cell-preserved phase transformation, even though it is highly reconstructive. Berthierine can be considered a polymorph of the Fe-rich chlorite mineral chamosite, with berthierine as the los-temperature phase. Interstratification and integrowths in the chlorite-berthierine series may be common phenomena in low-temperature layer silicates resembling chlorite. Although such relations are difficult to recognize from chemical analyses or powder X-ray diffraction patterns, they can be observed readily with TEM method. Received: 25 April 1995/Accepted 5 April 1996     

Kulkeite,a new metamorphic phyllosilicate mineral: Ordered 1∶1 chlorite/talc mixed-layer

Kulkeite occurs as platy, colorless, porphyroblastic, single crystals up to 2 mm in size in a low-grade dolomite rock associated with a Triassic meta-evaporite series at Derrag, Tell Atlas, Algeria, It is associated with sodian aluminian talc, unusual chlorite polytypes, and both K and Na phlogopite. Kulkeite is optically biaxial, negative, n _x=1.552, n _y=1.5605, n _z=1.5610, 2V_z=24° (obs.). Based on microprobe analysis the empirical formula is (Na_0.38K_0.01Ca_0.01)(Mg_8.02Al_0.99)[Al_1.43Si_6.57O₂₀](OH)₁₀ with some variation in Na, Si, and tetrahedral Al. The crystals are monoclinic with a=5.319(1), b=9.195(2), c=23.897(10) Å, β=97° 1(3)′; Z=2; the calculated density is 2.70 g cm^?3. The four strongest lines in the X-ray powder pattern are (d, I, hkl): 7.90, 100, 003; 1.533, 100, 060; 7.42, 80, 002; 3.38, 80, 007; the 001 reflection with 23.7 Å has intensity 10. Transmission electron microscopy confirms the nature of a regular 1∶1 mixed-layer, which consists of 14 Å chlorite (clinochlore) sheets alternating with sheets of one-layer (9.5 Å) talc characterized by the lattice substitution NaAl→Si just as in the talc occurring as a discrete mineral co-existing with kulkeite. Kulkeite is intergrown with lamellae of clinochlore that represent two-layer and five-layer (70 Å) polytypes with optical birefringence exceeding the normal value for clinochlore by a factor of 3. The origin of kulkeite is due to low-grade metamorphism with temperatures probably not exceeding 400° C. As the clinochlore lamellae and sodian aluminian talc are found in mutual contact, kulkeite seems to represent a metastable mineral at least during the latest phase of metamorphism. However, at an earlier stage, prior to clinochlore formation, kulkeite might have been stable, and the incorporation of Na and Al into its talc component could indeed be the decisive factor for the formation of the mixed-layer.     

Pre-ore hydrothermal alteration in an unconformity-type uranium deposit

 Hydrothermal alteration associated with the formation of unconformity-type uranium deposits is manifested mainly by intense chloritic replacement of metamorphic mineral assemblages. At the Koongarra deposit (northern Australia), three stages of pre-ore alteration were identified in chloritized metamorphic muscovite using optical microscopy, the electron microprobe, and transmission and analytical electron microscopy (TEM and AEM). During the first stage metamorphic muscovite was altered to a mica with very low interlayer occupancy (K content as low as 0.35 compared to 1 for ideal muscovite), high octahedral cation content (up to 2.3 whereas ideal muscovite has 2) and high Si content. High resolution TEM images show that these changes in composition were accompanied by frequent layer terminations in contrast to the metamorphic muscovite, whereas selected area electron diffraction patterns indicate that the altered muscovite remained a two-layer polytype. The alteration of muscovite appears more extensive in the outer alteration halo and has been almost completely eradicated in the ore zone where chloritization is more complete. During the second stage of the pre-ore alteration the altered muscovite was replaced by Mg-rich serpentine (lizardite) and clinochlore. High resolution TEM images show two 10 A˚ mica layers coalescing to one 14 A˚ chlorite layer. This type of coalescence appears to involve transformation of one dioctahedral layer of the mica structure to one trioctahedral brucite layer in the chlorite structure through dissolution of the tetrahedral sheets and cation influx in the octahedral site. The final stage of the pre-ore alteration resulted in replacement of lizardite and clinochlore by Fe-rich chlorite. Comparison of the alteration observed in metamorphic muscovite with the alteration observed in metamorphic biotite and garnet shows clearly that chloritization of these phases was also a pre-ore alteration event. Pre-ore alteration was principally characterized by the evolution of chlorite from a Mg-rich phase to an Fe-rich one. Received: 29 July 1994/Accepted: 8 January 1995     

中国含油气盆地粘土矿物的某些矿物学特征

本文总结归纳了２０多个含油气盆地粘土矿物的类型，讨论了８种较常见的、６种较少见的和３种极少见的粘土矿物的Ｘ射线衍射特征及其成分、形态和分布等方面的矿物学特征．     

The clay mineralogy of the Scottish Dalradian meta-limestones

The clay mineralogy of the Scottish Dalradian meta-limestones has been studied mainly by X-ray diffraction. In the samples from the north-east part of the Dalradian outcrop, which often show evidence of intense metamorphism, clay minerals found include saponite, regularly and irregularly interstratified smectite-chlorite, swelling chlorite, normal chlorite, illite and kaolinite. Limestones from the weakly metamorphosed South-West Highlands area contain only kaolinite, illite and chlorite. The genesis of the clay minerals is considered, particular attention being paid to the swelling minerals from the north-east region.     

Phlogopite-chlorite reaction mechanisms and physical conditions during retrograde reactions in the Marble Formation,Franklin, New Jersey

A retrograde assemblage in a specimen from the Franklin Marble Formation containing an unusual occurrence of three micas has been studied. Microprobe analyses of the margarite, muscovite and phlogopite reveal significant sodium and fluorine but otherwise show little mutual solid solution. The conditions that prevailed during the retrogression estimated from phase equilibria are T=370–450° C and =0.03–0.3 at an assumed pressure of 2 kb.Examination of the phlogopite by TEM revealed replacement of phlogopite by chlorite. The chlorite occurred as small packets of layers interlayered with phlogopite. AEM analyses revealed that the chlorite composition approximates that of clinochlore. Transformations from a single phlogopite layer to one chlorite layer (a 11 reaction) and also from two phlogopite layers to one chlorite layer (a 21 reaction) have been observed. Both reactions result in a large volume change causing local strain at transition fronts. An apparently strain-free, volume-preserving transformation of 14 phlogopite layers terminating against 10 chlorite layers was observed which indicates that pervasive replacement may occur through a combination of both reactions. Topological and site occupancy changes during the transformation suggest that the reaction involves not only gain and loss of layer units, but also considerable local rupturing and reformation of bonds, concomitant with ion diffusion and interchange. Dislocations (layer terminations) at the transition front imply the existence of pathways for the fluid flow and ion transport required for mass balance.Contribution No. 397 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan, USA     

Reaction progress in chloritic material: an electron microbeam study of the Taveyanne greywacke, Switzerland

Chlorite and associated minerals from the volcanogenic Taveyanne metasediment of the western Helvetic nappes, Switzerland, were investigated by electron microprobe (EMP) and transmission electron microscopy (TEM) in order to determine their textural and chemical evolution during low-temperature metamorphism. EMP analyses of chloritic material from sub-greenschist facies outcrops show a decrease of Si and Σ(Ca, Na, K) with increasing metamorphic grade. A number of conclusions may be drawn from combined TEM images and analytical electron microscopy (AEM) data. 1 In diagenetic-grade samples, chlorite crystals (observed maximum defect-free distance=80 nm) always contain some 1 nm layers (with a maximum of 29% of all layers) and less frequently some 0.7 nm berthierine-like layers. With increasing grade, the amounts of 1 and 0.7 nm layers decrease, and most chlorite from the epizone is structurally pure or contains less than 2% of 1 nm layers. 2 A positive correlation was found between the amount of 1 nm layers and the Ca+K+Na content, indicating that the 1 nm layers are saponite. 3 Observations and calculations suggest that the transformation reaction of saponite to chlorite takes place by the replacement of the interlayer cations in saponite by brucite-like layers resulting in a local volume decrease. In contrast, the destruction of berthierine has only minor influence on the local bulk volume. These results confirm recent studies which show that the change in composition measured by EMP of diagenetic-grade chloritic material are mainly the result of mixtures of chlorite and saponite. The use of chlorite ‘geothermometry’ in such systems is greatly influenced by the presence of saponite and hence is not based on reaction equilibria, even though temperatures calculated in this study agree with temperatures derived from other methods. Therefore, chlorite evolution should be treated as a kinetically controlled grade indicator and developed as a qualitative scale similar to the illite crystallinity index.     

Clay mineralogy of Triassic sediments in southern Israel and Sinai

The clay mineral composition of Triassic sediments in the Negev and Sinai depends upon the environment of deposition. Kaolinite predominates in continental and epicontinental sediments. The mineralogical composition of the marine clays resembles that of corresponding samples from North Africa and Europe, which comprise various mixtures and interstratifications of illite, montmorillonite, vermiculite and chlorite. Evaporitic sediments are poor in clay minerals and those present are largely detrital. The results presented suggest that chlorite was formed diagenetically by prolonged percolation of seawater through pervious layers overlying impervious ones (hard beds).     

Clay petrology of the Upper Triassic/Lower Jurassic terrestrial strata of the Newark Supergroup,Connecticut Valley,U.S.A.

The clay mineralogy of the Newark Supergroup (Upper Triassic/Lower Jurassic) in the Connecticut Valley was studied by X-ray diffraction analysis. Clay minerals identified in 126 samples are illite, chlorite, smectite, kaolinite, vermiculite, expandable chlorite, mixed-layer illite/smectite, mixed-layer chlorite/smectite, and mixed-layer chlorite/vermiculite. In general, the rocks are illitic with subordinate amounts of chlorite. However, the various lithofacies in the Newark Supergroup are characterized by distinct clay-mineral assemblages. Red beds of floodplain origin contain clays mainly of detrital nature with 2M illite most abundant. Subordinate amounts of chlorite, smectite, vermiculite, kaolinite and mixed-layer illite/smectite are also present. An interstratified chlorite/vermiculite occurs in red mudstone underlying basalt flows. Lacustrine gray beds are generally characterized by the clay-mineral assemblage 1Md illite + chlorite with minor amounts of smectite ane expandable chlorite. An interstratified chlorite/smectite predominates in gray mudstone associated with perennial lake cycles in the East Berlin Formation. Black shales of deeper lacustrine origin contain the assemblage 1Md ifillite + trioctahedral smectite and traces of chlorite. Illite and smectite also occur as mixed-layer phases.In many respects, the distribution of clay minerals in the Connecticut Valley can be likened to the general scheme proposed for the Permo-Triassic basins of Europe and Africa. These display both vertical and horizontal variations in clay-mineral assemblages that reflect the chemical and spatiotemporal evolution of intrabasin depositional and diagenetic environments. Chemical data indicate that magnesium, especially, was concentrated in the black muds of large perennial lakes that intermittently occupied the Connecticut rift valley. Pore waters derived from these sediments played an important role in the development of Mg-rich 2 : 1 and interstratified clay minerals during early diagenesis.     

西藏羊八井地热田水热蚀变

本文对羊八井地热田钻扎ZK-201、ZK-301和ZK-308的岩心进行了较系统的蚀变矿物学、岩石学和流体包体研究。划分出6个蚀变矿物共生组合及蚀变分带,讨论了蚀变过程中岩石化学变化的特点,并推测了蚀变的温度和酸碱度条件。研究表明,热田曾处于极度的活动状态,最高温度达220-240℃,由于冷水的入侵,热田在目前钻探所及范围已冷却了50-70℃。蚀变矿物分布模式表明,目前热田流体主通道位于北部,热田进一步的开发应以寻找北部深部高温流体为主。     

Corrensite and mixed-layer chlorite/corrensite in metabasalt from northern Taiwan: TEM/AEM,EMPA, XRD,and optical studies

Many chloritic minerals in low-grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties, expand slightly upon glycolation (expandable chlorite) and/or have excess Al^VI relative to Al^IV, as well as significant Ca, K and Na contents. Chloritic minerals with these properties fill vesicles and interstitial void space in low-grade metabasalt from northern Taiwan and have been studied with a combination of TEM/AEM, EMPA, XRD, and optical microscopy. The chloritic minerals include corrensite, which is an ordered 1:1 mixed-layer chlorite/smectite, and expandable chlorite, which is shown to be a mixed-layer chlorite/corrensite. Corrensite and some mixed-layer chlorite/corrensite occur as rims of vesicles and other cavities, while later-formed mixed-layer chlorite/corrensite occupies the vesicle cores. The TEM observations show that the mixed-layer chlorite/corrensite has ca. 20%, and the corrensite has ca. 50% expandable smectite-like layers, consistent with XRD observations and with their abnormal optical properties. The AEM analyses show that high Si and Ca contents, high Al^VI/Al^IV and low Fe^VI/(Fe+Mg)^VI ratios of chlorites are correlated with interstratification of corrensite (or smectite-like) layers in chlorite. The AEM analyses obtained from 200–500 Å thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low Al^IV/Si^IV and low Fe^VI/(Fe+Mg)^VI, while chlorite has high Al^IV/Si^IV and high Fe^VI/(Fe+Mg)^VI. This implies that the trioctahedral smectite-like component of corrensite has significantly lower Al^IV/Si^IV and Fe^VI/(Fe+Mg)^VI. The ratios of Fe^VI/(Fe+Mg)^VI and Al^IV/Si^IV thus decrease in the order chlorite, corrensite, smectite. The proportions of corrensite (or smectite-like) layers relative to chlorite layers in low-grade rocks are inferred to be controlled principally by Fe/Mg ratio in the fluid or the bulk rock and by temperature. Compositional variations of chlorites in low-grade rocks, which appear to correlate with temperature or metamorphic grade, more likely reflect variable proportions of mixed-layered components. The assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases, such as chlorite-corrensite, corrensite-smectite, or chlorite-corrensite-smectite. A model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1:1 ordered mixed-layer chlorite/smectite.     

我国二八面体绿泥石的发现及其混层矿物的研究

绿泥石作为重要的粘土矿物已被广泛研究。然而,多数属于三八面体亚群。自从α-绿泥石、端铅绿泥石(Nagolnit)以及片硅铝石(donbassite)发现以后,才开始确认二八面体绿泥石的存在。     

Evolution of borate minerals from contact metamorphic to hydrothermal stages: Ludwigite-group minerals and szaibélyite from the Vysoká – Zlatno skarn,Slovakia

Mineralogy and Petrology - Borate minerals of the ludwigite group (LGM) and szaibélyite in association with hydroxylclinohumite, clinochlore, a serpentine mineral, magnesian magnetite, spinel,...     

Contribution of long-term hydrothermal experiments for understanding the smectite-to-chlorite conversion in geological environments

The smectite-to-chlorite conversion is investigated through long-duration experiments (up to 9 years) conducted at 300 °C. The starting products were the Wyoming bentonite MX80 (79 % smectite), metallic iron and magnetite in contact with a Na–Ca chloride solution. The predominant minerals in the run products were an iron-rich chlorite (chamosite like) and interstratified clays interpreted to be chlorite/smectite and/or corrensite/smectite, accompanied by euhedral crystals of quartz, albite and zeolite. The formation of pure corrensite was not observed in the long-duration experiments. The conversion of smectite into chlorite over time appears to take place in several steps and through several successive mechanisms: a solid-state transformation, significant dissolution of the smectite and direct precipitation from the solution, which is over-saturated with respect to chlorite, allowing the formation of a chamosite-like mineral. The reaction mechanisms are confirmed by X-ray patterns and data obtained on the experimental solutions (pH, contents of Si, Mg, Na and Ca). Because of the availability of some nutrients in the solution, total dissolution of the starting smectite does not lead to 100 % crystallization of chlorite but to a mixture of two dominant clays: chamosite and interstratified chlorite/smectite and/or corrensite/smectite poor in smectite. The role of Fe/(Fe + Mg) in the experimental medium is highlighted by chemical data obtained on newly formed clay particles alongside previously published data. The newly formed iron-rich chlorite has the same composition as that predicted by the geothermometer for diagenetic to low-grade metamorphic conditions, and the quartz + Fe-chlorite + albite experimental assemblage in the 9-year experiment is close to that fixed by water–rock equilibrium.     

The smectite–chlorite transition in drillhole NJ-15, Nesjavellir geothermal field, Iceland: XRD, BSE and electron microprobe investigations

Abstract In well NJ-15 of the Nesjavellir geothermal field, Iceland, the transition of discrete smectite into discrete chlorite has been studied from drill cuttings recovered at depths of less than 1714 m and over a continuous range of temperatures between 60 and 300° C. At temperatures below 180° C, the clay fractions contain mixtures of di- and trioctahedral smectites, whose layer charge increases with depth. Between 200 and 240° C, discrete smectites have transformed into smectite-rich, randomly interstratified chlorite and smecite ( R 0 C/S). Because the abundance of chlorite interlayers in this C/S is generally <20%, its presence can be detected only by electron microprobe techniques and not by X-ray diffraction. Between 245 and 265° C, both regularly ( R 1) and randomly interstratified C/S are the predominant layer silicates. Discrete chlorite first appears at approximately 270° C and coexists with minor amounts of R 0 C/S at higher temperatures.
R 0 and R 1 C/S form a nearly complete compositional series between trioctahedral saponite and discrete chlorite end-members. The interlayer cation and Si content of smectites and C/S decrease with increasing temperature. The Mg/(Mg + Fe) content of smectite, C/S, and chlorite is unrelated to temperature. The percentage of chlorite in C/S, as determined by electron microprobe analyses, increases continuously with increasing temperature, except for occurrences of smectite-rich C/S in fresh basaltic dykes which have not thermally equilibrated with the higher grade country rocks.     

云南腾冲地热区主要蚀变矿物含量与蚀变母岩的关系

腾冲地热区出露有众多热泉泉群,地热活动频繁,岩石发生强烈蚀变,形成的主要蚀变矿物包括高岭石、绢云母、蒙脱石、I/M间层矿物、石英和蛋白石。主要蚀变矿物的种类和含量受蚀变母岩性质的控制,花岗质砂砾岩和花岗岩形成高岭石,玄武岩形成伊利石和蒙托石,安山岩中发育硅化作用。泥化作用增强的趋势是安山岩→花岗岩→玄武岩→花岗质砂砾岩。由于花岗质砂砾岩在热区内广泛分布,通过蚀变作用形成了有经济价值的高岭土矿床。     

Microstructures and compositional variation in the intravolcanic bole clays from the eastern Deccan volcanic province: Palaeoenvironmental implications and duration of volcanism

Clay minerals associated with intra-volcanic bole horizons of varied colours and thicknesses contain montmorillonite, halloysite and kaolinite, show distinct microstructures and microaggregates. In kaolinite, Fe³⁺ ions substitute for Al³⁺ at octahedral sites. Most of these clays are dioctahedral type, show balance between net layer and interlayer charges. The interstratified illite — smectite (I/S) mixed layers containing variable proportions of montmorillonite. Illite contains sheet-like, well oriented microaggregates. The parallel stacks of chlorite sheets show chlorite/smectite (C/S) mixed layers. Progressive enrichment of Fe and depletion of Al ions with the advancement of kaolinization process is observed. High order of structural and compositional maturity observed in these bole clays, indicate long hiatus between the two volcanic episodes.     

Natural speciation of nickel at the micrometer scale in serpentine (ultramafic) topsoils using microfocused X-ray fluorescence,diffraction, and absorption

Serpentine soils and ultramafic laterites develop over ultramafic bedrock and are important geological materials from environmental, geochemical, and industrial standpoints. They have naturally elevated concentrations of trace metals, such as Ni, Cr, and Co, and also high levels of Fe and Mg. Minerals host these trace metals and influence metal mobility. Ni in particular is an important trace metal in these soils, and the objective of this research was to use microscale (µ) techniques to identify naturally occurring minerals that contain Ni and Ni correlations with other trace metals, such as Fe, Mn, and Cr. Synchrotron based µ-XRF, µ-XRD, and µ-XAS were used. Ni was often located in the octahedral layer of serpentine minerals, such as lizardite, and in other layered phyllosilicate minerals with similar octahedral structure, such as chlorite group minerals including clinochlore and chamosite. Ni was also present in goethite, hematite, magnetite, and ferrihydrite. Goethite was present with lizardite and antigorite on the micrometer scale. Lizardite integrated both Ni and Mn simultaneously in its octahedral layer. Enstatite, pargasite, chamosite, phlogopite, and forsterite incorporated various amounts of Ni and Fe over the micrometer spatial scale. Ni content increased six to seven times within the same 500 µm µ-XRD transect on chamosite and phlogopite. Data are shown down to an 8 µm spatial scale. Ni was not associated with chromite or zincochromite particles. Ni often correlated with Fe and Mn, and generally did not correlate with Cr, Zn, Ca, or K in µ-XRF maps. A split shoulder feature in the µ-XAS data at 8400 eV (3.7 Å^?1 in k-space) is highly correlated (94% of averaged LCF results) to Ni located in the octahedral sheet of layered phyllosilicate minerals, such as serpentine and chlorite-group minerals. A comparison of bulk-XAS LCF to averaged µ-XAS LCF results showed good representation of the bulk soil via the µ-XAS technique for two of the three soils. In the locations analyzed by µ-XAS, average Ni speciation was dominated by layered phyllosilicate and serpentine minerals (76%), iron oxides (18%), and manganese oxides (9%). In the locations analyzed by µ-XRD, average Ni speciation was dominated by layered phyllosilicate, serpentine, and ultramafic-related minerals (71%) and iron oxides (17%), illustrating the complementary nature of these two methods.

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间层矿物的结构参数与分类探讨

从间层的概念出发，对四个间层结构参数的定义和意义进行总结，并根据间层矿物的结构和组成对其进行了分类探讨。首先根据晶层种类将间层矿物分为同类结构基元间层矿物和异类结构基元间层矿物两大类，然后根据变差系数划分出规则间层矿物和不规则间层矿物，最后根据间层比、连接概率等特征划分出有序间层、无序间层和带状间层。     

X射线粉晶衍射仪在辽宁瓦房店金伯利岩蚀变矿物鉴定中的应用

瓦房店金伯利岩热液蚀变强烈,原岩矿物组分几乎蚀变殆尽,显微镜下对蚀变矿物鉴定相当困难.利用X射线粉晶衍射技术对蚀变金伯利岩物相进行系统检测,结果显示：42号岩管金伯利岩主要矿物为蛇纹石、金云母和滑石,有少量方解石、锐钛矿、磷灰石、石英、钛铁矿、钙钛矿、榍石、磁铁矿和绿泥石;石灰窑1号无矿金伯利岩岩管主要矿物为蛇纹石、金云母和白云石,有少量方解石、锐钛矿、磷灰石、滑石、磁铁矿和绿泥石;9号无矿金伯利岩岩脉主要矿物为方解石和石英,有少量绿泥石和重晶石;51号贫矿金伯利岩岩管主要矿物为蛇纹石和金云母,方解石化作用不均匀,白云石化作用普遍,有少量锐钛矿、滑石、磁铁矿、绿泥石、磷灰石、钛铁矿、石英;30号贫矿岩管样品风化严重,主要矿物为蒙脱石,有少量方解石、滑石、蛇纹石、榍石、磷灰石.实践证明,采用X射线粉晶衍射仪鉴定金伯利岩蚀变矿物组合是一种非常可行的技术手段.