X-ray study of the nature of stacking faults in the structure of glauconites

Sakharov, B. A.; Besson, Gérard; Drits, Victor A.; Kameneva, M. Yu.; Salyn, A. L.; Smoliar, B. B.

doi:10.1180/claymin.1990.025.4.02

Cited by 43 publications

(32 citation statements)

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“…Note that the decomposition of the MiJ:+'sbauer spectrum of sample 68/69 was carried out by Dr Bonnin under conditions when Fe 3+ isomer shifts have been constrained to be equal. (Sakharov et al, 1990). In accordance with the diffraction features for dioctahedral tv 1M mica, XRD patterns contain strong lli, 112 and 112 reflections, whereas the 111 reflection has zero intensity.…”

Section: Mossbauer Spectra: Data Collectionmentioning

confidence: 63%

Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies

et al. 1997

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AB S TRACT: Celadonite, glauconite and Fe-illite samples were studied by XRD, EXAFS, IR and M6ssbauer spectroscopy. The samples were monomineralic and corresponded to IM polytype. In the OH-stretching region of the IR spectra the content of each definite pair of cations bonded to OH groups was determined. The number of heavy (Fe) and light (AI, Mg) octahedral cations nearest to Fe was found by the EXAFS technique. The predicted quadrupole splitting values for each definite arrangement of cations nearest to Fe 3+ were used to interpret the M6ssbauer spectra. After the fitting procedure, the intensity of each doublet corresponded to a definite set of local cation arrangements around Fe 3+ and to a definite occurrence probability of these arrangements. Computer simulation and the experimental data obtained were used to reconstruct the distribution of isomorphous octahedral cations in the 2:1 layers. For all samples, R 2+ cations prefer to occupy one of the two symmetrically independent cis-sites and RZ+-R 2+ and/or AI-Fe 3+ were prohibited in the directions forming _+ 120 ~ with the b axis. Therefore, octahedral sheets of the samples revealed domain structure, in which domains differ in size, in the nature of predominant cation and/or by cation ordering.One of the characteristic features of phyllosilicates and, in particular, dioctahedral micas, is a wide variation of chemical compositions. Different samples of the same mineral may differ not only in octahedral and tetrahedral cation contents of 2:1 layers, but also in their long-and short-range ordering in isomorphous cation distribution. Determination of the actual cation distribution in dioctahedral micas is a complex problem. X-ray diffraction (XRD) yields data only on the averaged composition of cations in the unit-cell sites, ignoring a possible short-range ordering. For finely dispersed minerals containing stacking faults, even this information is often difficult to obtain.Spectroscopic methods are, therefore, especially useful, since they probe local atomic environments and have a potential to determine short-range cation ordering. Utilization of spectroscopic methods, however, often meets certain difficulties. One of the main problems is that most of these methods are indirect, that is, they provide indirect structural information about a sample under study. For this reason, interpretation of spectroscopic data is not always feasible or properly based.One of the effective ways to determine the actual cation distribution consists of the application of complex diffraction and spectroscopic methods to the same sample. Obviously, the greater the number of methods involved, the more comprehensive the structural information obtained. Each method, however, has its own advantages and limitations and therefore provides only a partial solution to a 9 1997 The Mineralogical Society 154 K A. Drits et al.general problem of cation order/disorder in dioctahedral mica structures. Therefore, even if unambiguous interpretation of experimental data is provided, the actual ca...

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Section: Mossbauer Spectra: Data Collectionmentioning

confidence: 63%

Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies

et al. 1997

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“…The mica-structure simulation program was applied to the study of the nature of stacking faults in glauconite and iUite structures using comparison of experimental diffraction curves with those calculated for structural models containing various defect types (Sakharov et al, 1990;Sakharov, 1991). Correct assignment of the atomic coordinates in the layer unit-cell was required to obtain satisfactory agreement between the intensity distributions in calculated and experimental XRD curves.…”

Section: Applicationsmentioning

confidence: 99%

“…Second, structural features are predicted and atomic coordinates are calculated, using a specially devised computer program, from the data on chemical composition and cell parameters of dioctahedral and trioctahedral micas having disordered cation distribution. Such calculations are useful to interpret infrared (IR), M6ssbauer and EXAFS spectroscopic data for monomineral samples, to simulate XRD patterns, and to aid in electrostatic energy calculations and estimations of O-H vector 9 1993 The Mineralogical Society orientation (Slonimskaya et al, 1986, Daynyak et al, 1984Drits & Tchoubar, 1990;Sakharov et al, 1990;Bookin et al, 1982).…”

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confidence: 99%

Relationships between Structural Parameters and Chemical Composition of Micas

Smoliar-Zviagina

1993

Clay miner.

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A B S T R A C T :Regression analysis of high-precision structural and chemical data on trioctahedral and dioctahedral micas yielded interrelationships between unit-cell parameters, chemical composition and structural details. Regression equations relating b and csinfl parameters of micas to composition were used for estimating composition from cell data in order to analyse P-T conditions of rock formation. Algorithms for computing atomic coordinates for 2M1, 3T and IM dioctahedral micas having either centrosymmetric or non-centrosymmetric layers and 1M trioctahedral micas are presented. Deviations of computed atomic coordinates from experimental values are, on average, 0-002 A for octahedral cations and 0.005-0.010 ,~ for other atoms. Discrepancies between calculated and experimental individual interatomic distances seldom exceed 0.01 A. Computed atomic coordinates were used to calculate X-ray diffraction patterns for glauconite and illite. Results indicate a close fit between the calculated and experimental patterns. The local structure around an octahedral cation of interest can be determined.Diverse isomorphous cation substitutions depending on bulk chemistry and rock formation conditions lead to considerable variations in phyllosilicate structural features. Direct diffraction structure analysis, however, is rarely done, not only because of the expense and time involved in the procedure but also because suitable single crystals are difficult to find. Furthermore, phyllosilicates are often clay-sized, poorly crystallized and impure, thereby making interpretation of diffraction and spectroscopy data problematic. Various simulation procedures to overcome this difficulty should involve modelling of the average structure and/or local structural fragments. On the other hand, even direct chemical analysis of each component in a polymineral sample is not always feasible. It is of interest, therefore, to develop methods to allow detailed structural and crystal-chemical information to be deduced from easily obtainable data, such as bulk chemical analysis and X-ray diffraction (XRD) powder patterns.Two aspects of this problem are developed in this paper. First, cell parameters and chemical composition of dioctahedral micas are examined for interrelationships. This is useful for estimating compositions of polycomponent samples for which direct chemical analysis is laborious or expensive, and for evaluating the degree of transformation of lowand medium-grade metamorphic rocks. Second, structural features are predicted and atomic coordinates are calculated, using a specially devised computer program, from the data on chemical composition and cell parameters of dioctahedral and trioctahedral micas having disordered cation distribution. Such calculations are useful to interpret infrared (IR), M6ssbauer and EXAFS spectroscopic data for monomineral samples, to simulate XRD patterns, and to aid in electrostatic energy calculations and estimations of O-H vector 9 1993 The Mineralogical Society

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“…Even for samples that produce sharp reflections, it might not be possible to detect admixture of small amounts of either with large amounts of the other. Figure 6 compares the Potsdam illite with the Devonian Kalkberg K-bentonite (Reynolds and Hower, 1970) after heating to 350~ The two patterns are similar, although the broad 20/:I3/reflections for the Kalkberg sample indicate particle-size broadening, and the 02/: 11 l peaks are additionally broadened by n. 120 ~ rotational stacking disorder (n. 60 ~ disorder is minimal, based on 20l: 13l peak resolution, which is diminished by this type of disorder; see Sakharov et al, 1990). Patterns similar to those in Figure 6 have been reported by Reynolds (1992) for K-bentonites from the overthrust belt of Montana, though they were identified as 3T or twinned tv-lM polytypes; and diffraction patterns like that of the Potsdam illite have been noted for illites from the Rotliegendes (North Sea Basin) and Mount Simon (Illinois Basin) sandstones (Mingchou Lee, personal communication, 1992).…”

Section: Three-dimensional Structurementioning

confidence: 99%

“…Parameters for a 1M structure were obtained from the simultaneous solution of two expressions to give a, c, and ~ (Sakharov et al 1990). Drits et al (1984) is shown by Table 3.…”

Section: Three-dimensional Structurementioning

confidence: 99%

Illite from the Potsdam Sandstone of New York: A Probable Noncentrosymmetric Mica Structure

Reynolds

Thomson

1993

Clays and clay miner.

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Abstract--Illite from the Potsdam Sandstone (lower Ordovician) of Northwestern New York was studied by powder X-ray diffraction, scanning electron microscopy, and chemically analyzed and dated by the K/Ar method. The texture and ages of 360 and 392 Ma on two samples establish that the mineral is authigenie and relatively uncontaminated by Precambrian detritus. Random powder X-ray diffraction patterns show sharp and relatively intense 02l and 1 ll reflections, indicating an ordered structure. Comparisons with calculated patterns demonstrated that the mineral is not the common 1Mor 2M~ polytype. Instead, the experimental pattern is very similar to that of a 3T polytype, but it agrees better with the calculated pattern of the octahedral cis-vacant, noncentrosymmetric (space group C2) structure found by M6ring and Oberlin (1967) and Tsipursky and Drits (1984) in smectites, proposed for mica by and found by Zvyagin et al. (1985).

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X-ray study of the nature of stacking faults in the structure of glauconites

Cited by 43 publications

References 3 publications

Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies

Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies

Relationships between Structural Parameters and Chemical Composition of Micas

Illite from the Potsdam Sandstone of New York: A Probable Noncentrosymmetric Mica Structure

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