A new collection of clay mineral ‘Crystallinity’ Index Standards and revised guidelines for the calibration of Kübler and Árkai indices

AbstractClay mineral ‘Crystallinity Index Standards’ (CIS) composed of Palaeozoic mudrocks from southwest England were investigated systematically in five sub-fractions per sample for the first time. X-ray diffraction was used to determine mineral assemblages, calibrated 001 illite full-width-at-half-maximum (FWHM) values and illite polytype compositions, in addition to K–Ar isotopic analyses of all fine fractions. The FWHM results of the <2 µm fraction are consistent with previous studies and reflect the range of diagenetic to epizonal grades covered by the sample set SW1 to SW7 (~0.61–0.26°2θ). Diagenetic and lower anchizone samples also show significant broadening of 001 illite reflections in the finer fractions and contain mixtures of authigenic 1M + 1Md illite and detrital 2M1 white mica polytypes suitable for illite age analysis. The estimated end-member ages of the Bude (SW1-1992) and younger Crackington (SW3-2000) mudstones yield detrital ages of Late Cambrian to Middle Ordovician (493–457 Ma) and a broad range of 1M + 1Md illite ages between Middle Permian and Early Jurassic (271–190 Ma). The detrital age of the stratigraphically older Crackington Formation mudrock (SW2-1992) is Late Devonian (384–364 Ma) with 1M + 1Md illite ages between Late Triassic and Early Jurassic (219–176 Ma). The origin of Mesozoic 1M + 1Md illite ages may represent neocrystallized illite associated with Mesozoic hydrothermal events or similar events that thermally reset older authigenic illite with partial loss of radiogenic argon and no renewed crystal growth. In contrast, upper anchizonal and epizonal Devonian slates (SW3-2012, SW4-1992, SW6-1992 and SW7-2012) contain only the 2M1 polytype, with K–Ar ages younger than the stratigraphic age. The three finest fractions of SW4-1992 yield consistent Late Carboniferous ages (331–304 ± 7 Ma) that are considered to date the neocrystallized 2M1 mica. Most fractions of epizonal slate (SW6-1992, SW7-2012) yield Early Permian ages (293.6–273 Ma) corresponding to published cooling ages of the Tintagel High-Strain Zone and the intrusion of the Bodmin granite (291.4 ± 0.8 Ma). These first K–Ar age constraints for the fine fractions of the CIS should provide useful reference values for testing analytical procedures of illite age analysis.

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Clay Minerals ◽

10.1180/clm.2018.42 ◽

2018 ◽

Vol 53 (3) ◽

pp. 339-350 ◽

Cited By ~ 5

Author(s):

Laurence N. Warr

Keyword(s):

Clay Mineral ◽

Lower Boundary ◽

Crystallinity Index ◽

Measurement Methods ◽

Peak Width ◽

X Ray Diffraction ◽

X Ray ◽

Kübler Index ◽

Boundary Limits ◽

Mineral Crystallinity

ABSTRACTA new set of clay mineral ‘Crystallinity’ Index Standards (CIS) is available for improved calibration of the half-peak-width values of the X-ray diffraction 001 illite reflection (the Kübler index) and the 002 chlorite reflection (the Árkai index), two widely used indices for determining the state of prograde diagenesis and low-temperature metamorphism. Calibration using mudrock standards removes the numerical differences between laboratories caused by variations in sample preparation, machine settings and measurement methods, thus avoiding erroneous grade determinations. The number of standards available has been increased to nine. These can be used to obtain Kübler index values for each CIS sample and Árkai index values for upper anchizonal and epizonal samples. The diagenetic and lower anchizonal mudrocks are not suitable for Árkai index measurements due to the absence of chlorite or overlap by the 001 kaolinite reflection. Applying the new Kübler-equivalent upper and lower boundary limits of the anchizone placed at 0.32°2θ and 0.52°2θ, respectively (Warr & Ferreiro Mählmann, 2015), the nine standards from the Palaeozoic mudrocks of southwest England now comprise two diagenetic, two lower anchizonal, three upper anchizonal and two epizonal grade samples. These range from weakly cleaved mudstones to strongly foliated slates.

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Standardized clay mineral crystallinity data from the very low-grade metamorphic facies rocks of southern New Zealand

European Journal of Mineralogy ◽

10.1127/ejm/8/1/0115 ◽

1996 ◽

Vol 8 (1) ◽

pp. 115-128 ◽

Cited By ~ 28

Author(s):

Laurence N. Warr

Keyword(s):

New Zealand ◽

Clay Mineral ◽

Low Grade ◽

Metamorphic Facies ◽

Mineral Crystallinity

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The Clay Mineralogy of the Haldon Gravels

Clay Minerals ◽

10.1180/claymin.1973.010.2.04 ◽

1973 ◽

Vol 10 (2) ◽

pp. 87-97 ◽

Cited By ~ 7

Author(s):

R. J. O. Hamblin

Keyword(s):

Clay Mineral ◽

Clay Mineralogy ◽

Crystallinity Index ◽

Peak Height ◽

The Other ◽

Low Grade ◽

X Ray ◽

High Crystallinity ◽

The Matrix ◽

Low Crystallinity

AbstractThe less than 10 μm and less than 3 μm fractions of the heterogenous Haldon Gravels have been examined by X-ray diffractometry. Kaolinite of high to low crystallinity is the dominant clay mineral, with variable amounts of illite (clay mica) ; quartz, a little feldspar and anatase also occur. The kaolinite has been ranked using the crystallinity index of Hinckley and also by indices derived from the ratio of peak height to background height for the 10 and 11 peaks.Clay from the matrix of the psaphitic members of the Buller's Hill Gravel contains intermediate grade kaolinite with a little illite, but clay bodies included in this formation contain only low grade kaolinite with a high, but variable proportion of illite. The Tower Wood Gravel contains two distinct populations; one is identical to that of the Buller's Hill Gravel, the other consists of high crystallinity kaolinite with a little illite. Head Gravel formed from the Buller's Hill Gravel by solifluction contains intermediate to low crystallinity kaolinite.

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Mineralogical, isotopic (K-Ar) and structural-textural characteristics of the Jurassic terrigenous complex in different paleotectonic settings (Greater Caucasus, Chechnya - Georgia)

Moscow University Bulletin. Series 4. Geology ◽

10.33623/0579-9406-2016-1-27-40 ◽

2016 ◽

pp. 27-40

Author(s):

Yu. O. Gavrilov ◽

Yu. V. Kushcheva ◽

I. V. Latysheva ◽

A. I. Gushchin ◽

A. L. Sokolova

Keyword(s):

Clay Mineral ◽

Middle Jurassic ◽

Crystallinity Index ◽

Greater Caucasus ◽

Mineral Associations ◽

Different Types ◽

Northern Zone ◽

Siliciclastic Sediments ◽

Radiometric Characteristics ◽

Terrigenous Complex

The variations in structural, textural, mineralogical and geochemical (radiometric) characteristics in the lower to middle Jurassic siliciclastic sediments of the transect across Chanty-Argun R., Mountain Chechnya and Georgia are considered. This transect crosses areas of different types of deformations from northern zone of weak deformation to southern zone of intensive deformation and cleavage. The southward change in clay mineral associations, polytypical modifications of mica minerals, their crystallinity index, a.o. are observed along the transect. The increase of intensity of secondary alternations of the rocks and dimensions of cleavage enabled the change in K-Ar-system. This is resulted in significantly younger values of measured radiologic age corresponding to older stratigraphic age.

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Low-grade evolution of clay minerals and organic matter in fault zones of the Hikurangi prism (New Zealand)

Clay Minerals ◽

10.1180/clm.2018.46 ◽

2018 ◽

Vol 53 (4) ◽

pp. 579-602 ◽

Cited By ~ 1

Author(s):

Tatiana Maison ◽

Sébastien Potel ◽

Pierre Malié ◽

Rafael Ferreiro Mählmann ◽

Frank Chanier ◽

...

Keyword(s):

Organic Matter ◽

New Zealand ◽

Clay Minerals ◽

Clay Mineral ◽

Structural Characteristics ◽

Mineral Chemistry ◽

Fault Zones ◽

Low Grade ◽

Pore Fluid Chemistry ◽

Mineral Crystallinity

ABSTRACTClay minerals and organic matter occur frequently in fault zones. Their structural characteristics and their textural evolution are driven by several formation processes: (1) reaction by metasomatism from circulating fluids; (2)in situevolution by diagenesis; and (3) neoformation due to deformation catalysis. Clay-mineral chemistry and precipitated solid organic matter may be used as indicators of fluid circulation in fault zones and to determine the maximum temperatures in these zones. In the present study, clay-mineral and organic-matter analyses of two major fault zones – the Adams-Tinui and Whakataki faults, Wairarapa, North Island, New Zealand – were investigated. The two faults analysed correspond to the soles of large imbricated thrust sheets formed during the onset of subduction beneath the North Island of New Zealand. The mineralogy of both fault zones is composed mainly of quartz, feldspars, calcite, chabazite and clay minerals such as illite-muscovite, kaolinite, chlorite and mixed-layer minerals such as chlorite-smectite and illite-smectite. The diagenesis and very-low-grade metamorphism of the sedimentary rock is determined by gradual changes of clay mineral ‘crystallinity’ (illite, chlorite, kaolinite), the use of a chlorite geothermometer and the reflectance of organic matter. It is concluded here that: (1) the established thermal grade is diagenesis; (2) tectonic strains affect the clay mineral ‘crystallinity’ in the fault zone; (3) there is a strong correlation between temperature determined by chlorite geothermometry and organic-matter reflectance; and (4) the duration and depth of burial as well as the pore-fluid chemistry are important factors affecting clay-mineral formation.

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High Resolution Replication of Organoclay Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100055126 ◽

1982 ◽

Vol 40 ◽

pp. 576-577

Author(s):

W. W. Barker ◽

W. E. Rigsby ◽

V. J. Hurst ◽

W. J. Humphreys

Keyword(s):

Clay Mineral ◽

Organic Molecule ◽

Organic Molecules ◽

X Ray Diffraction ◽

Xrd Pattern ◽

X Ray ◽

Naturally Occurring ◽

Silicate Layers ◽

Mineral Identification

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.

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