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Mixed-Layer Kaolinite—Montmorillonite from the Yucatan Peninsula, Mexico

Published online by Cambridge University Press:  01 July 2024

L. G. Schultz ,
A. O. Shepard ,
P. D. Blackmon  and
H. C. Starkey
L. G. Schultz
Affiliation:
U.S. Geological Survey, Denver, Colorado 80225, U.S.A.
A. O. Shepard
Affiliation:
U.S. Geological Survey, Denver, Colorado 80225, U.S.A.
P. D. Blackmon
Affiliation:
U.S. Geological Survey, Denver, Colorado 80225, U.S.A.
H. C. Starkey
Affiliation:
U.S. Geological Survey, Denver, Colorado 80225, U.S.A.
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Abstract

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Clay beds 1–2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe1·03+Mg0·5)(Al0·75Si7.25)O20+(OH)4−, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1/10 to 1/20 μ across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 Å after heating at 300°C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins.

Résumé

Résumé

Les couches d’argile de 1 à 2 m d’épaisseur alternant avec des calcaires marins datant probablement du début de l’éocène, sont composées d’un interstratifié kaolinite-montmorillonite à peu près pur. L’étude de la taille des particules, les micrographies électroniques, la diffraction des rayons X, les analyses chimiques, les expériences d’échange de cations, l’ATD et l’ATG, indiquent que les argiles provenant de trois localités différentes contiennent en proportion à peu près égale des feuillets de kaolinite et de montmorillonite interstratifiés au hasard. La montmorillonite a en moyenne la formule structurale K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe1·03+Mg0·5)(Al0·75Si7·25)O20+(OH)4−, avec un déficit d’OH de structure aussi bien dans les feuillets de montmorillonite que de kaolinite. Du potassium non échangeable indique que quelques feuillets sont du type mica. Les cristaux sont le plus souvent des plaques arrondies d’un diamètre allant de 1/10 à 1/20 μ. Le diagnostic essentiel du caractère interstratifié est un pic de diffraction X voisin de 8 Å après chauffage à 300°C. On suppose que les argiles se sont développées par altération d’une cendre volcanique, suivie d’une érosion et d’un dépôt dans des bassins protégés voisins de la côte.

Kurzreferat

Kurzreferat

Tonbetten von 1–2 m Stärke und zwischengelagert mit Meerkalkstein aus dem frühen Eozän setzen sich aus fast reinem gemischtschichtigem Kaolinit-Montmorillonit zusammen. Untersuchungen der Teilchengrösse, Elektronenmikrographien, Röntgenbeugungsuntersuchungen, chemische Analysen, Kationenaustauschversuche, DTA und TGA deuten darauf hin, dass Tone von drei verschiedenen Fundorten ungefähr gleiche Anteile unregelmässig zwischengelagerter Kaolinitund Montmorillonitschichten enthalten. Die Montmorillonitstrukturformeln umfassen im Durchschnitt K0,2Na0,2Ca0,2Mg0,2(Al2,5Fe1,03+Mg0,5)(Al0,75Si7,25)O20+(OH)4−, mit einem Mangel an strukturellem (OH) in entweder den Montmorillonitoder den Kaolinitschichten. Nichtaustauschbare K+ zeigen an, dass einige Schichten glimmerähnlich sind. Die Kristalle sind meist runde Plättchen von 1/10 bis 1/20/ μ Quermass. Das eindeutigste Merkmal des Gemischtschichtcharakters ist eine Röntgenreflexion nahe 8 Å nach Erwärmung auf 300°C. Es wird vermutet, dass sich die Tone durch Verwitterung vulkanischer Asche und nachfolgender Erosion und Ablagerung in geschützten, küstennahen Bassins gebildet haben.

Резюме

Резюме

Глинистые пласты мощностью 1–2 м, переслаивающиеся с морским известняком, возможно, раннеэоценового возраста, состоят из почти чистого смешанно-слойного каолинит-монтмориллонита. Изучение размеров частиц, данные электронной микроскопии, рентгено-графии, химического анализа, изучение катионообменных свойств, ДТА и ТГА показали, что глинистый минерал трех различных месторождений содержит примерно равные доли бес-порядочно чередующихся каолинитовых и монтмориллонитовых слоев. Усредненная структурная формула монтмориллонита: K0,2Na0,2Ca0,2Mg0,2(Al2,5Fe1,03+Mg0,5)(Al0,75Si7,25)O20+(OH)4−; характерен дефицит структурных гидроксилов как в монтмориллонитовых, так и в каолини-товых слоях. Наличие необменных ионов К+ указывает на слюдяную природу некоторых слоев. Кристаллы в большинстве случаев представляют округлые пластинки с диаметром 1/10–1/20 мк. Наиболее вероятным диагностическим признаком смешанно-слойного характера минарала является рентгеновское отражение около 8 Å образцов, нагретых до 300°. Эти глины образовались при выветривании вулканического пепла с последующим переотложением в околобереговых бассейнах.

Type
Research Article
Information
Clays and Clay Minerals , Volume 19 , Issue 3 , July 1971 , pp. 137 - 150
Copyright
Copyright © Pergamon Press 1971

Footnotes

*

Publication authorized by the Director, U.S. Geological Survey.

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