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SHROCK, Consulting Editor CLAY MINERALOGY Mc Graw-Hill Series in the Geological Sciences ROBERT R. More recently a very great interest in clay mineralogy has developed in Great Britain. 94 Glaesser, R., On the Mechanism of Formation of Montmorillonite-Acetone Com- plexes, Compt. The later phases developed at higher temperatures are dependent primarily on bulk composition, and here "inheritance" is of little importance.SHROCK, Consulting Editor DE SITTER Structural Geology EWING, JARDETZKY, AND PRESS Elastic Waves in Layered Media GRIM Clay Mineralogy HEINRICH Microscopic Petrography SHROCK AND TWENHOFEL Principles of Invertebrate Paleontology CLAY MINERALOGY RALPH E. Mac Ewan 100 of the Rothampsted Agricultural Experi- ment Station has studied in detail the reaction of the clay minerals and organic compounds. Thus in the case of the develop- ment of mullite or cordierite, the controlling factor is probably the amount of magnesium present.GRIM Research Professor of Geology University of Illinois New York Toronto London Mc GRAW-HILL BOOK COMPANY, INC. This book, or parts thereof, may not be reproduced in any form without permission of the publishers. He has presented the analyses of many soil mate- rials 101 and has contributed to X-ray techniques 102 and the structure of 91 Mering, J., Reactions des montmorillonit, Bull. The spinel-forming specimens all develop more or less cristobalite around 1000 or 1100C without going through the quartz intermediate stage.1953 CLAY MINERALOGY Copyright, 1953, by the Mc Graw-Hill Book Company, Inc. Library of Congress Catalog Card Nwriber: 52-13807 IV THE MAPLE PRESS COMPANY, YORK, PA. No separate features appear in the differential thermal curves to indicate any energy effect associated with the growth of the cristobalite.PREFACE The present volume attempts to summarize available data on the structure, composition, properties, occurrence, and mode of origin of the various clay minerals whose identities have been reasonably well estab- lished. Chemical Analyses INDEX 375 CHAPTER 1 Introduction DEFINITIONS Clay is used as a rock term and also as a particle-size term in the mechanical analysis of sedimentary rocks, soils, etc. Since this is true also of opal fired alone, it is assumed that any exchange involved is not picked up by the thermal method.The distribution of the clay minerals in rocks of various litho- logic types, geologic age, and condition of formation is considered, and an attempt is made to analyze the environmental conditions under which the individual clay-mineral groups are formed and are stable. As a rock term it is difficult to define precisely, because of the wide variety of materials that have been called clays. Favejee, On the Crystal Structure of Montmoril- lonite and Halloysite, Z. Cristobalite is actually effectively somewhat less dense than the condensed-layer con- Dehydration 227 figuration derived from the articulation of the silica layers (see page 228) and might even require an energy input under the conditions of the analyses.Because of the scantiness of available data, the general conclusions resulting from such analyses must be considered as tentative and preliminary. In general the term clay implies a natural, earthy, fine-grained material which develops plasticity when mixed with a limited amount of water. Mehmel, Ueber den optischen und rdntgenographischen Nachweis von Kaolinit, Halloysit, und Montmorillonit, Z. 78 Mehmel, M., Ueber die Struktur von Halloysit und Metahalloysit, Z. Concepts of the Composition of Clay Materials 23 clearly the two forms of halloysite and to show their relations to each other. The spinel tends to disappear at temperatures above about 1200C in all samples studied except the nontronite sample.

Generally such minerals have not been classed with the clay minerals, and their structure, properties, occurrence, and modes of origin have already been reported in detail in monographic form in the literature. Discussion of weathering products formed from various types of rock under varying conditions. The difficulty is that some material called clay does not meet all the above specifications. At Hanover in Germany, Noll 81 began about 1933 the study of the laboratory synthesis of the clay minerals and produced the best data yet available on this subject. Rather, it is merely an irregularly constituted assemblage of small cations, some octahedrally coordinated and others tetrahedrally coordinated, with only the oxygen packing actually approaching crystalline regularity.The specific properties of the individual clay minerals are discussed, but no attempt is made to consider the larger rock properties of clay materials except incidentally as they are related to specific mineral properties. Thus, so-called flint clay has substantially no plasticity when mixed with water. Wilm, R6ntgenographische und kolloidchemische Untersuchungen fiber Ton, Angew. In the Netherlands at the Agricultural College in Wageningen, Edel- man and his colleagues 82 began an active study of clay mineralogy in the early 1930's. The spinels grow rapidly to a clearly crystalline powder affording a clean diffraction diagram.For example, the changes taking place when the individual clay minerals are heated are discussed at some length, and the relation to the refractoriness of clays is indicated. It does, however, have the other attributes of clay. It is used for material that is the product of weathering, has formed by hydrothermal action, or has been deposited as a sediment. They developed a structural concept 88 of montmorillonite and halloysite, somewhat different from that suggested by Hofmann et a7., 75 which still claims considerable attention. No noticeable difference in relative intensities is observed between the diffuse and the sharp patterns, although cube-edge parameters may change somewhat (with changing composition), and no erratic appearance of new lines has been observed.A detailed discussion of the refractoriness of clays, which is influenced by other factors than the clay- mineral composition, is not, however, included. As a particle-size term, the clay fraction is that size fraction composed of the smallest particles. Wilm, Kristallstruktur und Quellung von Mont- mori Uonit, Z. They 84 also determined the clay-mineral compostion of many types of soil. H., Relation between the Crystal Structure of Minerals and Their Base-Exchange Capacity, Trans. The cryptocrystalline quartz produced on firing many montmoril- lonites at about 1000C exhibits many vagaries with respect to its apparent relation to high-low inversion.The clay minerals are the major factor controlling the larger rock properties of clay materials, such as plasticity, strength, sensitivity, etc. The maximum size of particles in the clay size grade is defined differently in different disciplines. In 1927, Orcel 85 in Paris first applied the differential thermal procedure in its modern form to the study of clay minerals, and its general use today is due in no small part to Orcel's efforts. Synthesized quartz, when observed by Bradley and Grim at room temperature, was found in some cases as the a, in others as the ft modification, and in one case apparently intermediate.Other factors also influence these properties, and an adequate discussion of them would require the presentation of much additional fundamental data. Sepiolite, attapulgite, palygorskite 13., OBIGIN AND OCCUBBBNCB or THE CLAY MINEBALS 316 Synthesis of the Clay Minerals 316 Introduction. In geology the tendency has been to follow the Wentworth 1 scale and to define the clay grade as material finer than about 4 microns. Swineford, Morphology and Structure of Endellite and Halloysite, Am. In association with Orcel 86 at first and later independently, Henin and Caillere 87 have actively pursued a variety of clay-mineral investigations. Both the a and ft forms make the normal slow transition to cristobalite at more elevated temperatures.

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