Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. Diversity also characterizes their chemical composition, cation exchange capacity and potassium selectivity. This review summarizes the extensive but scattered literature on halloysite, from its natural occurrence, through its crystal structure, chemical and morphological diversity, to its reactivity toward organic compounds, ions and salts, involving the various methods of differentiating halloysite from kaolinite. No unique test seems to be ideal to distinguish these 1:1 clay minerals, especially in soils. The occurrence of 2:1 phyllosilicate contaminants appears, so far, to provide the best explanation for the high charge and potassium selectivity of halloysite. Yet, hydration properties of the mineral probably play a major role in ion sorption. Clear trends seem to relate particle morphology and structural Fe. However, future work is required to understand the possible mechanisms linking chemical, morphological, hydration and charge properties of halloysite.

Halloysite clay minerals — a review

Quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols

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User's manual for WATEQ4F, with revised thermodynamic data base and text cases for calculating speciation of major, trace, and redox elements in natural waters

Critically selected values for the entropy (S°288.«), molar volume (VWw), and for the heat and Gibbs free energy of formation (AH 0 f,z98.i5 and AG°f.288.is) are given for 50 reference elements and 285 minerals and related substances. For 211 materials for which high-temperature heat-capacity or heat-content data are available AH°f,T , AG°f,T , S°T, logKf/r and (G°T H°298.i5/T) are tabulated at 100°K intervals for temperatures up to 2,000°K. For substances having solid-state phase changes or whose melting or boiling point is less than 2,000°K, we also have tabulated the properties listed above at the temperature of the phase change so that the heat or entropy changes associated with the transformation form an integral part of the high-temperature tables. INTRODUCTION The purpose of these tables is to present a critical summary of the available thermodynamic data for minerals and related substances in a convenient form for the use of earth scientists. To make the tables as useful as possible we have tried to include as much of the necessary auxiliary data as possible so that a single set of tables would suffice for most calculations, to insure internal consistency and to provide for the means of rapid revision and expansion as new data become available. This compilation is divided into two sections. In the first section we give values for the entropy (S°288.i 5 ), molar volume (V°298 . K ), the heat (enthalpy, AH°f.298.i 5 ) and Gibbs free energy (AG0 f,288. 15 ), and the logarithm of the equilibrium constant of formation (log Kf, 298.15) for the reference elements, minerals, a number of oxides, and other substances of geological interest. The data have been critically evaluated and uncertainties assigned to the 298.15°K properties. The sources of data are indicated numerically in the tables and listed in complete form following the tables. 2 THERMODYNAMIC PROPERTIES OF MINERALS The data are arranged in order of their conventional mineralogical groups. Within each group (for example the oxides) the listing is by alphabetical order of the chemical symbol of the principal cation. The tables in the second section contain values for the high-temperature thermodynamic properties, H°T H°ns.u, (G°T -H°298.iS )/T, S°T, AG°f,T, AH°,,T, and log Kf,T at 100°K intervals up to 2000°K. Heat-capacity data, as such, have been omitted from these tables in favor of the function H°T H 0 298.i 5 which is the quantity actually measured in most high-temperature experiments. Heat capacities, C P , derived from H°T H°298.i 5 data are at best only approximate and their use should be avoided when possible. Approximate values for C P are readily obtained from the first differences of the tabulated H° T H 0 298.i5 function. Thermodynamic properties of gases at high pressures have not been included in these tables. High pressure-high temperature functions of the geologically important gases H20 and C02 are given by Bain (1964), Hilsenrath and others (1955), and Robie (1966). These tables entirely supersede two earlier reports on the same subject matter by Robie (1959,1966)! ACKNOWLEDGMENTS Professor E. F. Westrum, Jr., University of Michigan, Professor 0. J. Kleppa, University of Chicago, and P. B. Barton, Jr., Priestley Toulmin, and D. R. Wones, U.S. Geological Survey, have kindly permitted us to use some of their unpublished data. We are particularly grateful to Keith Beardsley of the U.S. Geological Survey who wrote the computer routines for processing the 298.15°K tables and the bibliography. E-an Zen of the U.S. Geological Survey and Professor J. B. Thompson, Jr., of Harvard University offered many helpful suggestions for improving the clarity and usefulness of these tables. Computer facilities at the Massachusetts Institute of Technology were used initially to develop the program for compiling hightemperature thermodynamic functions. More recent revisions of the program and the present set of tables were prepared at the Harvard Computing Center, with computer costs supported by the Higgins Fund and the Committee on Experimental Geology and Geophysics of Harvard University. THERMODYNAMIC PROPERTIES OF MINERALS 3 PHYSICAL CONSTANTS AND ATOMIC WEIGHTS The symbols and constants adopted for this report are listed in table 1. Values for the physical constants used in the calculations were those recommended by the National Academy of ScienceNational Research Council (U.S. Natl. Bur. Standards Tech. News Bull., v. 47, p. 175-177, 1963). For convenience we also give values of the international atomic weights for 1963 (scale C12 = 12.0000) in alphabetical order by their chemical symbol in table 2. Elements for which no atomic weight is listed have no stable isotope. TABLE 1. Symbols and constants T Temperature in degrees Kelvin, (°K) gfw Gram formula weight H° -H° Enthalpy at temperature T relative to 298.15°K in cal gfw 1 , T S° Entropy at temperature T in cal deg-gfw" 1 G° -H° T SM.15 m Gibbs free energy function in cal deg-gfw" 1 A^f° Heat of formation from reference state in cal gfw" 1 AG° Gibbs free energy of formation from reference state in cal gfw"1 Kr Equilibrium constant of formation Cp Heat capacity at constant pressure in cal deg-gfw" 1 0 Superscript indicates the substance is in its standard state » TTO meit Heat of melting at one atmosphere in cal gfw" 1 AH° Heat of vaporization to ideal gas at one atmosphere at the "p normal boiling point in cal gfw" 1 V° Volume of one gram formula weight at one atmosphere and "* " 298.15°K in cm8 R Gas constant, 1.98717 ±.00030 cal deg-gfw 1 , 8.31469 joules deg-gfw" 1 cal Calorie, unit of energy, 4.1840 absolute joules, 41.2929 cm* atmosphere A Avogadro's number, (6.02252 ±. 00028) xlO23 formula ' units gfw1 P Pressure, either in atmosphere or bars atm Atmosphere, 1,013,260 dynes cm"* bar Bar, 1,000,000 dynes cm"2 log Common logarithm, base 10 In Natural logarithm, base e= 2.71828. . . THERMODYNAMIC PROPERTIES OF MINERALS TABLE 2. Atomic weights for 1963

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Thermodynamic properties of minerals and related substances at 298.15 K (25.0 C) and one atmosphere (1.013 bars) pressure and at higher temperatures

Organic compounds can interact with clay minerals by i) adsorption at the external surfaces, ii) adsorption at the external and internal surfaces, iii) by exchange of exchangeable ions at the external surfaces, iv) by exchange of exchangeable ions at the external and internal surfaces, and v) by grafting reactions with silanol and aluminol groups leading to covalent bonds. Kaolin minerals intercalate only are a limited number of compounds whereas the reactions of 2:1 clay minerals, in particular smectites and vermiculites, are very manifold. Special attention is given to the interaction with neutral organic molecules such as alcohols, fatty acids, amines, amino acids, aromatic compounds, macrocyclic compounds, and nuclein bases. The interaction with complexes and dyes also provides the basis of advanced applications of clay minerals. Binding of long chain alkylammonium ions is a fundamental reaction for hydrophobising clay mineral particles as needed in many applications. The interaction of clay minerals with polymers including proteins is not only an actual field of research but also of practical importance. Organo-clay minerals are used as effective adsorbents. As these materials also adsorb solvent molecules together with the adsorptive, the adsorption process must be considered as adsorption from binary solution which, therefore, is also described in this chapter.

Clay mineral-organic interactions

The origin of Missouri fire clays is interpreted from the testimony of the clays in terms of the geologic setting in which they were deposited and developed. Hence, the approach to the interpretation is fundamentally that of sedimentary petrology, rather than economic geology. The clays, as sedimentary rocks, are considered to be the products (mineralogic and geologic) resulting from the responses of their source materials to the energetics of the physical and chemical environments which were impressed upon them during the time interval of their deposition and diagenesis. The fire clays are inferred to have a sedimentary origin; it is believed that their present-day characteristics were essentially developed in the time intervals of the Cheltenham to pre-Fort Scott (Pennsylvanian) age. The different varieties of fire clay are interpreted as different lithofacies within a continuous Cheltenham deposit. The high-alumina facies (diaspore-burley and boehmite) appears to have been formed by severe leaching on a relatively stable land area, whereas the kaolinitic-illitic facies (semi-plastic to semi-flint clay) seem to characterize products formed near the margin of a slowly sinking depositional region. Both processes of destruction and construction (“katamorphism” and “anamorphism,” as used by Van Hise, 1904) appear to have operated in the genesis of the clay minerals. Evidence points toward a negative Eh and an approximately neutral to slightly acid pH during the formation of the clays. The presence of diaspore and boehmite and the absence of gibbsite in the high-alumina clay are interpreted as indications of leaching of clay minerals under waterlogged conditions. Diaspore may inherit part of the crystal structure and energy of the kaolinite from which it was derived.

The Origin of Missouri Fire Clays

Flint clay is denned as a sedimentary, microcrystalline to crystalline clay (rock) composed dominantly of kaolin, which breaks with a pronounced conchoidal fracture and resists slaking in water Additional ceramic (refractory) properties are implied, but not expressed, in the definition Flint clay first given recognition in the USA, has been observed on all continents; it will probably be found to be more abundant than its occurrences reported to date It occurs in rocks mainly Carboniferous or Cretaceous in age, and is invariably associated with plant- or coal-bearing measures The environment of deposition is commonly lowlying paludal, in basins in either clastic silicate rocks or in karstic carbonates It is inferred that parent illitic and/or kaolinitic clay colloids were transported into the swamps and there under-went further dialysis, alteration, and eventual crystallization in situ, producing a notably homogeneous kaolinite clay possessing interlocking crystallinity Some occurrences were further desilicated to high-alumina minerals, particularly to diaspore and boehmite Flint clay is interpreted as being an intermediate member of a so-called flint-clay facies which is a claystone sequence ranging from high-alumina minerals (or potentially so) formed on the highest part, structurally and/or topographically, of the depositional area, and grading down-structure and/or lower in elevation through flint clay to iliite-kaolinite plastic clay and thence to marine illitic shale, all being equivalent stratigraphically The geochemical reactions are depotassification of parent clay by substitution of K+ by H+, and desilication, especially where high-alumina minerals are formed

Flint Clay and a Flint-Clay Facies

Aqueous solubility studies of high-alumina and clay minerals

The dissolved major ions and amount of suspended sediment were determined in five glacial milks from the United States, seven from the Alps, three from Norway, and meltwater from two glaciers in the Antarctic. Highest dissolved silica, 8 ppm Si, was found in Emmons and Nisqually glacial milk, Mt. Rainier, where the country rock is largely andesitic volcanic. Lowest silica, .42 ppm, was determined in glacial milk from granite in Norway. Highest dissolved Ca, 26.6 ppm, and Mg, 7.6 ppm, were determined from Diablerets and Trient (Alps) milk respectively, from limestone terrain, but milk from greenstone, ophiolite, and diabase at Zermatt (Alps) is also high in Ca and Mg. Highest K, 1.72 ppm, was determined from Chamonix (Alps) glacial milk from granitic rock, but K was also high in milk from Mt. Rainier andesite. Highest Na, 3.05 ppm, and P, 1.54 ppm, were found in Emmons and Nisqually milk. Composition of country rock, and the rock9s susceptibility to hydrolysis and solution control the dissolved load of glacial milk. The pH values of all glacial milks were 6.4–7.5 except those from Norway (4.1–4.5). The pH of rock slurries, made by pulverizing under water in the laboratory rocks from the moraines of the glaciers, ranged from 8.2 to 9.8 and correlated with abrasion pH of their constituent minerals. The pH of the slurries ran higher than the pH of corresponding glacial waters. Dissolved constituents in rock slurries were commonly higher in concentration than those in glacial milks: Si was commonly 4–6 times higher; Ca, 2 times; Mg, 2–15 times; K, 20–40 times; and Na, 10–20 times. Concentration of dissolved Si tends to increase with concentration of Na and K, but decreases with Ca and Mg. Factors effective in rock dissolution are rock texture, composition, pH of hydrolysate, and exposure to CO 2 . The amount of suspended matter in glacial melt-water is controlled by the character of the rock eroded, glacial abrasion, and glacial melting. Emmons’ milk carried approximately 7100 ppm solids; Grinnell, Chamonix, and a milk from Norway, approximately 5 ppm. Electron micrographs are presented. Glacial milk is a valuable contributor to sustaining fertility of soil because dissolved elements are immediately available to plants and ion-exchange complexes in the soil, and rock flour releases ions moderately readily because of its high specific surface area.

Glacial Milks and Their Laboratory-Simulated Counterparts

The 16-8-, 8-5-, 5-2-, 2-1-, 1-0.5-, 0.5-0.3-, 0.3-0.1-, and <0.1-μm size fractions were centrifuged from a Georgia (U.S.A.) sedimentary kaolin and a hydrothermal kaolin from the Sasso mine (Italy) and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TGA) together with the corresponding whole rocks. All size fractions of the Georgia sample consisted dominantly of well-crystallized, fine-grained kaolinite, associated with minor quantities of smectite. Some halloysite-like elongate particles were noted by SEM in the intermediate size fractions, minor amounts of quartz were identified in the coarsest size fractions, and < 1% noncrystalline material and traces of organic material were suspected in the finest size fraction. The crystallinity of the kaolinite as measured by XRD and IR varied moderately with size. IR suggested that nacrite-like stacking disorder increased with decreasing size for particles < 5 μm in size.

Walter D. Keller

Papers

The Origin of Missouri Fire Clays

Flint Clay and a Flint-Clay Facies

Aqueous solubility studies of high-alumina and clay minerals

Glacial Milks and Their Laboratory-Simulated Counterparts

Compositional and structural variations in the size fractions of a sedimentary and a hydrothermal kaolin