Differential settling velocities of individual clay mineral types and clay mineral mixtures in quiet saline water are reported for ocean water chlorinity range 0–18‰, brackish water ionic strength range 0.0–0.686 moles-(unit charge)2/kg, temperature range 6–26°C, clay mineral concentration range 0.01–3.6 g/1., and pH range 6.5–9.8. The materials employed included natural deposit clay minerals and clay minerals extracted from marine sedimentary matter and from terrestrial soils.

Settling velocities at 26°C for illitic and kaolinitic materials reached values of 15.8 and 11.8 m/day, respectively, at an ocean water chlorinity of 18‰ and exhibited little dependence upon chlorinity above a chlorinity of 2‰. Settling velocities for montmorillonites were found to be functions of chlorinity over the entire chlorinity range 0–18‰ and to increase exponentially to a limit of 1.3 m/day at 26°C. The settling velocities were determined by pipette analysis, Oden balance techniques, Kelley-Wiegner manometer methods, and spectrophotometric methods, using artificial sea-water and filtered Gulf of Mexico water.

In quiet brackish water, variations in ionic ratio composition alter the settling rates of illites and kaolinites less than 15 percent from such rates in ocean water, at constant, brackish water, ionic strength of 14 or greater. In contrast, montmorillonitic settling rates in such water varied by 40 percent or more from ocean water rates, at constant ionic strength unless the magnesium—potassium or magnesiun-strontium ionic ratios of the brackish water were kept constant. These induced variations were not sufficient in magnitude, however, to change the general relative order of settling rates for the clay minerals.

Decreasing temperatures over the range 26°-6°C decreased settling rates (of all clay types) progressively up to about 40 percent in accordance with temperature-induced changes in the viscosity and density of the saline water medium.

The influences of fifty-seven different organic compounds or materials (carbohydrates and proteins dissolved or dispersed in the water) upon the settling velocities are cited. In general, carbohydrates increased the settling rates of montmorillonitic materials as much as 25 percent, and proteins decreased such rates a maximum of 1–5 percent. Kaolinitic materials suffered a 30–40 percent decrease in settling velocity under the influence of some proteins. So-called “humic acids,” derived from quinone and soil fractions, decreased kaolinitic and montmorillonitic settling rates to lesser extent. No significant alterations of illitic settling rates by organic materials were noted.

Chlorite-montmorillonites were found to settle slightly faster than sodium and calcium montmorillonites. Potassium-saturated montmorillonites settled from two to three times as rapidly as the reference montmorillonites. Chlorite settling rates, of magnitude comparable to rates found for kaolinites, and vermiculite settling rates, comparable at higher chlorinities to illite settling rates, are also reported.

The apparent interaction of illite and montmorillonite to form illitic-montmorillonitic settling entities in some clay mineral mixtures was noted. Other mixtures, exposed to artificial sea-water for 3–6 years, exhibited a tendency to transport 5–20 percent kaolinite within a developed illitic-chloritic mix, when reagitated.

Evidence is also presented to support the argument that clay minerals do not settle in single solid particulate units in saline waters. The effective settling unit, after flocculation, is described as a coacervate, i.e. as a thermodynamically reversible assembly of solid clay particles or strands within a settling solid-rich liquid unit phase. Settling rate increases are thereby not a consequence of any irreversible formation of larger solid particles or solid aggregates by coalescence of fresh water particles at or beyond the fresh-water-saline-water interface.

Differential transport of clay minerals by the turbulent flow of saline water in a pipe is quantitatively described. Flow rates of about 6 miles/hr were required to eliminate differential transport of the clay minerals. Clay mineral concentrations over the range 0.01–15.0 g/l. were considered.

Chemical data, electron and x-ray diffraction data, base exchange data, and electron micrographs support the settling velocity information.

Samples of a montmorillonite, a mixed-layer mineral (mica and montmorillonite) “illite”, kaolinite, and halloysite were immersed in 50 ml sea-water for 10 days, and additional samples of the first three were immersed for 150 days. The exchangeable cations were determined both before and after treatment. It was found that Mg2+ ions from sea-water moved into the exchange positions in the minerals in preference to Ca2+ and Na+ ions. The H-form of these minerals showed a gradual adjustment to sea-water as measured by change in pH and filling of the exchange positions with cations other than H+. Kaolinite adjusted very rapidly, but montmorillonite and the mixed-layer mineral were slow. All the minerals reacted to yield appreciable amounts of SiO2, Al2O3, and Fe2O3 to the sea-water. The quantities yielded are in the order:

montmorillonite > mixed-layer mineral > “illite” > kaolinite > halloysite The solubility is considered to be due to direct solution of SiO2 in the sea-water and to removal of Al2O3 from the octahedral layer of the minerals.

When H-clays were titrated with sea-water three distinct kinds of curves were obtained: (a) kaolinite; (b) mixed-layer mineral, “illite,” and halloysite; and (c) montmorillonite. The curves are similar to those obtained with clay minerals titrated with other alkaline solutions. Kaolinite reacts somewhat like a number of simple acids, but the curves for the other minerals are more complex and are related to the neutralization of H and its replacement in the exchange sites by metallic cations. The exchangeable cations were determined in the minerals after titration, and the results are similar to those obtained after immersing the minerals in sea-water. The volume of sea-water required to reach an end point at about pH 7.6 varies from 11 ml for kaolinite to 135 ml for montmorillonite and is related to the titratable alkalinity of the sea water and to the exchange capacity of the minerals.

Differential dissolution in NaOH solution was investigated as a means of purification of clay. It was discovered that a large quantity of allophane and free alumina and silica were dissolved from clay preparations in 0.5 N NaOH solution by boiling for as little as 2.5 min, provided the ratio of clay weight to solution volume was kept less than 100 mg to 100 ml. Reprecipitation of dissolved silica occurred if a more prolonged digestion or higher sample to solution ratio was employed. Also, prolonged digestion in the NaOH solution (for 80 min) dissolved as much as 50 percent of kaolinite (Merck) and 25 percent of Wyoming montmorillonite, but only a small quantity of these crystalline minerals was dissolved during the 2.5 min digestion period. Subsequent dithionite-citrate-bicarbonate treatment removed the released iron. Marked improvement of x-ray diffraction patterns of the clays resulted. This rapid and selective dissolution of allophane and free oxides greatly improves the quantitative analysis of crystalline minerals by conventional methods.

After dehydroxylation at 500°C, kaolinite and halloysite became amorphous and also dissolved by the same differential dissolution procedure. Heat-stable (aluminous) montmorillonite and chlorite were only slightly dissolved by this treatment. The selective removal of the 1 : 1 layer aluminosilicates greatly improves the quantitative analysis of the remaining crystalline components of clays by conventional methods.

Chlorite-like complexes of montmorillonite with magnesium hydroxide or aluminum hydroxide have been prepared under a variety of physical and chemical conditions. Requirements for the preparation of these complexes have been simplified considerably by the use of rapid mixing techniques. A complex may be formed either by precipitating the hydroxide in a clay suspension or by preparing the precipitate separately and mixing it immediately with the clay suspension. It is suggested that the process involves the adsorption of a layer of the precipitate over the entire surface of the montmorillonite unit layer rather than the direct formation of a structure in the interlayer space. It is considered that there is no appreciable permanent association of unit 10 Å layers of montmorillonite in a well stirred suspension, even in the presence of strong salt solution, but that instead most clay surfaces are exposed continually. The chlorite-like structure develops only upon association of the unit layers through aging or dehydration.

The aluminum hydroxide complex with montmorillonite differs somewhat from the magnesium type, but it has the approximate chlorite basal spacing. The complex shows a second-order basal diffraction spacing of low intensity, and forms regular expanded structures with water or ethylene glycol. A gibbsite structure for the interlayer material is most compatible with the x-ray data.

The occurrence of this process in sediments and soils is considered to be very probable, although it is premature to consider precise environments until more experimental data are available.

Heat treatment at 600°C has been the usual procedure for irreversible collapse of expanding clay minerals prior to determination of the external surface area of clays and soils by glycerol retention. Evidence is presented showing that this treatment is unsuitable since it greatly reduces the external surface area of certain minerals and increases that of others. Saturation with the triethylammonium cation avoids these difficulties and produces an effect analogous to the collapse of expanding minerals by stabilizing their basal spacing at 13.3 Å. This prevents the entrance of glycerol between the unit layers and confines the sorption to the external surfaces of the particles.

Bottom sediment clay mineral assemblages from the Rappahannock River and estuary contain kaolinite, illite, unorganized illite, dioctahedral vermiculite, 12.4Å montmorillonite, 14.2 Å montmorillonite, chlorite, feldspar and quartz. The x-ray diffraction characteristics of these species and their thermal modifications at 25–500°C are described and illustrated. Progressive changes in the mineralogical composition of bottom sediments occur between the fresh-water and saline-water portions of the Rappahannock system. Chlorite and feldspar occur exclusively in the saline portions of the estuary. Illite shows progressive increase in crystallization quality. There appears to be less kaolinite, proportionately, in the estuarine sediments of the most saline zone. x-Ray diffraction diagrams showing these progressive changes are illustrated.

The basal Cretaceous beds of the area are subdivided into three units: the Cape Fear formation, Middendorf formation and Bladen member of the Black Creek formation. Stratigraphic position and lithology indicate that the Cape Fear is the oldest and the Middendorf is in part the landward facies of the Bladen. The Middendorf sediments are fluviatile and the Cape Fear and Bladen sediments are probably marine.

The Cape Fear and Bladen contain abundant montmorillonite, some kaolinite and lesser amounts of illite. In the Middendorf kaolinite predominates, although a few samples have small amounts of montmorillonite and illite.

Preliminary data indicate that in the Cretaceous-Tertiary sediments of the Atlantic Coastal Plain, montmorillonite occurs in abundance in the marine beds and kaolinite in the nonmarine sediments. The basal Cretaceous beds of the area studied fit into this scheme of clay mineral distribution.

The origin of the clay minerals of the Cretaceous formations studied is approached from sedimentary and empirical standpoints. The montmorillonite-marine and kaolinite-nonmarine associations strongly suggest that the montmorillonite has formed by marine diegenesis, whereas the sedimentary evidence suggests that the montmorillonite of the Cape Fear formation is detrital and the kaolinite of the Middendorf formation has formed by prolonged postdepositional weathering of a more varied clay mineral assemblage. The sediments of the Bladen unit in themselves offer little evidence as to the origin of their clay minerals. However, the predominance of kaolinite in the contemporary deltaic Bladen suggest that kaolinite was the only clay mineral supplied to the depositional area, and that in the marine part of the sedimentation area part of this kaolinite was changed to montmorillonite by marine diagnetic processes.

A semiquantitative study of the surficial clay mineral distribution from 79 cores in the Recent sediments in the Gulf of Mexico shows a regional pattern which can be related to source and environment. The dominant factor controlling distribution of these surflcial sediments appears to be source. Montmorillonite is the most abundant clay mineral, and illite, chlorite, kaolinite and mixed-layer minerals are present in almost every sample.

Alteration of the clay minerals is influenced by (a) change of environment, and (b) length of exposure. Initial ion exchange, which is caused by a tendency to reach equilibrium with a new environment, occurs so rapidly in the clay minerals after they enter the marine environment that rate of sedimentation is a minor factor in comparison to environmental change. Slow alteration and adjustment toward a stable end state are most complete in areas of slow deposition and extended exposure of the clay minerals to the environment.

THE Olive Hill fire clay bed of Crider (1913) is the principal source of the raw material used in the refractory industry of eastern Kentucky. The bed is a discontinuous underclay from 1 to 20 ft above a prominent unconformity which separates Mississippian and Pennsylvanian rocks. Upper Mississippian rocks consist of ten marine limestone and shale units all truncated by the unconformity. Pennsylvanian rocks are chiefly: (a) massive deltaic sandstone; (b) cut-and-fill deposits of shale, siltstone and sandstone which contain several beds of coal and underclay including the Olive Hill fire clay of Crider (1913); and (c) dark-gray shale beds.

The Olive Hill fire clay of Crider consists of approximately one-third flint clay, two-thirds semiflint clay, and minor amounts of plastic clay. The clay mineral content ranges from nearly pure kaolinite to kaolinitic clay containing about 40 percent illite and mixed-layer clay. The kaolinite ranges from highly crystalline to very poorly crystalline “fireclay” kaolinite. The degree of crystallinity of the kaolinite and hardness of the clay vary inversely with the amount of illite and mixed-layer clay present. The nearly pure kaolinite is believed to have formed by removal of silica and alkalies from mixtures of kaolinite, illite and mixed-layer clay by leaching shortly after deposition.

An isopach map shows that Crider’s Olive Hill fire clay occurs in irregular, lens-shaped deposits. Fossil plant rootstocks with rootlets attached in the clay clearly indicate it supported plant growth. The overlying coal and presence of some organic material in the clay suggest that the Olive Hill fire clay was deposited under a reducing environment in swamps.

Gypsum deposits of Mississippian age in southwestern Indiana contain several argillaceous partings. A study of these partings was made to find out what clay minerals are present in such an evaporite association.

The most abundant minerals in the clay partings are dolomite, gypsum, quartz, illite, chlorite and mixed-layer illite-montmorillonite. No kaolinite was found in any of the samples.

Radiocarbon dates indicate that the maximum time of weathering for soils of the Tazewell substage may be about 6400 years longer than that available for weathering of soils of the Cary substage.

Detailed mineralogical and chemical studies were made of the 2–0.2 μ fractions of 0–6 in. and 30–36 in. samples from 24 sites along a traverse extending from the Cary substage across the Tazewell substage in east-central Indiana. The major clay mineral constituents of the 0–6 in. samples were illite and 14 Å material; illite and montmoril-lonite were the main components in the 30–36 in. samples. The correlation coefficients between illite content and percentage K2O for the 0–6 in. and 30–36 in. samples were 0.85 and 0.92, respectively.

The end and terminal moraines of the Tazewell substage were found to have a higher illite content than the ground moraines. This was attributed to superglacial movement and enrichment of foreign materials, i.e. mica schists from the Canadian shield, on end and terminal moraines.

The results of saturation of the clay fraction with potassium and magnesium on the proportion of 10Å, 12.7Å and 14Å spacings indicated that weathering had lowered the surface charge density of the micaceous minerals in the 0–6 in. samples to a greater extent than in the 30–36 in. samples. This effect, in addition to other weathering reactions, resulted in partially expanded micaceous minerals in the 0–6 in. samples which were much more resistant to collapse than were the minerals in the 30–36 in. samples.

The rate of weathering of K2O from the 2–0.2μ fraction of the 0–6 in. samples located on ground moraines was estimated to be about 0.1 percent per 1000 years. This value was used in estimating the ages of the morainie systems of the Tazewell in Indiana. The estimated ages were as follows: Mississinewa, (radiocarbon date) 13,140 years; Union City, 14,500 years; Bloomington, 15,500 years; Champaign, 18,700 years; Shelbyville, (radiocarbon date) 19,500 years.

The fertility status of the soils on the Tazewell has been influenced appreciably by the length of the weathering period, the potassium-supplying power of the soils decreasing with increasing age.

x-ray diffraction traces were made of oriented aggregates of artificial binary mixtures containing approximately equal, weighed amounts of samples of illite, montmorillonite, mixed-layered combinations of illite and montmorillonite, and of kaolinite samples having different degrees of crystallinity. Measurements most suitable for quantitative purposes were obtained from the 7 Å kaolinite peaks and from the 10 Å peaks of illite and collapsed montmorillonite and collapsed mixed-layer clay. In this paper the sum of five height measurements at half-degree intervals across the peak are considered to be a measure of the area of the peak. Fireclay-type kaolinites gave 7 Å peak areas about equal to the area of the 10 Å peak of an equal amount of illite, montmorillonite, or mixed-layer clay, whereas well-crystallized kaolinites gave 7 Å peak areas generally about twice that of the 10 Å peak of an equal weight of the illite-montmorillonite minerals. Kaolinite samples having intermediate degrees of crystallinity gave 7 Å/10 Å peak area ratios intermediate between 1: 1 and 2:1. The shape of the 7 Å kaolinite peak was used to evaluate the crystallinity of the kaolinite.

x-ray diffraction characteristics of the chlorite minerals from the different groups of sedimentary rocks studied vary considerably, and no uniform method has been found for their evaluation.

Since the publication of the paper on the minerals of the montmorillonite group by Ross and Hendricks (1945) some species have been added to the group, and minor changes in the acceptable species have become advisable. No radical changes are proposed, but a review of the members and their grouping will be presented. The acceptable dioctahedral members of the group appear to be montmorillonite, nontronite and volchonskoite. Beidellite should be discontinued. The acceptable trioetahedral members of the group appear to include saponite, hectorite, sauconite, stevensite and medmontite. Griffithite is probably a useful term for an iron-rich saponite. Representative chemical analyses and formulas have been assembled to illustrate relationships.

The introduction of counter tubes and the related instrument geometries have made it possible to obtain greatly improved x-ray powder patterns. Most of the important factors that must be understood in x-ray diffractometry are described in terms of their effect on the intensity, peak-to-background ratio, resolution and line shape. These factors are the geometry of the x-ray optical system, the x-ray tube focal spot size, the angular apertures of the primary beam in the focusing and axial planes, the 2 : 1 setting, and the receiving slit. The precision is often limited by the specimen preparation rather than the instrument, and the effects of homogeneity, displacement and transparency, crystallite sizes, and preferred orientation are outlined. A new diffractometer arrangement employing a transmission specimen followed by a focusing crystal monochromator is shown to be a useful supplement to the standard reflecting specimen diffractometer for clay mineral studies. The important characteristics of Geiger, proportional and scintillation counters are described in terms of linearity, quantum counting efficiency, pulse amplitude distribution and counting statistics. A bibliography of key literature references is appended.

Selected chemical and diffraction analyses from the literature, supplemented by thermal and thermogravimetric analyses and infrared absorption observations, are utilized to construct a rational model of the water arrangement in natural vermiculites.

A super cell is arranged by simple modification of the Hendricks water nets to accommodate the somewhat higher water contents, indicated by weight loss analyses, and the exchangeable cations.

A three-cell unit (15.6 × 9 Å) contains two Mg2+·6H2O octahedra centered at the corners and face centers and four 4H2O squares centered about ±5.2 Å along a between the octahedra. The arrangement affords twenty hydrogen bonds near 2.75 Å, twelve between silicate and water layers and eight between water layers, and thirty-two hydrogen bonds near 3.0 Å within water layers. The remaining four hydrogens are not active in the bonding system. The environment of each water molecule is a distorted tetrahedron.

A broad infrared absorption band shows maxima at about 3600, 3450 and 3350 cm−1 at normal incidence, with increased activity in the highest and lowest energies when a flake is tilted. It is concluded that OH axes in the shortest bonds are more inclined to the cleavage planes than are the intermediate length axes.

Studies of the mineralogy of the northern part of the Atlantic Coastal Plain indicate that the heavy mineral content of the Cretaceous and Cenozoic sediments consists basically of two suites, a restricted mineral suite characterized by very stable minerals, and a full suite consisting of a great variety of igneous and metamorphic minerals. The restricted suite occurs in the nonmarine sediments and the full suite in the marine deposits.

The nonmarine Cretaceous deposits consist of kaolinite, with variable amounts of illite and its alteration products. Transition sediments like those of the Magothy formation contain kaolinite, illite, chloritic material and, occasionally, some montmorillonite. The marine sediments are characterized primarily by illite and montmorillonite. Thus, a limited heavy mineral suite and kaolinite are associated in nonmarine deposits, and a full suite and montmorillonite are found in marine sediments.

On the basis of available data the conclusion is reached that the different heavy mineral and clay mineral suites are a result of different source areas for the marine and non-marine sediments.

The suggestion is made that the formational concept cannot be employed with regard to the nonmarine sediments of the northern Coastal Plain but that, instead, a new concept be adopted based on depositional conditions within the framework of the control of the heavy and clay mineral assemblages.

The clay deposits of eastern Washington and northern Idaho are along the eastern edge of the Columbia River Plateau physiographic province. Three types of clay occur in the area: (a) residual clay derived from the Columbia River basalt of Tertiary age; (b) residual clay derived from the Cretaceous granodiorite and related intrusive rocks of the Idaho batholith; and (c) transported clay. The two types of residual clay were formed during a protracted lull in the outpouring of the Columbia River basalt, when the relief of land surface was low to moderate and the climate was warm and humid. The topography and climate during this interval were probably ideal for leaching and oxidation. The transported clay is chiefly a product of the weathered granodiorite and related intrusive rocks. Most of it accumulated in basins formed by damming of streams by basalt flows.

Kaolinite and halloysite are the principal clay minerals found in the area. The residual clay derived from basalt is chiefly composed of halloysite. Most of this clay is colored blue, gray or grayish black by finely disseminated ilmenite and locally it is stained blown by limonite; most of it has a relict basaltic texture.

The residual clay derived from granodiorite and related intrusive rocks contains both kaolinite and halloysite, and the transported clay is predominantly kaolinite. Both of these clays are white and contain abundant quartz grains and mica flakes. The residual clay has a relict granitic texture, and the transported clay has a well-developed bedding and is interbedded with elastic material.

Part of the research on the structure, synthesis, and properties of clay minerals in Yugoslavia is reviewed with particular reference to the following problems: (a) attempts to synthesize halloysite from solutions under normal conditions; (b) structure and properties of synthetic montmorillonites; (c) dehydroxylation of kaolin minerals under nonequilibrium conditions; (d) structural properties of metakaolin as shown by adsorption of colloidal gold; and (e) free silica in bentonites.