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.

Shales of marine, brackish-water, and nonmarine origin, collected from cyclothems of Pennsylvanian age, were analyzed chemically and mineralogically. Clay mineral identifications were accomplished using x-ray diffraction and differential thermal analysis techniques. Summations of the structure amplitudes of the individual clay minerals formed a basis for semi-quantitative ratios between illite and kaolinite-chlorite. Illite was found to be enriched in the marine shales. The origin of the authigenic clay minerals in the shales is discussed from two aspects. The first and probably the more correct uses the thesis that the ultimate clay mineral is built up from a skeletal aluminum-silicate structure; the second discusses the origin of the clay minerals from a purely colloidal point of view. Trace element determinations, pH values, and pipette analyses are also included as a part of this study.

The rivers of the Chesapeake Bay area carry in suspension predominantly a well formed to degraded illite with minor amounts of kaolin and accessory degraded chlorite. Montmorillonite is rare.

Electron microscope photographs of suspended and bottom sediment clays in the James estuary indicate a decrease in floccular size and an increase in crystal size with increasing salinity.

A chlorite-like clay is forming in the Chesapeake Bay estuaries. Its thermal stability increases with increase in the salinity of the environment and with depth in the sediments. This material seems to arise from the diagenesis of degraded illite in the Chesapeake Bay area, but it has also been observed to result from diagenesis of a montmorillonoid in the Atchafalaya region of the Gulf Coast.

The geochemical relations of chloride, sodium, calcium, potassium, and magnesium in the clays of the James estuary support the hypothesis that chlorite is forming in the estuarine and marine environment.

Clay mineral studies of recent sediments from a diversity of environments in the vicinity of Rockport, Texas, have been made as part of American Petroleum Institute Project 51.

The bulk of the argillaceous material in these sediments is a complex mixture of poorly crystallized three-layer clay minerals. Problems of the identification and nomenclature of the components of such mixtures are considered.

Variations in areal distribution of the clay mineral constituents indicate progressive diagenesis in response to changing chemical environment. The gradual loss of montmorillonitic source material with the ultimate formation of poorly crystalline illitic and chloritic phases has been related to variations in environment. Environmental criteria based on clay mineral compositions are suggested.

Clay samples were taken from formations outcropping between Corpus Christi and Uvalde, Texas, during the annual field trip of the Corpus Christi Geological Society in 1953. The geologic age of the formations sampled ranges from Quaternary to Upper Cretaceous. Both surface and near-surface samples were taken. The results of examination of these samples by use of x-ray diffraction and electron microscope techniques indicate marked differences in the relative proportions of montmorillonite, kaolinite, and illite. Comparison of surface and near-surface samples indicates the probable course of weathering.

The behavior of anorthite under the test conditions is similar to that of other feldspars and quartz. The solubility of anorthite in pure water was measured at 300 bars pressure between 200° and 350°C. Under these conditions, anorthite not only partially dissolves, but also disintegrates by shedding small particles of crystalline material which forms, with matter in true solution, a nonhomogeneous suspension. Two zeolites (afwillite and xonotlite) develop at the higher temperatures. Their stability is determined by the CaO:SiO2 ratio of the solution.

The anorthite fragments react with the solution. They maintain their identity although their composition and structure gradually change over a wide temperature range. Possibly the zeolites inherit their structure from the altered anorthite. It is almost certain that xonotlite inherits its structure from afwillite.

Electrodialyzed suspensions of clay minerals are viewed generally as insoluble silicates in which the exchange complex is saturated with hydrogen. An investigation of the relative activities of different exchangeable ions on beidellite clay brought to light the fact that a freshly prepared hydrogen clay containing a trace of the non-adsorbed chloride ion, when filtered, yielded a solution containing the chloride ion in association with silica rather than with hydrogen.

The filtrate from the freshly prepared suspension was clear and had a pH value of 5.5. After standing 24 hours the filtrate became cloudy and the pH value dropped to 3.5 corresponding to the concentration of acid produced by the chlorides in association with hydrogen. Analysis of the clear filtrate revealed that the chlorides were associated with silica. The amount of soluble silica in the filtrate from the clay suspension was related directly to the amount of exchangeable hydrogen in the clay. No soluble silica was present in the filtrate from clay which had been neutralized with either potassium or calcium hydroxide.

The recent interest in the determination of the phase diagrams for many systems involving water as one component has been in those systems which are of greatest importance to clay mineralogy.

The importance of both published and more recent work on synthesis of the clay is demonstrated in the ability to prepare chemically pure, mineralogically homogeneous kaolinites, montmorillonites, micas, and chlorites. The stability and identification of the clay minerals are discussed in relation to some of the major problems of clay mineralogy. Some of the chief objections to data obtained by the usual hydrothermal techniques are treated at length.

The colloidal properties and base-exchange characteristics of five deposits in four different areas were determined. The variations of the clay were, in general, a function of the amount of overburden and have been related to that dimension.

From the standpoint of appearance, two types of clay were found in these areas. The highest grade clay has a yellow color whereas the other type, a blue clay, is customarily found to be of lower grade.

Differential thermal studies of the yellow and blue clay, when correlated with variations in colloidal properties, strongly suggest that the change from blue to yellow is due to oxidation of iron.

The primary cause for variation in properties is due to the Na/Ca ratio in the exchange positions regardless of whether the iron in the clay is in the ferrous or ferric state. Examination of purified clays indicates that the exchangeable base ratio of the field bentonites lies in a zone of instability. This zone occurs when the divalent ions amount to 40 to 60 percent of the base-exchange capacity.

Chromium-bearing members of the montmorillonite group have been reported heretofore only for Russian localities, where they have been related genetically to serpentines. A green mineral which occurs in high-angle fissures in the Morrison formation (Upper Jurassic) near Thompsons, Utah, contains about 2 percent Cr2O3. Data were obtained by optical and electron microscopy, x-ray powder diffraction, and gravimetric and spectroscopic chemical methods. The ultimate source of the chromium remains an unresolved geochemical question, as do the sources of vanadium and uranium in the Morrison sandstone.

Nodules of alunite and hydrated halloysite occur in the upper part of the Cretaceous Blue Hill shale at three localities in west-central Kansas. They have formed at the contact of septarian concretions with the shale and are associated with gypsum. The nodules are judged to have been formed by the action of sulfuric acid from pyrite on the potassium-bearing minerals of the Blue Hill shale, perhaps under special conditions of pH and Eh produced locally by the presence of septaria.

The minerals were studied and identified by x-ray diffraction, thermal data, chemical analysis, and electron and light microscopy.

The clay minerals in a soil developed from Lenoir limestone (Ordovician) in Augusta County, Va., are kaolinite and chlorite. The Lenoir limestone contains clay partings consisting of hydrous mica, and the clay in the soil is considered to be residual from that in the parent limestone and modified by soil-forming processes (podzolic). X-ray diffraction patterns of the clay fraction (<2μ) from samples from different positions in the profile show a reduction in hydrous mica and an increase in kaolinite and chlorite content as the A horizon is reached. Partial chemical analyses of the whole soil and of the clay fractions are given, as well as pH and ion-exchange capacity determinations. The silica-alumina ratios are similar to those characteristic of podzolic soils, and excess silica in the A horizon accumulates as recrystallized quartz together with chert which is considered to be residual from the limestone. Mechanical analyses by the standard pipette method show that the quantity of clay in the soil varies from 17 percent at the surface to 61 percent at 26 inches (C horizon).

A comparative study of two soil profiles derived from a biotite-granite and from a metagabbro in the Piedmont Province of North Carolina was made. Intensive weathering of the granite has yielded a soil (Durham) with a clay fraction composed of a kaolinite-halloysite intermediate, mica, and quartz. Restricted weathering of the metagabbro has resulted in a soil (Iredell) with a clay fraction composed of a complex assemblage of chlorite, beidellite, vermiculite, interlayered talc-like minerals, and quartz.

The data indicate that the Durham soil is derived from the severe alteration of a granite and that it represents an advanced stage in soil formation. The Iredell soil has been derived from the less active weathering of a metagabbro and represents a retarded, youthful stage in soil formation. The clay mineral assemblage of the Durham is that of a comparatively stable end product of weathering; that of the Iredell is indicative of a complex, unstable early stage in weathering.

This paper presents data on clay-size material in the loess of southwestern Iowa. Most of the loess samples studied are Wisconsin in age. Regional distribution of clay-size material in the loess is discussed, and data are given on the modes of occurrence of clay in the loess. The following test methods were used to study the clay fractions of selected loess samples: Mechanical analysis, differential thermal analysis, cation-exchange determinations, refractive index determinations, and x-ray diffraction techniques. These tests indicate a uniformity in clay-mineral composition, with montmorillonite and illite group minerals predominating. Clay contents from mechanical analysis are correlated with various properties of the loess; in most cases the properties appear to be linear functions of the clay content. The plastic limit is discussed in detail.

A new technique for the x-ray analysis of soil colloids is proposed based on the finding that the interlayer swelling of montmorillonite persists in the presence of salt solutions and that the x-ray reflection representing the d(001) spacings becomes intensified in salted gels. The technique consists in flocculating the colloid from a suspension with sodium chloride, removing the “free” Fe2O3, Al2O3, and SiO2 by means of a solution of sodium citrate and sodium hydrosulfite, separating the cleaned colloid from the solution as a salted paste, and as such subjecting it to x-ray analysis. The method is not only more rapid than other recommended methods for x-ray analysis of soil colloids, but also — and which is of the utmost importance — yields a much more accurate picture of the mineralogical composition, particularly with respect to the content of the mica and the montmorillonite-type clays.

Analyses were made of 12 clay fractions and one silt fraction taken from 10 different soil horizons and clay deposits. The analyses presented were selected to represent a wide variety of analytical problems with materials containing 2:1 layer silicates, 2:2 (chlorite) layer silicates, varying amounts of 1:1 layer silicates, and in some cases with appreciable amounts of quartz, feldspars, gibbsite, hematite, magnetite, and (or) anatase.

The analyses were performed by x-ray diffraction, specific surface, integral heating weight loss, and elemental analyses. The x-ray diffraction analyses included both wedge-powder (film recorded) and oriented (Geiger counter recorded) techniques. Vermiculites of soils were found to vary in the degree to which K-saturation would close the interlayer space, but vermiculite is established by: (a) a 14 A spacing when solvated (even with glycerol); (b) closure of the interlayer spacing on heating to 500° C; and (c) an interlayer surface of about 800 m2 per gm. In the absence of adequate criteria, vermiculites can be mistakenly identified as chlorites.

The data obtained from the various techniques were combined by a system of allocation so that the minerals reported represented a unique fit of all the data. The specific surface measurement, including the measurement of interlayer surface, is a key criterion in the allocation. Interstratified (“mixed layer”) layer silicates are determined as the individual component minerals.

The beidellite of Iron River and Putnam soil clay finer than 0.08 microns is extensively interstratified with chlorite, mica, and vermiculite. No discrete x-ray crystalline zones of any of the latter three minerals were observed, but a 19.6 to 19.2 A spacing may be indicative of a superlattice of these materials and beidellite with mica and chlorite at the electron density nodes. A titaniferous ceramic clay contains 43 percent mica (as determined by allocating the 5.03 percent K2O to muscovite), 20 percent kaolinite (water loss in 300–525°C range), 21 percent TiO2 and 17 percent of other constituents (by elemental and surface analysis). This occurrence of the full complement of K2O in clay micas (both biotite and muscovite type) is general for the various clays examined, when the interlayer surface is calculated to halloysite, vermiculite, and montmorin. A general occurrence of inter-stratification of layer silicates is proposed.

Fifteen pure montmorillonites selected on the basis of minor differences in x-ray diffraction and differential thermal analysis data were treated with ethylene glycol, piperidine, and dodecylamine. X-ray and differential thermal data of the resulting complexes lead to the following conclusions:

(1) The complexes of montmorillonites with a given organic compound show differences ascribable to differences in the character of the montmorillonites. Attempts to relate variations in organic complexes to exchangeable cations, chemical composition, and collodial properties of the montmorillonites met with very limited success.

(2) All montmorillonites are mixed-layer sequences; i.e. adjacent layers differ from one another in composition, structure, or some other factor. It is suggested that mixed layering of this nature may also occur in other three-layer clay minerals.