Mafic chlorite from Benton, Arkansas was comminuted by rotary blending of a suspension, and the — 2 μm fraction separated by sedimentation in H2O. Droplets of suspension of the < 2 μm fraction were dried on a layer of Epoxy resin and then additional Epoxy was added and heat-cured at 48°C to form a resin sandwich. Cross-sections of 600–900 Å thickness were cut on a Reichert automated ultramicrotome. The sections were collected on standard electron microscope specimen screens, reinforced by vacuum evaporated C and examined by transmission electron microscopy (TEM). The Phillips EM 200 electron microscope was equipped with a “microgun” source to minimize heating of the specimen and to improve contrast and high resolution (HREM). Images of the (001) chlorite crystallographic planes spaced at 13·9Å intervals were visible on many of the particle sections. Imaging of the planes depended upon their being nearly parallel to the electron beam (within 0° 10’) and therefore, many particles which had other orientations did not show the 13·9Å image. Micrographs made before appreciable irradiation by the electron beam revealed images of fringes corresponding to the 7·22Å (002) spacing of chlorite. Loss of the 7·22 Å fringes and reinforcement of those at 13·9 A resulted from heating of the chlorite in the electron beam. This behavior is analogous to the well-known crystallographic effects of heating chlorite at 550–760°C.

The petrography of shale partings in carbonate rocks from eleven cores in the Illinois (Jeffersonville Formation) and Michigan Basins (Detroit River Formation) of Indiana indicates the presence of a K-bentonite which is interpreted as the Tioga Bentonite, an important stratigraphic marker in the middle Devonian rocks throughout the central and eastern United States. The clay mineral composition of the Tioga Bentonite of Indiana is interstratified illite and smectite, usually with admixed kaolinite. This composition stands in striking contrast to the simple illite suite without kaolinite in the normal terrigenous shale partings in the Devonian rocks of Indiana. Euhedral sanidine, high temperature albite, zircon, apatite, and the angularity of quartz grains found associated only with the interstratified clay mineral suite support the volcanic origin of these clay partings.

X-ray diffraction patterns for mixed-layer kaolinite-glycerine-saturated montmorillonite were calculated, taking into account the differences of scattering power of kaolinite and montmorillonite layers. The data were compared with the experimental results for two kaolinite-montmorillonite mixed-layer minerals. The probability parameters and the total number of layers in crystals were established.

The cation exchange process between tris(ethylenediamine)cobalt(III) and Na+ on mont-morillonite was studied by atomic absorption spectrophotometry, X-ray diffraction, differential thermal analysis, and nitrogen sorption at 78°K. The exchange of Co(en)33+ for Na+ was found to be extremely favorable, with a tendency toward segregation of the two kinds of cations in the mixed clays studied. Small amounts of Co(en)3+3 were found to lower the nitrogen sorption capacity of Na+ mont-morillonite while clays with high Co(en)3+3 content had greatly enhanced sorption. An explanation is offered in terms of a dual role of the Co(en)3+3 in determining the kind and amount of nitrogen sorption in the exchanged montmorillonite.

X-ray diffraction patterns of garnierites indicate that most samples resemble serpentine-group minerals or a talc-like mineral, or a mixture of these forms, and give respectively 7 Å and 10 Å basal reflections. From a survey of some 40 garnierites, four of predominantly serpentine type and seven of predominantly talc-like type were selected for detailed study. The talc-like garnierites exhibit little variation of the 10 Å basal spacing with low-temperature heating or with immersion in liquids, though some may contain a small proportion of expandable layers. Chemical analyses show considerable deviations of octahedral/tetrahedral cation ratios from the values 3/2 and 3/4 for normal serpentine and talc minerals, and may be interpreted in terms of mixed 1:1 and 2:1 layer types, either as separate phases and/or as interstratifications, or as defect structures of various kinds. The H2O + contents of the talc-like forms of garnierite are considerably greater than that of normal talc and point to a mineral of composition 3(Mg, Ni)O·4SiO2. 2H2O or [(Mg, Ni)3Si4O10(OH)2]H2O—a talc mono-hydrate formula. The green color of garnierites is related to the NiO weight per cent and a color index is derived based on the Munsell color charts.

Electron micrographs of 7 Å-type and 10 Å-type garnierites have been recorded at 5·104–105X magnifications to show the morphological character of these minerals, and at 106X magnification to show structural features of the particles. The 7 Å, serpentine-like minerals show a greater variety of morphological forms including tube- and rod-shaped particles and also platy forms and poorly defined, fluffy particles, probably aggregates. The 10 Å, talc-like minerals show mainly platy forms and fluffy aggregates, and generally very few tube or rod-shaped particles. At 106X magnifications, the 7 and 10 Å layer spacings are seen directly. In the samples examined, the 7 Å spacings are more clearly and more regularly defined than the 10 Å spacings.

Serpentine- and talc-like garnierites described in Parts I and II were heated at various temperatures up to about 1000°C and after each treatment were cooled and examined by X-ray powder diffraction. The serpentine-like garnierites at about 550°C, the temperature at which rapid dehydroxy-lation begins, formed a highly disordered phase. When the NiO content was low (approximately < 20 wt%), the disordered phase transformed directly to an olivine phase around 800°C, but when the NiO content was higher, various transitional phases were formed before an olivine phase appeared around 1000°C. A sepiolite-like phase was obtained with one sample around 800°C, and several samples showed face-centered cubic modifications between 900 and 1000°C.

The talc-like garnierites with low NiO content formed an enstatite phase around 800°C directly following the dehydroxylation reaction, but with high NiO contents an olivine phase became increasingly prominent between 850 and 1000°C. Identification of the mixed crystallizations possibly existing in the initial minerals is scarcely feasible on the basis of the products formed up to 1000°C.

A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v.-visible spectroscopy in the elucidation of structural, physical, and chemical properties of such systems. Spectra, which were obtained in the suspension, film, and single crystal states (where applicable), are interpreted in terms of iron-associated transitions. Microcrystalline clay minerals typically show Fe(lll) in octahedral oxo-ligand geometry whereas mica-type minerals may show a range of iron species, including octahedral Fe(III), tetrahedral Fe(III), and octahedral Fe(II). Iron affects the local site geometry and in “high iron” minerals may dictate layer geometry and subsequently the crystalline form.