Green mica which had been found in the Jangsan Quartzite (metamorphosed orthoquartzite) of Cambrian age, exposed in the Janggun mine area, Republic of Korea, was mineralogically investigated. As a result, it has been confirmed that the mineral is vanadium-bearing muscovite containing a small amount of chromium. The mineral flakes occur mainly along the boundaries between quartz grains, closely associated with vanadium tourmaline and graphite. The mineralogical properties of the dark green variety may be summarized as follows.
Basal cleavage is very perfect, optically negative, 2V=35°36'(observed), 31°10'(calculated). Refractive indices:α_D=1.573, β_D=1.610, γ_D=1.613, γ_D-α_D=0. 040 (all±0.001). Density (calculated) =2. 84g/cm³. Analysis by electron microprobe gave: SiO₂ 44.70, TiO₂ 0.53, Al₂O₃ 31.03, Cr₂O₃ 0.80, V₂O₃ 5.09, FeO 0.89, MgO 0.56, Na₂O 0.34, K₂O 10.51, sum 94.45 (all in weight percent). This corresponds to the formula on the basis of 0=22:(Na_0.09 K_1.83) _Σ1.92 (Al_3.10 Ti_0.06 Cr³⁺_0.09 V³⁺_0.56 Fe²⁺_0.09 Mg_0.11) _Σ4.01 (Si_6.11 Al_1.89) _Σ8.00 O₂₂. X-ray study showed the mineral to be two-layer monoclinic, 2M₁ polytype, space group C2/c or Cc with a=5.210, b=9.032, c=20.086 Å, β=95°38'. The strongest reflections (30 given) are, 10.01 (66)(002), 5.00 (24)(004), 4.48 (12)(110), 3.50 (11)(114), 3.34 (100)(006), 3.21 (12)(114), 2.996 (15)(025), 2.866 (13)(115), 2.797 (10)(116), 2.571 (16)(202), 1.997 Å(31)(00.10). TG curve shows the gradual and continuous weight decrease from 100 to 1000°C. DTA curve shows extremely broad endotherm with a maximum at 600-700°C. The infrared absorption spectrum is almost identical with that of normal muscovite. The strong absorptions are; 3630cm^-1 in OH stretching region, 471, 530, 750cm^-1 and a triple at 1080, 1035, 990cm^-1 in lattice vibration region. The material is shown in electron micrographs to occur in small, poorly-defined flakes commonly grouped together in irregular aggregates. Selected-area electron diffraction pattern from a thin, single particle shows the hk diffraction spots with a pseudo-hexagonal array.
From the geological environments of the Janggun mine area and the mode of occurrence of the present green mica, it may be concluded that vanadium and chromium present in the mineral are primary constituents, and that the mineral is of metamorphic origin rather than hydrothermal or metasomatic.

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DTA and TG curves for unground and ground materials prepared from six Mg-chlorite specimens with different crystal sizes have been described. The results indicate that the variations of thermal patterns of Mgchlorites, which are particularly considerable in the endotherm or weight loss due to interlayer dehydroxylation, are primarily caused by the different size of crystals composing the material under experimentation.

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A nickeliferous sepiolite sample from New Caledonia has been studied by means of thermal analysis, electron micrography, electron diffraction analysis, X-ray diffraction analysis, infrared analysis, chemical analysis and acid dissolution experiment. Quantitative X-ray diffraction analysis shows that this sample is a mixture of 80% sepiolite and 20% nickeliferous talc. The electron micrographs show that this sample is composed of fibrous particles. The heated specimens at 800°C and 900°C show the absorption bands at 3665 cm^-1, 3655 cm^-1, 3645 cm^-1 and 3625 cm^-1 in the OH region. The wave numbers of these bands are in good agreement with the data of synthetic and natural nickel-rich talc (willemseite). The intensity ratios of these peaks indicate that Ni ions are present in octahedral sites of nickeliferous talc. The value of Ni concentration ranges between 0.788 and 0.872. Using these values for nickeliferous talc and results of wet-bulk chemical analysis, the structural formula of nickeliferous sepiolite in this sample ranges between
(Si_11.98Al_0.02)(Fe_0.01Mg_5.67Ni_2.15) 0_32.00 5.76 H₂O and
(Si_11.98Al_0.02)(Fe_0.01 Mg_5.82 Ni_2.21) 0_32.00 5.93 H₂O.
The intensities of X-ray diffraction peaks calculated using the formula of Mg₆ Ni₂-sepiolite are in good agreement with those observed.

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Curves of shear stress against shear rate for aqueous imogolite suspensions have been determined using a rotary viscometer. At concentrations of 0.1%(w/v) and above, these suspensions have a pronounced gel character and the curves obtained during acceleration and deceleration of the rotor do not coincide but form a (hysteresis) loop. With successive cycles of shearing, the area enclosed by such loops is progressively decreased, indicating that imogolite gels behave like a pseudoplastic material in that strong shearing action produces an irreversible breakdown of the gel structure. This is confirmed by scanning electron microscopy (SEM) of the quick-frozen gels, showing that shearing has distorted and ruptured the fibre bundles of imogolite. Raising the suspension pH from 7 to 9 gives rise to a phase consisting of a condensed, semi-rigid gel in which the fibre bundles have partially aggregated to form a sheet-like structure. Air-drying the suspension, followed by prolonged mechanical stirring in water, produce a system with no gel character. SEM shows that the air-dried material has a sheet structure from which fibre bundles are totally absent.

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Mt. Chokai is located near the border of Akita and Yamagata Prefectures, Japan, and is an andesitic volcano belonging to the Chokai Volcanic Zone. It had often been erupted and the phreatic eruption took place in March to April, 1974, and ejected volcanic ash containing pyrite. Recently, the water of Shirayuki River flowing out from the northern foot of Mt. Chokai have been changing from neutral to weakly acid, and that of the Iwamata River having a number of low-temperature springs at its upper course became weakly acid with the pH value of about 4.5 in 1976 (Akita Prefecture, 1978). Stream-deposits are found on a marsh and on a stream bed at the upper course of the Iwamata River (Fig. 1). The mechanism of occurrence of allophane in stream-deposits is studied in the present work.

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