Seiichiro Uehara

Surface microtopography of lath-shaped hydrothermal illite by tapping-mode™ and contact-mode AFM

Lath-shaped hydrothermal illite particles in Izumiyama pottery stone were examined by contact-mode atomic force microscopy (CMAFM) and tapping-mode AFM (TMAFM) in air. With CMAFM, the lath-shaped particles showed interlacing patterns on the (001) surface in deflection images, while in height images such patterns were unclear. Also, evidence of artifacts caused by frictional forces between the surface and tip and/or edge effects were found in the CMAFM height images of the particle and Si substrate surfaces. In contrast, TMAFM showed interlacing patterns clearly in both amplitude and height images, and artifacts were barely evident. The TMAFM height images permitted the accurate measurement of 1.0- or 2.0-nm height steps corresponding to single or double mica layers, as well.Many lath-shaped particles in the Izumiyama hydrothermal illite exhibit interlacing patterns on their (001) surface, as shown by these AFM observations. The interlacing patterns are characterized by polygonal spirals with comparatively wide spacings and steps having a height of 1.0 or 2.0 nm. Generally a single lath-shaped particle has a single spiral center on the (001) surface, and 2 mica layers rotated 120° originate from the dislocation point. These support the view that lath-shaped illites belong to the 2M1 polytype. It is likely that these illite particles were formed by a uniform process of development that is characterized by very slow growth, spiral mechanisms in that growth and low supersaturation conditions.

ATOMIC FORCE MICROSCOPY STUDY OF HYDROTHERMAL ILLITE IN IZUMIYAMA POTTERY STONE FROM ARITA, SAGA PREFECTURE, JAPAN

The surface microtopographic observations and analyses of Izumiyama hydrothermal illite particles were made by utilizing tapping-mode atomic force microscopy (TMAFM). The Izumiyama illite particles showed platy to lath shapes. Platy particles exhibited various spiral growth patterns, i.e. circular, malformed circular, or polygonal single unit-cell layer spirals, polygonal parallel step spiral, or interlaced spiral patterns. The polygonal parallel step spiral and interlaced spiral patterns are formed by two single unit-cell layers rotated by 180° and 120° arising from a single screw dislocation point, respectively. The spiral patterns indicate that the illite particles have 1M, 2O and 2M1 polytypes. Lath-shaped particles show only interlacing patterns supporting the formation of 2M1 structures.Particles showing circular or malformed circular spirals were found to be thinner and to have narrower step separations than particles showing polygonal spirals. Polygonal platy and lath-shaped particles showing interlaced patterns tended to be thicker and to have wider step separations than the other polygonal platy particles.These results suggest that the Izumiyama illites crystallize as the result of a mechanism involving solution-mediated polytypes and spiral-type transformations of illite. The mechanism involves the Ostwald ripening process, i.e. a transformation of the polytype and spiral shape. The sequence of crystallization of the Izumiyama illite is: 1M circular spirals → 1M, 2O polygonal spirals → 2M1 polygonal spirals occurring during crystal growth and sequentially overgrowing on the initial particle surfaces. The super-saturation of the hydrothermal solution probably decreases gradually during the transformation, and this decrease may cause not only the transformation from a circular to a polygonal crystal morphology but also the development of a lath habit due to the inhibition of the growth rate in the [010] direction of the particle.

Chlorite in metabasites from the Mikabu and North Chichibu Belts, Southwest Japan

Chlorites formed as a replacement of phenocrysts in metabasites from the pumpellyite-actinolite to lower-greenschist facies Mikabu and North Chichibu belts in southwest Japan were studied by X-ray powder diffraction, electron microprobe analysis (EMPA) and high-resolution transmission electron microscopy (HRTEM). The metabasites contain a small quantity of fine-grained smectite and corrensite in the <1 pm size fraction. The chlorite also contains trace amounts of Ca, Na and K, which generally appear to be associated with smectite stacked in chlorite packets. The smectite layers comprise up to 13% of the chlorite domains. Theoretical estimates of the smectite ratio by the Wise method using EMPA data coincide well with the ratio determined based on HRTEM observations in most chlorites. However, in some chlorites with high proportions of Ca, Na and K, the cations cannot be reasonably attributed to smectite alone. Based on the present analyses, Ca, Na and K cations are also hosted in discrete interstitial phases of fine-grained smectite and corrensite as possible retrograde metamorphic products. These findings suggest that care should be taken in application of the Wise method to estimate the smectite ratio, and that the whole-rock chlorite composition may not be suitable as a geothermometer.

Development of an Iodine Immobilization Technique by Low Temperature Vitrification With BiPbO2I

This paper describes low temperature vitrification process with BiPbO2 I (BPI) as a promising immobilization technique in which Iodine-129 reacts with BiPbO2 NO3 (BPN) to form BPI, which is then solidified into a lead-boron-zinc glass matrix (PbO-B2 O3 -ZnO) using a low temperature vitrification process. Studies with EPMA, STEM-EDS and XRD found that iodine, lead and zinc were homogeneously dispersed in the waste form, and that there were no residual crystalline minerals in the amorphous glass matrix. Leaching tests conducted under typical geological disposal conditions show that iodine dissolves congruently with the BPI glass matrix in simulated seawater, whereas it dissolves incongruently in alkaline Ca(OH)2 solutions. This is due to retention within an altered surface layer.Copyright

Occurrence of Hydrothermal Alteration Minerals at the Jade Hydrothermal Field, in the Izena Hole, Mid-Okinawa Trough

Mineralogical and geochemical features of hydrothermal alteration minerals in the sediment cores from the Jade hydrothermal field in the Izena Hole, mid-Okinawa Trough, were studied by XRD, EPMA and TEM-EDS analyses. A core sample 1186MBL collected from the surface sediment near the sulfide chimney venting high temperature fluid up to 320 °C was characterized by occurrence of kaolinite, with sulfide minerals such as sphalerite and galena. The kaolinite would be related to be formed under acidic condition caused by oxidation and dissolution of the sulfide minerals by penetrating seawater. Core samples (1188MB, 1193MB) were collected from the surface sediment in the vicinity of clear hydrothermal fluid venting of ~100 °C, which is located in 400 m distant from the sulfide chimney. In these cores, occurrence of chlorite and smectite was identified. The chlorite in the core 1188MB had chemical composition close to Al-rich chlorite which is classified as sudoite, although chlorite found in other hydrothermal fields in the Okinawa Trough is characterized as significantly Mg-rich chlorite. Core samples of up to 4–6 m length were also collected near the low temperature fluid venting to study alteration in deep layers. One of two long core samples (BMS-J-2) was characterized by chlorite and illite assemblage below 380 cmbsf, while the other (LC-J-2) was characterized by abundant occurrence of K-feldspar below 300 cmbsf. Occurrence of euhedral crystals of K-feldspar in size up to several tens μm suggests the formation by precipitation from high temperature fluid.

AFM Study on Surface Microtopography, Morphology and Crystal Growth of Hydrothermal Illite in Izumiyama Pottery Stone from Arita, Saga Prefecture, Japan

Atomic force microscope (AFM) observation and analysis of Izumiyama hydrothermal illite (the weaker al- tered illite-kaolinite zone (IZ-1) and the higher altered illite zone (IZ-2)) were performed to understand the crystal growth mechanism and the relation between morphology and polytype of the illites. Our AFM results suggest that growth of the Izumiyama illite was controlled by a mechanism of solution-mediated polytype and spiral-type transformations, based on the Ostwald ripening process. The sequential variations could follow the changes in supersaturation and/or temperature of the solution. The paths of the thermal and supersaturation condition changes of the hydrothermal solutions for the two samples were estimated from the saturation state of the solution, which was evaluated by the step separation, polytype and mineral assemblage of the samples.

Characterization of Cement Alteration Process by Transmission Electron Microscopy with High Spatial Resolution

Application tests for advanced TEM analysis techniques were carried out to study the cement alteration processes associated with water penetration at high spatial resolution. Prior to TEM analysis, we measured the changes in the penetration coefficient and determined the characteristics of the penetrating water in order to gain a fuller understanding of the overall process. These experiments revealed that the process begins with the preferential dissolution of Ca(OH)2. After most of the Ca(OH)2 is dissolved out, the penetration coefficient increases, while the pH value of the water decreases. It has been demonstrated that scanning transmission electron microscope (STEM) techniques are quite useful for determining local structures and compositions in the cement at sub-micron meter spatial resolution. The preferential dissolution of Ca ions results in refinement of cement grains. When the Ca/Si ratio decreases to 1.05, most grains have a round shape in the sub-micron range. X-ray mapping suggests the formation of 3CaO·A12O3· xSiO2·(6-2x)H2O (x=0-3). Ettringite has been mostly dissolved out. But Mg ions remain still in form of brucite. When Ca/Si reaches 0.91, the morphology has changed to a mixture of fibers and granules. The fibers have been identified as a mixture of Calcium Silicate Hydrate Gel and silica gel. Quantitative EDX composition analyses have demonstrated that the granules are altered products of hydrogrossular, 3CaO·A12O3·2SiO2·2H2O, which have been predicted by previous theoretical studies. It is also been shown that hydrotalcite with Mg and Al has been also formed. The results thus obtained are in principle in accordance with the process predicted by previously proposed thermodynamic models.

Microtexture investigation of amblygonite-montebrasite series with lacroixite: Characteristics and formation process in pegmatites

Abstract Amblygonite–montebrasite series and lacroixite from Nagatare Li–Cs–Ta (LCT) pegmatite, Fukuoka Prefecture, Japan, were investigated by powder X-ray diffraction (XRD), electron microprobe analyses, and transmission electron microscope (TEM)/scanning transmission electron microscope (STEM) analyses. Scattered patchy or lamellar lacroixite was contained in montebrasite and amblygonite in all observed specimens. TEM/STEM observations revealed that the patchy and lamellar texture comprised lacroixite and low-fluorine montebrasite having same crystal orientations as that of host montebrasite and the boundaries corresponded to well-developed {110} planes. The observed microtexture was newly discovered, and it is an important evidence of the exsolution process. In XRD experiments conducted at high temperature, the unit-cell parameters of amblygonite were closer to that of monoclinic structures such as lacroixite with increasing temperature. Results suggested that scattered patches or lamellae of lacroixite were exsolution textures from a high-temperature phase. Montebrasite and amblygonite specimens from other localities involved varying textures corresponding to their occurrence. The amblygonite–montebrasite series from petalite-bearing pegmatite included low to high lacroixite contents and that from lower-temperature pegmatite with spodumene either did not possess or involved low lacroixite contents. Gem-quality montebrasite from drusy vugs formed at low temperature did not include any exsolution texture or lacroixite. The variety of texture of the amblygonite–montebrasite series indicated in this study generated new possibilities as the indicator of pegmatite-forming process.