Chapter 2 Weathering of volcanic ash and other pyroclastic materials

Nagasawa, Keinosuke

doi:10.1016/s0070-4571(08)70683-6

Cited by 22 publications

(14 citation statements)

References 36 publications

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“…For the rhyolitic tephra under the humid conditions in Japan, the allophane-halloysite transformation occurs after about 6,000 years (Wada, 1977;Nagasawa, 1978). However, this transformation in the samples occurs in very shallow horizons studied here (Fig.…”

Section: Clay Mineralsmentioning

confidence: 71%

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

2005

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Compositional and mineralogical (primary silicate minerals, volcanic glass, secondary minerals) properties of weathered basaltic ash soil ("Andisol") derived from Mt. Fuji, central Japan, with an age of ca. 6,000 y.B.P. to 240 y.B.P. were studied. X-ray fluorescence analysis indicates that the order of relative elemental mobilities during the weathering is Na, Ca > K > Mg > P > Si > Ti, Fe > Al > Mn.The trends of soil water chemistry (H 4 SiO 4 concentration) with depth were calculated based on a dissolution (volcanic glass)-precipitation (allophane) kinetics-fluid flow coupling model. In order to calculate the trends, the data on presentday annual rainfall, solubility of basalt glass, porosity and specific gravity of the soil, deposition rate of volcanic ash and grain size of volcanic glass were used. The calculated results were compared with analytical trends of soil water chemistry. From this comparison, the dissolution rate constant of basalt glass was estimated to be 10 -10.2±0.5 (mole Si m -2 s -1 ). This value is consistent with previously determined experimental long-term dissolution rate constant of basalt glass reported in the literature (Berger et al., 1994).

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Section: Clay Mineralsmentioning

confidence: 71%

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

2005

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“…Nagasawa (1978) showed that halloysite formed by alteration of volcanic glass is spherical, whereas that formed by the weathering of rock-forming minerals is tube-shaped. Thus, the dissolution rate of volcanic glass appears to have been faster than that of rock-forming minerals, and the solution around the volcanic glass easily became highly supersaturated.…”

Section: Clays and Clay Mineralsmentioning

confidence: 99%

Growth Conditions and Genesis of Spherical and Platy Kaolinite

Tomura

1985

Clays and clay miner.

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Abstract--Spherical and platy kaolinite crystals were prepared under several hydrothermal conditions. Spherical kaolinite was produced mainly at high solid/water ratio (1/4) and at low temperatures (150 ~ 200~ Platy kaolinite predominated in products from experiments with intermediate solid/water ratios (1/256-1/16) and at high temperatures. Boehmite predominated at low solid/water ratios (1/4096) at all experimental temperatures (180"-220"C). The results indicate that the growth of the spherical kaolinite was favored at high degrees of supersaturation, whereas the growth of the platy kaolinite was favored at relatively low degrees of supersaturation.

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“…These pyroclastics and volcanic rocks tend to be weathered chemically into various hydrous silicate such as ailophane, halloysite, smectite and kaolinite by interaction with water (Nagasawa 1978;Alien and Hajek 1989;Chamley 1989). The weathering processes can be divided simply into 2 fundamental reactions: 1) dissolution of starting materials by interaction with water and 2) precipitation of hydrous silicates in the water containing dissolved elements.…”

Section: Introductionmentioning

confidence: 99%

Analytical Electron Microscopic Study of the Noncrystalline Products Formed at Early Weathering Stages of Volcanic Glass

Kawano

Tomita

Shinohara³

1997

Clays and clay miner.

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Abstract--Formation processes of weathering products of pumice collected from a rhyolitic pyroclastic flow deposit were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). SEM clearly showed the presence of some weathering products adhering to the surface of pumice. XRD showed that the products were composed mainly of noncrystalline materials with a relatively small amount of halloysite (I0 ~k). TEM and EDX revealed texture transformation sequences from the earliest weathering product to a final product of halloysite as follows: 1) precipitation of very thin flaky or film-like noncrystalline Al-hydroxide; 2) transformation into irregularly aggregated A1-Fe-Si-rich fibrous material; 3) morphological changes to rounded aggregates; 4) development of halloysite-tike curled domains with successive decrease in Fe content; and 5) further development of curled domains in rounded aggregates. These materials must be metastable phases at early reaction stages with kinetics limiting formation of the stable equilibrium phase of kaolinite.

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Chapter 2 Weathering of volcanic ash and other pyroclastic materials

Cited by 22 publications

References 36 publications

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

Growth Conditions and Genesis of Spherical and Platy Kaolinite

Analytical Electron Microscopic Study of the Noncrystalline Products Formed at Early Weathering Stages of Volcanic Glass

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