Textural Variation and Composition of Bentonite Derived from Basaltic Ash

Konta, J.

doi:10.1346/ccmn.1986.0340305

Cited by 22 publications

(13 citation statements)

References 3 publications

(2 reference statements)

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“…Smectite crystals are present in the form of wavy flakes, forming characteristic honeycomb textures, which might be due to dehydration of the specimens in vacuum ( Figure 6). No systematic relationship between the smectite morphology and the location of the flakes was observed, contrary to the findings of Konta (1985). The smectite flakes have been formed via two ways: a) at the expense of volcanic glass, which in places, has led to pseudomorphic replacement textures ( Figure 6), (Khoury and Eberl 1979), and b) replacement of igneous feldspars, mainly plagioclases ( Figure 6), which also has led to pseudomorphic textures ( Figure 7).…”

Section: Morphology and Mineral Chemistrymentioning

confidence: 73%

Origin of the Bentonite Deposits of Eastern Milos, Aegean, Greece: Geological, Mineralogical and Geochemical Evidence

Christidis

Scott

Marcopoulos

1995

Clays and clay miner.

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Abstract--The Lower Pleistocene bentonite deposits of Eastern Milos, Greece have been formed at the expense of volcaniclastic rocks under submarine conditions. Systematic variation of the major chemical elements reveals that the deposits were formed from different precursors which were erupted from different volcanic centers belonging to at least two separate volcanic provinces. The volcanic eruptions were probably subaqueous. The major authigenic phases are smectite, K-feldspar, opal-CT and the zeolites mordenite and clinoptilolite. The deposits have a complex history and have been affected by hydrothermal alteration.The geological features ofbentonites coupled by the presence of abundant authigenic K-feldspar indicate that alteration of the parent volcanoclastic rocks took place under low temperatures and is probably not related to hydrothermal alteration, which is a separate event. Hydrothermal alteration has modified both the mineralogical characteristics and the properties of bentonites. Alteration of the parent rocks to bentonites was favoured by high water : wall rock ratios and fluid flow and is associated with leaching and subsequent removal of Na, K and Ca. The source of Mg was the parent rocks and only small scale Mguptake from the sea water has probably taken place. The formation of authigenic K-feldspar has probably been favoured by a high K § + activity ratio and high Si activity of the pore fluid. Such conditions might have been favoured by the pH conditions and the cooling history of the parent rocks.

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Section: Morphology and Mineral Chemistrymentioning

confidence: 73%

Origin of the Bentonite Deposits of Eastern Milos, Aegean, Greece: Geological, Mineralogical and Geochemical Evidence

Christidis

Scott

Marcopoulos

1995

Clays and clay miner.

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“…%. The low K20 content in the bentonites attests to the low mobility of K. The high mobility of Ca and Mg in the aqueous environment contributes to a rapid attainment of chemical homogeneity between the hyaloclasts and free pores (Konta, 1986). The Ca/Na ratio of montmorillonite systematically decreases from the inner part of the alteration zone (Type-M1 montmorillonite) to the outer zone (Type-M2).…”

Section: Clays and Clay Mineralsmentioning

confidence: 99%

Clay Minerals in Hydrothermally Altered Volcanic Rocks, Eastern Pontides, Turkey

Çelik

1999

Clays and clay miner.

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Abstract--Extensive hydrothermal alteration is observed around volcanogenic massive sulfide deposits. These deposits are related to Late Cretaceous volcanism in various parts of the Eastern Pontide province. Mineral assemblages resulting from alteration consist of mostly clay minerals and silica polymorphs, some sulfate minerals, and scarce zeolite minerals. The clay minerals are kaolinite, illite, and smectite. These minerals were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive spectrometry (EDS), X-ray fluorescence spectroscopy (XRF), and differential thermal analysis (DTA)-thermal gravimetry (TG) techniques. The illite and the toseki deposits are a result of hydrothermal alteration of dacitic-andesitic volcanites. Two groups of bentonite deposits occur; the first mainly formed by hydrothermai solution whereas the second group resulted from halmyrolysis.The smectite in these alteration zones is generally montmorillonitic in composition and the interlayer cation is mostly Ca and lesser amounts of Na. The SiO 2 and F%O 3 contents of the hydrothermal bentonites are higher than those of the halmyrolysis smectites; however, the MgO content of both groups is similar. The Na20 and K~O contents of both groups are generally <0.5%. The hydrothermal bentonites are not plastic and have open honeycomb microtextures, although the halmyrolitic smectites axe plastic with ultrafine and rod-shaped textures. Illite, which contains some smectite layers, is a 1M polymorph, and has an asymmetry to the low-angle side of the XRD peaks. The impure illite deposits contain various combinations of smeetite, kaolinite and gypsum, galena, sphalerite, pyrite, goetite, and quartz. The illite has >35 wt. % A1203. The toseki raw material, which may be possibly useful as a porcelain raw material, is composed mainly of illite, kaolinite and quartz, or illite and quartz. The crystallinity of the kaolinite is poor.

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“…Minute fragments of sodium-rich plagioclase, potassium feldspar, quartz, and muscovite are ubiquitous accessories of the original hyaloclasts. Together with kaolinite, they formed from the underlying fresh or kaolinized orthogneiss (Konta 1986;Hradil et al 2004).…”

Section: Methodsmentioning

confidence: 99%

Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experiment

Stricek¹,

Šucha²,

Uhlík³

et al. 2009

Geologica Carpathica

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Abstract:Bentonite is a basic component of most concepts of multibarrier systems in underground radioactive waste repositories. It is important to determine the bentonite stability under the conditions close to the future real situation. The paper brings the detailed mineral and structural analyses of smectites from the bentonitic material exposed to the long term Mock-Up-CZ experiment. The compacted barrier blocks and residual filling contained 85 % of bentonite from the Rokle deposit, 10 % of quartz sand and 5 % of graphite. They were exposed to temperatures of up to 90 °C for almost 4 years. Quantitative mineral analyses, crystal size distributions, FTIR spectra, as well as cation exchange capacity and layer charge density show high mineral stability of the Rokle bentonite under the conditions of Mock-Up-CZ experiment. Small changes in the crystal sizes and slight change in the layer charge as a consequence of the experimental alteration could be linked to the hydration and the variation of the geochemical environment of the experiment.

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Textural Variation and Composition of Bentonite Derived from Basaltic Ash

Cited by 22 publications

References 3 publications

Origin of the Bentonite Deposits of Eastern Milos, Aegean, Greece: Geological, Mineralogical and Geochemical Evidence

Origin of the Bentonite Deposits of Eastern Milos, Aegean, Greece: Geological, Mineralogical and Geochemical Evidence

Clay Minerals in Hydrothermally Altered Volcanic Rocks, Eastern Pontides, Turkey

Mineral stability of Fe-rich bentonite in the Mock-Up-CZ experiment

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