The origin and control of colour of white bentonites from the Aegean islands of Milos and Kimolos, Greece

Christidis, George E.; Scott, Peter W.

doi:10.1007/s001260050092

Cited by 42 publications

(25 citation statements)

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“…Bentonite samples were collected from an alteration profile described by Christidis and Scott (1997) and Christidis (1998a), of the Prassa Ignimbrite, consisting of six different alteration zones (Figure 1). The mineralogy was determined by X-ray diffraction (XRD) using a Philips diffractometer equipped with a PW1710 control unit, operating at 40 kV and 30 mA, using Ni-filtered CuKet radiation.…”

Section: Methodsmentioning

confidence: 99%

“…Chemical analyses of the rocks in the Prassa alteration profile and calculated water : rock (WR) ratios (after Christidis, 1998a Sample SM285 corresponds to the fresh glass, SM283 to the glass + smectite zone, SM282 to the smectite + opal-CT zone, SM280 and SM278 to the smectite zone, and SM277 and SM261 to the smectite + mordenite zone. Characterization of the alteration zones is from Christidis and Scott (1997).…”

Section: Formation and Crystal Growth Of Srnectitementioning

confidence: 99%

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Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Christidis

2001

Clays and clay miner.

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Abstract--The low-temperature alteration of a rhyolitic rock from Kimolos Island, Aegean, Greece, yielded an alteration profile characterized by gradual transition from fresh glass to bentonite containing homogeneous Chambers-type montmorillonite and then to a mordenite-bearing bentonite. Both mordenite and smectite were formed from poorly crystalline precursors, which probably had compositions comparable to that of the crystalline end-product. However, their composition may have been modified to some degree after reaction with the fluid phase. Particle length and width measurements of smectite crystals yielded lognormal profiles, which suggest supply-controlled crystal growth in an open system or random ripening in a closed system. The former mechanism is in accordance with the observed sustained supply of Mg and Fe by the fluid phase throughout the alteration profile and is believed to be the dominant formation mechanism of smectites in bentonites in general. In the mordenite-bearing zone, random ripening is expected in domains with low permeability, in which the system was essentially closed, favoring the formation of mordenite. The level of supersaturation with respect to smectite was probably lower in the mordenite-bearing zone. Smectite probably affected pore-fluid chemistry either through ion exchange or via dissolution of initially formed K-bearing smectite. The latter process raised the K+/(Na + + Ca 2+) activity ratio of the pore-fluid favoring K-bearing mordenite.

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Section: Methodsmentioning

confidence: 99%

Section: Formation and Crystal Growth Of Srnectitementioning

confidence: 99%

Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Christidis

2001

Clays and clay miner.

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“…When leaching is not effective, zeolites crystallize usually from precursor gels (Mariner and Surdam 1970;Surdam 1977;Taylor and Surdam 1981;Steefel and van Cappellen 1990), while smectite generally forms in the initial stages of the alteration Gude 1968, 1973;Dibble and Tiller 1981;Hay and Guldman 1987). Leaching of Si from acidic rocks might lead to bentonites without silica polymorphs (Zielinski 1982;Christidis and Scott 1997). When excess Si remains in the system, opal-CT forms (Henderson et al 1971;Christidis and Dunham, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…However, this does not seem to be always the case. Recently Christidis and Scott (1997) described the formation of Chambers-type montmorillonite by alteration of an ignimbrite. This indicates that, in open systems, the introduction of key chemical elements might influence the composition of the neoformed smectites and, consequently, the alteration of the parent rock.…”

Section: Introductionmentioning

confidence: 99%

Comparative Study of the Mobility of Major and Trace Elements During Alteration of an Andesite and a Rhyolite to Bentonite, in the Islands of Milos and Kimolos, Aegean, Greece

Christidis

1998

Clays and clay miner.

143

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Abstract--Progressive alteration by seawater of an andesite in the Aegean Island of Milos and an ignimbrite in the Aegean Island of Kimolos, Greece, formed bentonites with or without zeolites. Both profiles are dominated by migration of alkalis and uptake of Mg, Fe and H20, while A1 and Ti are immobile. The relative removal of alkalis controls the formation of either smectite or zeolites. The behavior of Ca and Si depends on the chemistry of the parent rock. In the rhyolitic profile, alteration is controlled by gain of Mg, Fe 2 § and Ca and loss of Na, K and Si, while in the andesitic profile by gain of Mg and Fe 2 § and loss of Na, K and Ca. In both profiles, significant uptake of SO4 = was not observed. Moreover Zr, Nb, V and Ni are immobile and have been enriched residually, while Sr, Rb and Y are lost in both profiles. Thorium is immobile in the rhyolitic profile but is leached in the andesitic profile. Also, the rare earth elements (REE) display fractionation in both profiles; the degree of fractionation increases with the degree of alteration to bentonite. Fractionation of the REE in both profiles and mobility of Th in the andesitic profile are related to the existence of monazite (rhyolitic profile) and apatite (andesite profile). The REE and Th appear to partition into phosphates rather than smectite.The mobility of Y coupled with the immobility of Nb increases the Nb : Y ratio with advancing alteration, rendering discrimination diagrams that use this ratio to determine the nature of the prototiths misleading. Mass balance calculations showed that in the smectite-rich zones the water:rock (WR) ratio might be as high as 13:1 in both profiles, while in the zeolite-bearing zones it is about 5.5:1. Such WR ratios explain the observed extensive mass transfer and suggest that the pore fluid chemistry might overprint the chemical characteristics of the parent rocks controlling smectite and bentonite chemistry.

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“…Por último el ópalo C es escaso y su interés principal estriba en su valor científico en geología por ser marcador durante la diagé-nesis (9). Las fases mencionadas además de ser los constituyentes mayoritarios de las rocas siliceas pueden aparecer como minerales minoritarios en depósitos de interés económico tales como bentonitas, o caolines, siendo normalmente perjudiciales para sus aplicaciones industriales, por lo que es necesario su identificación y el desarrollo de técnicas de separación (10).…”

Section: Introduccionunclassified

Caracterización y respuesta al tratamiento térmico de rocas silíceas opalinas

Bustillo¹,

Garcı́a²,

Pérez³

2000

Bol. Soc. Esp. Ceram. Vidr.

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En las rocas opalinas se encuentran diferentes fases de la sílice que son poco conocidas y que ante los tratamientos térmicos responden de forma diferente. Rocas opalinas de diferentes ámbitos sedimentarios e hidrotermales se estudian mediante difracción de rayos X (DRX) y espectrometría de infrarrojos, analizando la respuesta del polvo natural y después de un tratamiento térmico a 1.050ºC durante 24 horas. El objetivo es la diferenciación de las distintas estructuras de la sílice que pueden aparecer en las rocas opalinas, las variaciones que presentan dichas estructuras, y su cambio ante los tratamientos térmicos. En la mayoría de las muestras, la fase silícea encontrada es la denominada ópalo CT. El ópalo CT es un interestratificado de cristobalita y tridimita de estructura compleja que responde, en los análisis de DRX ,con perfiles distintos, principalmente en el intervalo de 19º a 25º 2θ. Se definen tres tipos básicos en este intervalo que se denominan "perfiles ensanchados (E), de hombro (H) y de dos picos (2P)". Estos tipos tienen relación con la proporción de tridimita en el interestratificado (va aumentando desde los perfiles ensanchados a los de dos picos), el tamaño de cristal del ópalo (los ensanchados y los de hombro tienen menor tamaño), y la reactividad ante los calentamientos a 1.050ºC (va siendo progresivamente menor desde los perfiles ensanchados a los de dos picos). Las muestras menos reactivas resultaron ser las que poseían mayor proporción de tridimita en el interestratificado. En espectrometría de infrarrojos, los ópalos CT no manifiestan diferencias importantes entre sí, pero las muestras con perfiles ensanchados y de hombro presentan organizaciones algo distintas y mayor proporción de agua. No se han encontrado variaciones entre las estructuras de los ópalos formados en ambiente hidrotermal y los formados a temperatura ambiental, aunque en algunas muestras hidrotermales aparece ópalo C o una cristobalita α independiente junto al ópalo CT. Durante los tratamientos térmicos tampoco aparecieron diferencias. Palabras clave: ópalo CT, tratamientos térmicos, DRX, espectrometria infrarrojos Characterization of opaline rocks and their behaviour UNDER HIGH temperaturesSeveral silica phases are found in the opaline rocks and they show different behaviours after thermal treatments. Hydrothermal and sedimentary microcrystalline opal rocks were studied by means of X-ray diffraction and infrared absorption techniques. The measurements were carried out firstly on natural powdered samples and later on annealed samples at 1.050ºC for 24 hours. The purpose of this study is to ascertain which silica phases appear and to evaluate what changes take place as a consequence of thermal treatments. Most of the samples are constituted of opal CT. Opal CT is a crystalline stacked sequence of tridymite and cristobalite which displays different X-ray patterns mainly in the interval from 19º to 25º 2θ. Three basic types are defined according to the shape of the patterns in this interval: enlarged profiles (E), shoulder ...

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The origin and control of colour of white bentonites from the Aegean islands of Milos and Kimolos, Greece

Cited by 42 publications

References 28 publications

Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Formation and Growth of Smectites In Bentonites: A Case Study From Kimolos Island, Aegean, Greece

Comparative Study of the Mobility of Major and Trace Elements During Alteration of an Andesite and a Rhyolite to Bentonite, in the Islands of Milos and Kimolos, Aegean, Greece

Caracterización y respuesta al tratamiento térmico de rocas silíceas opalinas

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