Hydrothermal crystallization of silica gel

Oehler, John H.

doi:10.1130/0016-7606(1976)87<1143:hcosg>2.0.co;2

Cited by 136 publications

(65 citation statements)

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“…The presence and interrelationship of the crystalline and microcrystalline quartz suggest a fine to coarse crystallization sequence. Such a sequence was found in crystallization from colloidal silica gel (Oehler, 1976) and in natural cataclasites (Stel, 1981;Stel & Lankreyer, 1994).…”

Section: B Fracture and Diffusional Mass Transfermentioning

confidence: 95%

Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands

Needham¹

2004

Geol. Mag.

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-A study of the décollement zones in the Moffat Shale Group in the Ordovician Northern Belt of the Southern Uplands of Scotland reveals a progressive sequence of deformation and increased channelization of fluid flow. The study concentrates on exposures of imbricated Moffat Shale on the western coast of the Rhins of Galloway. Initial deformation occurred in partially lithified sediments and involved stratal disruption and shearing of the shales. Deformation then became more localized in narrower fault zones characterized by polyphase hydrothermal fluid flow/veining events. Deformation continued after vein formation, resulting in the development of low-temperature crystal plastic microstructures and further veining. Late-stage deformation is recorded as a pressure solution event possibly reflecting the cessation of slip on these faults as the slice became accreted. Most deformation can be ascribed to SE-directed thrusting and incorporation of the individual sheets into the Southern Uplands thrust stack. Later sinistral shear deformation, not observed in overlying turbidites, is also localized in these fault zones. The study reveals the likely structures formed at levels of an accretionary prism deforming under diagenetic to low-grade metamorphic conditions.

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Section: B Fracture and Diffusional Mass Transfermentioning

confidence: 95%

Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands

Needham¹

2004

Geol. Mag.

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“…The opal-A in silica sinters instead develops cristobalite but not tridymite stacking (D. White, oral communication, August 1987). Other near-surface systems with hot circulating water could transform directly from opal-A to quartz (Oehler 1976). …”

Section: S-mentioning

confidence: 99%

A preliminary comparison of mineral deposits in faults near Yucca Mountain, Nevada, with possible analogs

Vaniman¹,

Bish²

1988

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“…Sin embargo, no todas las formas esféricas mencionadas en la literatura tienen las mismas características ni corresponden a las mismas causas. En este estudio se ha desechado todos aquellos datos existentes sobre formas esféricas que poseían tamaños superiores a 1 u, Yque han sido interpretadas como restos de algas o bacterias (La Berge, 1973;Fairchild et al, 1973;Horodyski y Donalson, 1983) o como productos de la precipitación inorgánica de sílice amorfa por cristalización esferulítica (Oehler, 1976;Herzig et al, 1988). Considerando el entorno de tamaño de las microesferas anteriormente descritas y sus características, hay también interpretaciones que aluden a un origen orgá-nico o inorgánico (Fox y Syren, 1983), que es la disyuntiva que se nos plantea en este estudio.…”

Section: Discussionunclassified

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Bustillo¹

1995

Estud. geol.

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RESUMENUn estudio mediante MEB de silcretas miocenas opalinas formadas por silicificación de playas en un ambiente de «playa-lake» pone de manifiesto la existencia de una nueva microestructura de ópalo CT. Esta microestructura denominada en general fibrosa, se manifiesta por la presencia de multitud de fibras, filamentos o varillas formadas por la alineación de microesferas o microhemisferas que presentan un diámetro entre 0, l Y 0,2 1.1. Las fibras, filamentos o varillas tienen formas variables: rectas, curvadas, onduladas y «en horquilla», y presentan longitudes de hasta 10 11, aunque podrían existir longitudes mayores. La disposición organizada de las microesferas en filamentos o fibras, constituyendo la masa general del ópalo, y su parecido con microestructuras opalinas que han sido formadas por influencia bacteriana, hacen considerar esta hipótesis, aunque no se puede descartar totalmente un origen inorgánico por silicificación de sepiolita. Palabras clave: Microesferas, fihas, Opa/o CT, bacterias, si/cretas.ABSTRACT Electron microscope observations of opaline silcretes found in the playa of a miocene shallow lake reveal new opal CT microstructures. These microstructures are made up of fibres, filaments or rods, which are formed, in tum by coalesced microspheres or microhemispheres (0,1-0,2 11 diameter). They are up to 10 11 in length although larger ones could exist. They are straight, bent, wavy or even hairpin shaped. These microstructures comprise part of the opaline mass of the silcretes and are very similar to both neogenic opaline structures which are formed by bacterial intluence and to silicified biofilms. Therefore microbial mediation could exist in the genesis of this opal CT, although a possible inorganic origin by silicification of sepiolite is also considered.

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Hydrothermal crystallization of silica gel

Cited by 136 publications

References 0 publications

Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands

Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands

A preliminary comparison of mineral deposits in faults near Yucca Mountain, Nevada, with possible analogs

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