Topic
Tridymite
About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.
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8 citations
TL;DR: In this article, X-ray and micro-structural observations are inferred to have formed as mixed tridymite/cristobalite reaction products, now reverted to quartz, accommodating offloading owing to the 38% extensional strain parallel to c.
Abstract: Cylindrical samples of polycrystalline quartz were fabricated by hot pressing of crushed Brazilian quartz at 1100 and 1200°C, then deformed in extension at 1200°C at a confining pressure of 300 or 350 MPa. After initial plastic yield, samples failed with sudden and total offloading. Samples could be reloaded in compression and deformed plastically to large strains. Microscopic examination showed extensional failure had occurred with the formation of ‘veins’, oriented normal to the extension direction, containing fibers of silica with their length and c crystal axes parallel to the extension direction. From X-ray and microstructural observations, these are inferred to have formed as mixed tridymite/cristobalite reaction products, now reverted to quartz, accommodating offloading owing to the 38% extensional strain parallel to c. Such rapid transformation and offloading can be compared to processes invoked to explain deep-focus earthquakes in appropriate rock types, but also to the slower formation of oriented, localized reaction products in crustal shear zones.
8 citations
TL;DR: In this paper, the authors derived a hypothetical structure for Type V clathrate hydrate, which is hexagonal, P6 3 mmc, with a = 12.19A and c = 19.91A.
Abstract: Crystallographic data for cubic Type II clathrate hydrate have been used to derive a hypothetical structure for Type V clathrate hydrate. The structures of Types II and V are related by different stacking arrangements of layers of six-membered rings of pentagonal dodecahedra, which make up the water framework. The structure of Type II has an... ABCABC... stacking sequence, whereas the structure of Type V has an... ABAB... arrangement. Hypothetical Type V is hexagonal, P6 3 mmc, with a = 12.19A and c = 19.91A. The general stoichiometry for Type V, assuming fully occupied cages, is 4X.8Y.68H 2 O(X:H 2 O = 1:17). Theoretical oxygen and guest molecule positions are given for the structure of the hypothetical Type V hydrate. The relationship between the structures of Types II and V are analogous to that of the silica polymorphs tridymite and cristobalite, and the layered clathrasils. The stability of Type V and the possibility of stacking disorder between Type II and V structures, as is found for the silica polymorphs, is discussed.
8 citations
TL;DR: A magnesian halotrichite from a fumarole deposit on the active andesitic volcano of White Island, New Zealand, occurs as the major component in the mixture halotricite, with accessory gypsum, alunite, anhydrite, quartz, cristo-balite, and tridymite.
Abstract: A magnesian halotrichite [(Fe0.63Mg0.37).Al2(SO4)4.22H2O] from a fumarole deposit on the active andesitic volcano of White Island, New Zealand, occurs as the major component in the mixture halotrichite—H2S04-H20—alunogen, with accessory gypsum, alunite, anhydrite, quartz, cristo-balite, and tridymite. Optical, physical, and chemical data are given for the halotrichite. K :Na ratios in the alunite (85K:15Na) and in the solution (28K:72Na) show equilibrium between the salt and solutions.
8 citations
TL;DR: In this article, a three-dimensional structure model based on X-ray computed tomography (CT) was used to investigate the porosity of silica bricks, and the results showed that porosity was high but consisted mainly of interconnected pores, with a very small proportion of closed pores.
8 citations