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首页> 外文期刊>Spectrochimica acta, Part A. Molecular and biomolecular spectroscopy >A Raman, infrared and XRD analysis of the instability in volcanic opals from Mexico
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A Raman, infrared and XRD analysis of the instability in volcanic opals from Mexico

机译：拉曼，红外和XRD分析墨西哥火山蛋白石的不稳定性

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A series of natural volcanic opal samples with the destabilization phenomena from Mexican deposits (states of Queretaro and Jalisco) was investigated by Raman microprobe (RMP), infrared spectrometry and XRD analysis. These techniques show that at low and room temperatures the unaltered transparent opals may be transformed into destabilized white opals, which are a mixture of different polymorphs of tridymite and alpha-cristobalite with various degrees of crystallinity. We found systematic changes in frequencies of both the Raman and the infrared bands, caused by increasing regularities of bond-lengths and bond-angles Si-O-Si groups under the effect of stability. Micro-Raman spectrometry confirms that in the destabilized opal the principal mineral phases are MC (monoclinic ordered)- and MX (incommensurate monoclinic)-tridymites that are characterized by more structural order in comparison with other structural modification of this phase in unaltered opal (POn pseudo-orthorhombic disordered tridymite). XRD investigations show that in the sequence from unaltered to destabilized opal the position of principal maximum (4.30, 4.10 and 2.50 angstrom) shifts towards higher d-spacing. This XRD shifting to higher d-spacing can largely be explained by an increasing amount of tridymite stacking and unresolved superposition of cristobalite and tridymite reflections. The destabilization phenomena in volcanic opals is due to the structural ordering/disordering that is characterized mainly by the formation of the different tridymite polymorphs (MC and MX) in the destabilized opal-CT as well as the decreasing content of molecular water in the structure. (c) 2007 Elsevier B.V. All rights reserved.
机译：通过拉曼探针（RMP），红外光谱和XRD分析，研究了一系列天然火山蛋白石样品，这些样品具有墨西哥沉积物（克雷塔罗州和哈利斯科州）的失稳现象。这些技术表明，在低温和室温下，未改变的透明蛋白石可以转变为不稳定的白蛋白石，白蛋白石是鳞石英的不同多晶型物和α-方石英的不同结晶度的混合物。我们发现，在稳定作用下，由于键长和键角Si-O-Si基团的规则性增加，导致拉曼和红外波段的频率发生系统性变化。显微拉曼光谱法证实，在不稳定的蛋白石中，主要矿物相是MC（单斜晶有序）-和MX（不相称单斜晶）-三叠氮化物，与未经改变的蛋白石（POn假斜方晶状的无序鳞状晶状体）。 XRD研究表明，在从未改变到不稳定的蛋白石的顺序中，主要最大值（4.30、4.10和2.50埃）的位置朝着更高的d间隔移动。这种XRD向更高d间距的转变可以用大量的鳞石英堆积和方石英和鳞石英反射的未解决叠加来解释。火山蛋白石的失稳现象是由于结构有序/无序而造成的，其特征主要是在失稳的蛋白石CT中形成了不同的Tridymite多晶型物（MC和MX），以及结构中分子水含量的降低。 （c）2007 Elsevier B.V.保留所有权利。

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