The role of water in the synthesis of glaucophane
The role of water in the synthesis of glaucophane
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DOI：
10.2138/am.2006.2014
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发表时间：
2006-07
影响因子：
3.1
通讯作者：
D. Jenkins;J. Corona
中科院分区：
文献类型：
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作者：
D. Jenkins;J. Corona
在2.5GPa和750 °C条件下，研究了水含量和固体起始混合物组成对蓝闪石[Na_2 Mg_3Al_2Si_8 O_（22）（OH）_2]形成的影响。角闪石显然是理想的蓝闪石组合物，证实了电子探针分析，通过处理氧化物或氧化物-氢氧化物的混合物与散装水含量为4.5重量%的持续时间约400小时，在多个治疗间歇研磨。这种含水量是必要的，以允许角闪石的生长，同时防止片状硅酸盐的干预，这在本研究中被确定为蛭石。为了使角闪石产率最大化，由于低水含量降低了合成过程的反应速率，需要间歇研磨的多次处理。在2.5 GPa和750 °C下，在log[aMg（OH）+/aH+]与log[（aNa +）（aAlSiO+）]空间中计算滑石、硬玉和蓝闪石的溶解度曲线，表明蓝闪石在没有硬玉或滑石共存的情况下具有非常窄的稳定域。这个图可以用来说明蛭石相对于蓝闪石的生长不是亚稳性的问题，而是水的活性的问题。
Abstract Syntheses have been done at 2.5 GPa and 750 °C to examine the effects of varying the water content and composition of the solid starting mixture on the formation of glaucophane [Na2Mg3Al2Si8O22(OH)2]. Amphiboles of apparently ideal glaucophane composition, confirmed by electron microprobe analyses, were obtained by treating oxide or oxide-hydroxide mixtures with bulk water contents of 4.5 wt% for durations of about 400 h in multiple treatments with intermittent grindings. This water content is necessary to permit growth of amphibole while preventing the intervention of a sheet silicate, which was identified in this study as vermiculite. To maximize amphibole yields, multiple treatments with intermittent grinding are needed on account of the low water contents that reduce the reaction rate of the synthesis process. Calculation of the solubility curves of talc, jadeite, and glaucophane in log[aMg(OH) +/aH+] vs. log[(aNa +)(aAlSiO₄-)] space at 2.5 GPa and 750 °C shows that glaucophane has a very narrow field of stability without coexisting jadeite or talc. This same diagram can be used to illustrate that the growth of vermiculite relative to glaucophane is not an issue of metastability but of the activity of water.