X-site vacant Al-tourmaline: a new synthetic end-member
X-site vacant Al-tourmaline: a new synthetic end-member
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X位点空置铝电气石：一种新的合成端元
DOI：
10.1127/0935-1221/2001/0013-0521
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发表时间：
2001
影响因子：
2.1
通讯作者：
W. Schreyer
中科院分区：
文献类型：
--
作者：
Ulrich Wodara;W. Schreyer
作为电气石分类的缺失环节，在4-40 kbar、450-700 °C的PT范围内，在Al 2 O3-B2 O3-SiO2-H2O（ABSH）系统中由三种不同的起始成分合成了一种X位空位的橄榄石类似物，但从未作为单相产物;蓝绿硫铁矿与石英或蓝绿硫铁矿-OH是共存的固体。含有100%过量B2 O3的起始材料产生具有与合成过量硼橄榄石类似的异常低的电池参数的Al-电气石。电子探针分析确实显示了过剩的硼超过经典的3.0每分子式单位，这是与硅的不足。富铝电气石的晶胞体积a与四面体硼含量呈负线性相关。在20 kbar，600 ℃下获得的合成Al-电气石的初步结构式为：（□0.96 Na 0.004）Al 3（Al 5.83 Si 0.19）[Si 4.49 B 1.51 O 18]（BO 3）3（OH）3.21 O 0.79。
少量Na杂质可能是由于NaCl压力电池的污染，八面体Si是假设的。如果过量的Si被认为是由于分析误差，则会产生其他呈现八面体空位的假设公式。由于电气石的各种结构位点中的阳离子都不超过理论值的50%，因此可以将以下公式定义为理想化的Al-电气石端元：□ Al 3 Al 6 [Si 6 O 18]（BO 3）3 O2（OH）2。在自然界中，这种X位空位富铝电气石预计将出现在富铝和（镁，铁）-，钙和碱的热液系统或围岩蚀变的产品，或在其变质等价物，如dumortierite石英岩。内华达州热液系统中异常富铝的复杂电气石含有高达56mol%的上述端元以及黑云母、富铁矿和透辉石组分。
这份文件是在意大利贝加莫举行的第八届欧洲货币政策小组会议上提出的（2000年4月）。
As a missing link of the tourmaline classification, an X-site vacant analogue of olenite was synthesized from three different starting compositions in the system Al2O3-B2O3-SiO2-H2O (ABSH) over the PT-range 4–40 kbar, 450–700 °C, however never as a single phase product; dumortierite with either quartz or with jeremejevite-OH were the coexisting solids. The starting materials containing 100% excess B2O3 produced an Al-tourmaline with exceptionally low cell parameters similar to those of synthetic excess-boron olenite. Electron microprobe analyses indeed show a surplus of boron over the classical 3.0 per formula unit, which is linked with a deficiency in silicon. There is a negative linear correlation between the cell volume a of Al-rich tourmalines and their tetrahedral boron contents. A preliminary structural formula of the synthetic Al-tourmaline obtained at 20 kbar, 600 °C is: (□0.96 Na0.004) Al3 (Al5.83 Si 0.19) [Si4.49 B 1.51 O18] (BO3)3 (OH)3.21 O0.79.
The small Na impurity is probably due to contamination from the NaCl pressure cell, octahedral Si is hypothetical. If the excess Si is considered to be due to analytical error, other hypothetical formulae exhibiting octahedral vacancies result. As none of the cations in the various structural sites of the tourmaline exceed 50% of the theoretical value, the following formula can be defined as idealized Al-tourmaline end-member: □ Al3 Al6 [Si6O18] (BO3)3 O2 (OH)2. In nature, such X-site vacant Al-rich tourmalines would be expected to occur in Al-rich and (Mg, Fe)-, Ca- and alkali-free products of hydrothermal systems or of wall-rock alterations, or in their metamorphic equivalents such as dumortierite quartzites. An unusually Al-rich, complex tourmaline from a hydrothermal system in Nevada contains as much as 56 mol % of the above end-member together with schorl, foitite and rossmanite components.
This paper was presented at the EMPG VIII meeting in Bergamo, Italy (April 2000)