We have investigated the thermal expansion of 15 naturally occurring chemically diverse amphiboles utilizing high-temperature X-ray powder diffraction. As done in the first paper of this series on pyroxenes, volume-temperature data were analyzed using the physical Kroll and empirical Fei thermal expansion models. As in pyroxenes, orthorhombic amphibole end-members expand more than monoclinic ones, which is related to the greater kinking of the chains of tetrahedra permitted by the Pnma symmetry. In the case of chemically similar phases, increased Al in octahedral cation sites decreases expansion. Although the ranges of thermal expansion coefficients for amphiboles and pyroxenes are similar, expansion patterns are not the same. Amphiboles exhibit higher expansion along a*, but lower along b, just the reverse of that observed in pyroxenes. An exception to this is the data for pargasite, which shows higher expansion along the b axis due to the presence of Al in tetrahedral sites. Current data will be useful in modeling reactions involving amphiboles in both metamorphic and igneous environments.

中文翻译：

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闪石超群中矿物的热膨胀

我们利用高温 X 射线粉末衍射研究了 15 种天然存在的化学多样性闪石的热膨胀。正如本系列关于辉石的第一篇论文中所做的那样，使用物理 Kroll 和经验费热膨胀模型分析了体积温度数据。与辉石一样，斜方闪石末端成员比单斜体末端成员膨胀更多，这与 Pnma 对称性允许的四面体链的更大扭结有关。在化学相似相的情况下，八面体阳离子位点中铝含量的增加会降低膨胀。尽管闪石和辉石的热膨胀系数范围相似，但膨胀模式并不相同。闪石沿 a* 表现出更高的膨胀，但沿 b 表现出较低的膨胀，这与在辉石中观察到的正好相反。一个例外是 pargasite 的数据，由于四面体位点中 Al 的存在，它显示了沿 b 轴的更高膨胀。当前数据将有助于模拟涉及变质和火成岩环境中闪石的反应。