The term “demantoid”, first proposed in 1856 by the famous Finnish mineralogist Nils von Nordensheld, refers to a highly dispersed yellow-green mineral from the Central Urals placers. In 1874, it was found to be a gem variety of andradite garnet. “Horsetail” inclusions are considered a sign of the Ural type demantoid. Although these inclusions are large (visible to the naked eye), their diagnostics remains debatable: some researchers attribute them to byssolite (amphibole-asbestos), others consider them chrysotile. We investigated the horsetail inclusions in the Ural demantoids through various methods: optical microscopy, scanning electron microscopy (SEM), Raman spectrometry, X-ray powder diffraction, and thermal analysis. In most cases, “horsetail” inclusions in the Ural demantoid were represented by hollow channels and only the outcrops, on the demantoid surface, were occasionally filled with serpentine (established by SEM); in one case, magnetite was observed. Hollow canals were usually collected not in bundles, such as a “horsetail”, but in fans, sometimes curved into cones. The structure of the grains was spheroidal, sectorial, and sometimes had induction surfaces, which, to the periphery of the grain, were replaced by tubular channels assembled in a fan. The specifics of the growth of the “horsetail” inclusions of the demantoid grains can be explained by the decompression conditions that arose when the ultrabasites (a crust-mantle mixture) were squeezed upwards during collision.

中文翻译：

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乌拉尔翠榴石中的“马尾”内含物：生长形态

1856 年，著名的芬兰矿物学家 Nils von Nordensheld 首次提出“翠榴石”一词，指的是来自乌拉尔中部砂矿的高度分散的黄绿色矿物。1874 年，人们发现它是红石榴石的宝石品种。“马尾”内含物被认为是乌拉尔型翠榴石的标志。尽管这些内含物很大（肉眼可见），但它们的诊断仍然存在争议：一些研究人员将它们归因于斜闪石（角闪石-石棉），其他人则认为它们是温石棉。我们通过各种方法研究了乌拉尔翠榴石中的马尾包裹体：光学显微镜、扫描电子显微镜 (SEM)、拉曼光谱、X 射线粉末衍射和热分析。在大多数情况下，乌拉尔翠榴石中的“马尾”包裹体表现为空心通道，只有露头，在翠榴石表面，偶尔充满蛇纹石（由扫描电镜确定）；在一种情况下，观察到磁铁矿。空心运河通常不是成束收集，例如“马尾”，而是收集在扇形中，有时会弯曲成锥形。谷物的结构是球状的、扇形的，有时有感应表面，在谷物的外围，它被组装在风扇中的管状通道所取代。翠榴石颗粒的“马尾”包裹体生长的细节可以用超重基岩（壳幔混合物）在碰撞过程中向上挤压时产生的减压条件来解释。但在风扇中，有时会弯曲成锥形。谷物的结构是球状的、扇形的，有时有感应面，在谷物的外围，被组装在风扇中的管状通道所取代。翠榴石颗粒的“马尾”包裹体生长的细节可以用超重基岩（壳幔混合物）在碰撞过程中向上挤压时产生的减压条件来解释。但在风扇中，有时会弯曲成锥形。谷物的结构是球状的、扇形的，有时有感应面，在谷物的外围，被组装在风扇中的管状通道所取代。翠榴石颗粒的“马尾”包裹体生长的具体情况可以用超重基岩（壳幔混合物）在碰撞过程中向上挤压时产生的减压条件来解释。