辽宁海城析木玉中的矿物包裹体组合及其指示

Mineral Inclusion Assemblage and Its Indication in Simu Jade in Haicheng, Liaoning Province

  • 摘要: 析木玉出产于辽宁省海城市孤山镇瓦子沟村,是一种质地普遍细腻的优质黄绿色透闪石质玉,目前对其成因及产地标型特征的研究较为薄弱。本研究使用超景深显微镜和拉曼光谱,对50块具有代表性外观的析木玉原生矿样品的矿物包裹体进行了观察测试。结果显示,在析木玉中出现频率较高且外观独特的棒状绿帘石、粗晶透闪石、撕裂状磁黄铁矿、石墨包裹体及其风化白皮的外部特征具有一定的产地指示意义。棒状绿帘石呈集群状分布,暗绿色,单个颗粒形态为一头大、一头小的棒状,长度约为2~5 mm;粗晶透闪石多呈帚状、束状,分布在细腻的玉肉之中,无色,透明度较高,单个颗粒纤维长度可达厘米级,反射光下可见解理面闪光;撕裂状磁黄铁矿多出现在“老玉花”这一小品种玉料中,呈散点状或条带状分布,淡黄褐色,金属光泽,有弱磁性,与“老玉花”玉料特征的蓝青色玉肉结合形成了独特外观;石墨在样品中出现比例达90%以上,远高于其他产地的黄绿色软玉,呈弥散状、条带状分布,黑色不透明,半金属光泽,单个颗粒大小悬殊,3~150 μm均有出现;风化白皮分布在玉料外围,颜色极白,厚度普遍在2 cm以上,矿物组成仍为透闪石,可能是海城地区较强的化学风化作用致外围透闪石颗粒间隙变大而变白。石墨的拉曼光谱特征显示析木玉的原岩为绿片岩相-角闪岩相变质大理岩,粗晶透闪石的存在说明析木玉为多期次成玉,磁黄铁矿则指示其形成于还原性地球化学环境。上述发现对于进一步探索各史前各文化遗址出土玉器的产地提供了重要线索。

     

    Abstract: Simu jade, a high-quality yellowish-green tremolite jade, is produced in Haicheng city, Liaoning Province and has a long utilization history. In this study, the mineral inclusions in 50 samples were analyzed using a digital microscope system and Raman spectroscopy. The results show that rod-like epidote, coarse-grained tremolite, torn pyrrhotite, graphite, along with weathered white crust are of geographical indication. The unique appearances and high frequency of occurrence are good indications of the origin of Simu jade. The Raman spectra of graphite inclusions indicate that the metamorphic facies of the original rock of Simu jade varies from greenschist facies to amphibolite facies. The esistence of coarse-grained tremolite indicates that the formation of Simu jade had gone through at least two stages. The pyrrhotite inclusions suggest that Simu jade was formed in a reductive geochemical environment. The aforementioned findings provide significant clues for the further exploration of the origin of jade artifacts unearthed from prehistoric sites in China.

     

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