一种钙铁质锰铝榴石的宝石矿物学特征

Gemmological and Mineralogical Characteristic of Calcareous and Iron Spessartine

  • 摘要: 由于不同石榴石品种的经济价值不同,为了给来自山西交城界河口群铅锌矿中发现的一种褐橙色石榴石定名,选取4块样品进行宝石矿物学特征探究。镜下观察发现,石榴石裂隙发育,裂隙内充填有少量石英。利用X射线粉末衍射仪,得到石榴石的晶胞参数介于Mn3Al2Si3O12与(Mn,Ca)3Al2Si3O12之间。运用电子探针对该石榴石进行主量元素组成分析,确定其为一种少见的混合型石榴石(Mn1.53Ca0.81Fe0.61Mg0.03)(Al1.90Fe0.13Cr0.01)Si2.98O12,其平均组分为Sps51.29Alm20.43Grs20.40Adr6.46Prp1.01Uvt0.41,出现了铝质系列石榴石与钙质系列石榴石之间的类质同象替代,并且钙铝榴石含量超过20%。根据Sps-Alm-Grs投影确定其名称为钙铁质锰铝榴石。

     

    Abstract: Since the different economic values between different varieties of garnet, the authors selected 4 brown-orange garnet samples and studied their gemmological and mineralogical characteristics,which occurred in the Jiehekou Group of Jiaocheng area, Shanxi Province.The garnets were accompanied with Pb-Zn ore.Through thin section observation, the cracks were filled with quartz, and developed widely through the garnet grains.XRD results showed that the crystal lattice parameters of the samples were between Mn3Al2Si3O12 and (Mn, Ca)3Al2Si3O12.Major element data obtained by EPMA, showed the complex composition of the garnet is rare, (Mn1.53Ca0.81Fe0.61Mg0.03)(Al1.90Fe0.13Cr0.01)Si2.98O12, and the average component is Sps51.29Alm20.43Grs20.40Adr6.46Prp1.01Uvt0.41, with the isomorphic substitution between pyralspite and ugrandite.The content of Grs is more than 20%.The subspecies name is determined as calcareous and iron spessartine by Sps-Alm-Grs diagram plotting.

     

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