Gemmological and Mineralogical Characteristic of Calcareous and Iron Spessartine

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, (Mn_1.53Ca_0.81Fe_0.61Mg_0.03)(Al_1.90Fe_0.13Cr_0.01)Si_2.98O₁₂, and the average component is Sps_51.29Alm_20.43Grs_20.40Adr_6.46Prp_1.01Uvt_0.41, 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.