Preliminary Study on Gemmological Characteristics and Genesis of Andesine from Guyang,Inner Mongolia

The chemical compositions and mineral structures of the placer type gem-quality andesine samples from Guyang County, Inner Mongolia, are preliminarily studied by using the XRD, EPMA, LA-ICP-MS.The results show that the unit cell parameters of the and esine samples from Guyang are：a_o=0.8167nm, b_o=1.2811nm, c_o=0.7109nm, α= 93°43', β=116°16', γ=89°58'.The chemical formulas of the two representative samples（G-1, G-2） are respectively K_0.03Na_0.51Ca_0.44Al_1.39Si_2.60O₈ and K_0.03Na_0.50Ca_0.45Al_1.40Si_2.59O₈, and the end-member fomulas are respectively Ab₅₂An₄₅Or₃ and Ab₅₁An₄₆Or₃, where the Eu is positive anomalies and the light rare earth elements are more enriched than the heavy rare earth elements.Through the △2θ（131-1 \overline31）=1.91, the order degree is 0.5 and the formation temperature is about 700℃ of the samples, which indicates that the andesine samples from Guyang may come from the volcanic or plutonic environment with medium-high temperature.