内蒙固阳中长石的宝石学特征及成因初探

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

利用XRD,EPMA,LA-ICP-MS等测试分析技术初步研究了内蒙古固阳县产出的砂矿型宝石级中长石样品的化学成分与矿物结构,结果表明,固阳中长石样品的晶胞参数为:ao=0.816 7 nm,bo=1.281 1 nm,co=0.710 9 nm,α=93°43′,β=116°16′,γ=89°58′;其中具代表性的2块样品G-1与G-2的化学分子式分别为:K0.03Na0.51Ca0.44Al1.39Si2.60O8和K0.03Na0.50Ca0.45Al1.40Si2.59O8,其端员分子式分别为Ab52An45Or3和Ab51An46Or3,轻稀土元素较重稀土元素富集,整体上呈现Eu的正异常。固阳中长石样品中Δ2θ(131-131)=1.91,其有序度为0.5,形成温度约为700℃,这表明固阳中长石可能形成于一种中高温火山岩或深成岩环境。

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 andesine samples from Guyang are： ao=0.8167nm,bo=1.2811nm,co=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 K0.03Na0.51Ca0.44Al1.39Si2.60O8 and K0.03Na0.50Ca0.45Al1.40Si2.59O8 , and the end-member fomulas are respectively Ab52 An45 Or3 and Abst An46 Or3, where the Eu is positive anomalies and the light rare earth elements are more enriched than the heavy rare earth elements. Through the Δ2θ（131--131）=1. 91,the order degree is 0.5 and the formation tem- perature 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.