基于相对密度和X射线粉晶衍射技术测定硬玉岩中硬玉的含量

A Non-destructive Measurement Method of Gem Jadeite Content in Jadeitite Based on Specific Gravity and X-ray Powder Diffraction

硬玉岩能否命名为宝石级＂翡翠＂,其硬玉的含量是关键参数,目前测量岩石中矿物质量分数的方法多为有损分析,难以应用于珠宝玉石检测中。本文基于硬玉岩矿物组成及其质量分数的变化,建立了一种通过测量硬玉岩相对密度获得硬玉质量分数的无损分析方法。对186件相对密度在3.30~2.88之间的硬玉岩样品采用静水称重法测试,根据相对密度范围进行分组,利用X射线粉晶衍射、人工重砂分析、电子探针、红外光谱、拉曼光谱等技术确定硬玉岩的主要矿物及其质量分数,进而统计分析硬玉质量分数与硬玉岩相对密度的线性关系。研究表明：硬玉岩的主要矿物为硬玉和杂质矿物钠长石、方沸石。随着硬玉的质量分数（wA）下降,钠长石、方沸石质量分数增加,硬玉岩实测相对密度（SG）发生相应变化,两者的线性方程为wA=1.3454×SG-3.4531（相关系数为0.9814）,线性关系良好。由于本方法的硬玉岩实测相对密度近似等于理论相对密度,即可通过测量相对密度获得硬玉的质量分数,这种无损测试方法适用于相对密度在3.3~3.0,硬玉含量在95%~60%,硬玉与钠长石的质量分数之和在90%~97%之间的硬玉岩样品。

The key parameter to determine whether jadeitite can be named gem grade jadeitite ‘jadeite jade’or not is the content（ the mass fraction） of jadeite in jadeitite. So far,most methods to determine the mass fraction of mineral in rock are destructive, which is not suitable in gem detection. Based on the changes of mineral composition and mass fraction of mineral in jadeitite,a non-destructive method by measuring the relative density of jadeitite was established in order to get the mass fraction of jadeite. By Static Water Density Method,186 pieces of jadeitite samples with relative densities of 3. 30-2. 88 were divided into groups according to different densities.The main mineral composition and mass fraction of minerals in jadeitite were analyzed by X-ray Powder Diffraction,Manual Heavy-sand Analysis,Electron Probe Microanalysis,Infrared Spectrometry and Raman Spectrometry. The linear relationship between the mass fraction of jadeite and the relative density of jadeitite was statisticstically analyzed. Results show that the main minerals in jadeitite are jadeite,albite,and analcite. As the mass fraction（wA） of jadeite decreases,those of albite and analcime increase,and the measured specific gravities（ SG） of jadeitite change accordingly. The relationship between them is wA= 1. 3454 SG-3. 4531（ r = 0. 9814）,showing a good linear dependence relation. Because the measured specific gravity of jadeitite is approximately equal to the theoretical one,mass fraction of jadeite is obtained by measuring the specific gravity of jadeitite. This nondestructive method applies to jadeitite with a specific gravity of 3. 3-3. 0,jadeite content of 95%-60%,and sum mass fractions of jadeite and albite of 90%-97%.