A Non-destructive Measurement Method of Gem Jadeite Content in Jadeitite Based on Specific Gravity and X-ray Powder Diffraction
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摘要:
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3.30~3.24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 & #215;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。
Abstract: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 3.30-3.24 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 non-destructive 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%.
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表 1 四组不同相对密度样品的偏光显微镜下特征对比
Table 1. A comparison of the mineralogical features for the jadeitites with different relative densities observed using polarization microscope
样品按
相对密度
分组相对密度
(SG)
范围矿物结构特征 主要矿物 次要矿物 A组 >3.25 柱状交织结构、
柱状-纤维放射结构、
粒状结构硬玉
(98%~91%)钠长石，
方沸石B组 3.25~3.19 柱状交织结构、
纤维-柱状放射结构、
粒状结构、
交代结构硬玉
(91%~83%)钠长石，
方沸石，
钠云母等C组 3.19~3.10 粒状结构、柱状结构、
交代结构、
柱状放射结构硬玉、
硬玉-透辉石
(88%~68%)钠长石，
方沸石，
钠云母等D组 3.10~2.88 交代结构、
粒状结构、
柱状结构、
柱状放射结构硬玉、
硬玉-透辉石
(68%~37%)钠长石，
方沸石，
钠云母等注：测试单位为国土资源部珠宝玉石首饰管理中心深圳珠宝研究所。 
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表 2 各组典型样品的矿物质量分数与相对密度
Table 2. Mineral contents and relative density of the typical samples
样品分类 样品编号 矿物组成的质量分数(%) 原石样品
相对密度理论
相对密度硬玉 钠长石 沸石 钠云母 A组 38-① 97 2 1 0 3.301 3.302 17-① 96 2 2 0 3.298 3.291 34-1 94 3 3 0 3.294 3.277 3 95 3 2 0 3.283 3.284 24-① 94 3 3 0 3.279 3.277 35-① 93 3 4 0 3.265 3.266 27-1 91 5 4 0 3.259 3.248 3-2 91 4 5 0 3.251 3.2 平均值 94 3 3 0 3.279 3.275 B组 33 90 5 3 2 3.240 3.247 3-① 89 4 3 4 3.240 3.242 1-1 92 5 3 0 3.224 3.246 3-12 91 4 5 0 3.230 3.237 10-① 89 6 5 0 3.221 3.221 24-① 85 4 11 0 3.200 3.201 2-1 87 8 5 0 3.210 3.200 2-① 86 5 7 2 3.210 3.210 41-① 84 4 9 3 3.209 3.202 平均值 88 5 6 1 3.220 3.223 C组 3-16 86 10 4 0 3.185 3.195 26-① 84 6 10 0 3.178 3.178 35 84 9 7 0 3.170 3.184 34-① 85 11 4 0 3.164 3.167 33-1 80 9 10 1 3.152 3.155 18-① 84 14 2 0 3.150 3.149 3-13 68 4 25 3 3.137 3.130 3-13 76 6 18 0 3.123 3.123 平均值 81 9 10 1 3.153 3.154 D组 3-19 71 10 18 1 3.088 3.086 D5 67 6 25 2 3.074 3.066 D2 67 6 22 4 3.066 3.065 5-1 75 13 12 0 3.058 3.106 3-22 73 14 13 0 3.058 3.073 D3 66 8 25 1 3.050 3.049 D19 63 6 30 1 3.030 3.036 D20 54 6 40 0 3.020 2.971 D18 60 10 27 3 3.005 3.006 D1 47 12 37 4 2.910 2.912 平均值 64 9 25 2 3.036 3.037 注：① 硬玉岩的理论相对密度按照各单矿物的理论密度计算，各单矿物的理论密度为：硬玉3.33 ~3.31 g/cm3，沸石2.26 g/cm3，钠长石2.62 g/cm3，钠云母2.88 g/cm。② 测试单位：国土资源部珠宝玉石首饰管理中心深圳珠宝研究所。
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表 3 样品中单矿物的相对密度测试结果
Table 3. Analytical results of the specific gravities of different minerals in jadeitite samples
样品 各单矿物的相对密度 硬玉 白云母 钾长石 斜长石 黑云母 绿泥石 SG=3.28(块状) 3.33 2.88 2.60 2.64 2.86 2.84 SG=3.08(块状) 3.31 2.87 2.59 0 0 2.83 注：测试单位为河北廊坊峰泽源岩矿检测技术实验室。
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