热处理对山东昌乐蓝宝石产生的影响

Effect of Heat Treatment on Sapphire from Changle, Shandong Province

  • 摘要: 山东昌乐蓝宝石属于玄武岩型成因,由于其原石颜色较深,大部分蓝宝石需要进行热处理。本研究以天然山东昌乐蓝宝石样品为研究对象,采用红外光谱、拉曼光谱、紫外-可见吸收光谱、LA-ICP-MS等测试手段对其进行了宝石学特征、谱学特征、包裹体特征和化学元素等方面的分析,以此为基础系统地对山东昌乐蓝宝石样品进行不同温度的热处理,并分类总结该过程中样品的宝石学及谱学特征变化。山东昌乐蓝宝石样品的颜色整体较深,原石表面附着一层黑色熔融壳,裂隙处偶见次生铁质浸染,多色性明显。蓝宝石内包裹体种类及数量丰富,含单质硫、方解石、白云石、赤铁矿、透闪石、金红石、无定形碳、锆石等矿物包裹体,此外还存在罕见的定向排列包裹体和树枝状包裹体。样品的红外光谱指纹区主要特征峰为483、630 cm-1和514 cm-1,官能团区为不同方向上Ti-OH振动所引起的3 309 cm-1系列峰;拉曼光谱集中在100~800 cm-1,主要特征峰为247、380、417、577 cm-1和750 cm-1。LA-ICP-MS和电子探针测试结果显示,杂质元素中Fe的含量最高且变化范围较大,含量与颜色深浅变化成正比。Ti元素含量大多在300×10-6内,从中心到边缘呈降低趋势,黄绿色-蓝绿色样品中Ti含量偏低。在氧化环境下,对山东昌乐蓝宝石进行恒温时间不变、从低温到高温梯度的热处理。实验结果表明,蓝宝石样品外观整体亮度提高,具达碧兹结构的更为明显;包裹体发生杂质矿物熔融、重结晶和矿液减少后析晶等现象;红外光谱中官能团区3 309 cm-1系列峰随温度的升高逐渐变小或消失,指纹区630 cm-1处的特征吸收峰随温度升高逐渐增强且尖锐,认为此变化是鉴定玄武岩型蓝宝石的新型证据。以CIE1967-LAB色度学模型为基础,颜色量化后发现热处理后蓝宝石的明度值(L*)均大于热处理前,其饱和度(C*)和色调角(h°)的变化无明显规律且存在一定误差,仍需进一步研究。

     

    Abstract: The sapphire from Changle, Shandong Province belongs to the basalt type of genesis. Due to the dark colour of the rough stones, most of sapphires need to be heat-treated. In this study, the gemmological and spectral characterastics, inclusions and chemical compositions of sapphires from Changle, Shandong Province were studied using infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy and LA-ICP-MS.The sapphire samples were heat-treated at different temperatures in order to classify and summary the changes of gemmological and spectral characteristics during the heatment process. The main colour of sapphire from Changle, Shandong Province is deep, with black fused crusts attached to its surface, with occasional secondary ferriferous minerals in the fissure, and obvious pleochroism. The types and quantities of inclusions in sapphires are abundant, including mineral inclusions such as sulfur, calcite, dolomite, hematite, tremolite, rutile, amorphous carbon, zircon, etc. In addition, there are rare oriented regular inclusions and dendritic inclusions.The main characteristic peaks in the fingerprint region of the IR spectrum are 483, 630 cm-1 and 514 cm-1, and the functional group region is a series of 3 309 cm-1 peaks caused by Ti-OH vibration in different directions; the Raman spectrum is concentrated between 100 cm-1 and 800 cm-1, with the main characteristic peaks at 247, 380, 417, 577 cm-1 and 750 cm-1. The results of LA-ICP-MS and electron microprobe tests show that the content of Fe is the highest among the impurity elements and varied widely, with the content proportional to the colour shade. The content of Ti is mostly within 300× 10-6, with a decreasing trend from the center to the edges of the stones, and is low in the yellow-green to blue-green sapphire samples. In the oxidizing environment, the sapphires were heated with constant temperature time from low to high temperature gradient heat treatment. The experimental results show that the brightness of the sapphire samples is improved, and is more obvious in "Trapiche" sapphire samples; the inclusions have the phenomena of mineral melting and recrystallization; with the increase of temperature, the 3 309 cm-1series peaks in the functional group region in of IR spectra gradually become smaller or disappear, and the characteristic absorption peak at 630 cm-1 in the fingerprint region gradually increases and becomes sharp. The change of 630 cm-1 is considered as a new evidence for identifying basaltic sapphire. Based on the CIE1967-LAB chromatographic model, colour quantification reveals that the luminosity value (L*) of sapphires after heat treatment is all greater than those before heat treatment. The changes of saturation (C*) and hue angle (h°) have no obvious pattern and are subject to some errors, which still need further study.

     

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