Gemmological Characteristic of Brown Sapphire from Guinea, Africa
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摘要: 以非洲几内亚褐色蓝宝石为研究对象，利用激光拉曼光谱仪、红外光谱仪、激光剥蚀等离子质谱仪及显微紫外-可见光谱仪系统探究其宝石学特征。研究表明，非洲几内亚蓝宝石主要呈褐色、少量为绿色，抛磨成0.4 mm薄片后显红褐色且色带较发育。放大观察结合拉曼光谱测试发现，蓝宝石内部含有大量包裹体且以针状包裹体居多，含有硬水铝石、金红石、黄铁矿、磁铁矿、赤铁矿、锐铁矿等。红外光谱显示明显的1 990、2 123、2 912 cm-1和3 033 cm-1处与硬水铝石相关的O-H振动峰，指示其未经过热处理。激光剥蚀等离子质谱仪测试显示几内亚褐色蓝宝石中微量元素Fe、Ti、Cr含量较高，深色色带与浅色色带间的Fe、Ti等微量元素含量差异较大，与深色色带内部更为富集针状包裹体有关, 根据浅色色带处Fe/Ti浓度比＞10，推测为玄武岩型蓝宝石。紫外-可见吸收光谱显示由Fe3+导致的377、387、450 nm处吸收峰，与Cr3+离子有关的556 nm处吸收宽带以及693 nm处吸收锐锋，综合说明几内亚褐色蓝宝石体色主要为Cr3+导致红色，内部含有的大量褐色包裹体导致整体呈褐色。Abstract: The gemmological characteristics of sapphire from Guinea, Africa were investigated by laser Raman spectrometer, Fourier transform infrared spectrometer(FTIR), laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS) and micro-ultraviolet-visible spectrometer(UV-Vis). The analytical results show that sapphires from Guinea, Africa are mainly brown, with a minor contribution of green colour. After polishing into 0.4 mm slices, they show a reddish brown colour with obvious colour bands. Magnified observation showed that there are a lot of inclusions in sapphire and most of them are needle-like inclusions. Combined with Raman spectrum test results, it shows diaspore, rutile, pyrite, magnetite, hematite, anatase and other inclusions. The infrared spectra show obvious O-H vibration peaks related to diaspore at 1 990, 2 123, 2 912 cm-1and 3 033 cm-1, indicating that the sapphires were not heated. The contents of Fe, Ti and Cr in brown sapphires from Guinea are high. Fe, Ti and other trace elements between dark and light colour bands are quite different, which may be related to the enrichment of many inclusions in the dark colour band. According to the Fe/Ti ration(more than 10) in the light colour zone, brown sapphires from Guinea can be inferred as basaltic type. The UV-Vis absorption spectra show 377, 387 nm and 450 nm absorption peaks caused by Fe3+, and 556 nm absorption broad band and 693 nm absorption sharp front related to Cr3+ ions. The red body colour of brown sapphire is mainly caused by Cr3+, and the overall brown colour is caused by a large number of brown inclusions in the interior.
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Keywords:
- brown sapphire /
- gemmological characteristic /
- chemical composition /
- colour origin /
- Guinea
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图 1 非洲几内亚褐色蓝宝石样品
a.非洲几内亚蓝宝石原石；b.褐色弧面型蓝宝石；c.具有星光效应褐色蓝宝石；d.绿褐色蓝宝石
Figure 1. Brown sapphire samples from Guinea, Africa
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图 2 非洲几内亚褐色蓝宝石部分薄片样品
a.样品H-1为浅红褐色；b.样品Y-A-2为深红色褐；c.样品Y-C-2为绿褐色
Figure 2. Some of the thin sections of brown samphire samples from Guinea, Africa
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图 3 非洲几内亚褐色蓝宝石样品内部包裹体
a, b, c.样品Y-C-2、H-1、Y-B-1中针状包裹体；d.样品H-1中矿物包裹体及红色、黄色浸染物；e.样品H-5中黄色包裹体; f.样品H-10中微细包裹体；g.样品H-1中多相包裹体；h.样品H-5中长管状包裹体
Figure 3. Inclusions of brown sapphire samples from Guinea, Africa
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图 4 非洲几内亚褐色蓝宝石样品的拉曼光谱
Figure 4. Raman spectra of brown sapphire samples from Guinea, Africe
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图 5 非洲几内亚褐色蓝宝石样品内部包裹体的拉曼光谱
样品H-6中金红石的拉曼光谱；样品H-1中黄铁矿及磁铁矿的拉曼光谱；样品H-4中硬水铝石的拉曼光谱；样品H-2中赤铁矿的拉曼光谱；样品H-5中锐钛矿的拉曼光谱
Figure 5. Raman spectra of inclusions of brown sapphire samples from Guinea, Africa
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图 6 非洲几内亚褐色蓝宝石样品的红外光谱
Figure 6. Infrared spectra of the brown sapphire samples from Guinea, Africa
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图 7 非洲几内亚褐色蓝宝石样品深浅色带中Fe、Ti、Cr、Th的含量对比
a.Fe含量；b.Ti含量；c.Cr含量；d.Th含量
Figure 7. Content comparison of Fe, Ti, Cr and Th in the dark and light bands of brown sapphire samples from Guinea, Africa
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图 8 非洲几内亚褐色蓝宝石样品浅色色带中Cr/Ga与Fe/Ti浓度比值关系
Figure 8. Cr/Ga and Fe/Ti concentration ratio in light colour zone of brown sapphire samples from Guinea, Africa
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图 9 非洲几内亚褐色蓝宝石的紫外-可见吸收光谱
a.红褐色蓝宝石样品H-5；b.绿褐色蓝宝石样品Y-C-2
Figure 9. UV-Vis absorption spectra of brown sapphire from Guinea, Africa
表 1 非洲几内亚蓝宝石样品的常规宝石学特征
Table 1 Conventional gemmological characteristics of sapphire samples from Guinea, Africa
样品号 颜色 透明度 折射率 相对密度 紫外荧光 内部特征 LW SW H-1 红褐色 微透明 1.762~1.770 4.03 微红色 惰性 六方角状色带，黑色包裹体 H-2 褐色 不透明 1.761~1.769 3.93 惰性 惰性 色带，固体包裹体 H-3 褐色 不透明 1.763~1.771 3.97 惰性 惰性 六方角状色带、黄色杂质 H-4 褐色 不透明 1.762~1.770 3.97 惰性 惰性 色带，固体包裹体 H-5 褐色 不透明 1.762~1.770 3.95 惰性 惰性 六方角状色带，裂隙，固体包裹体 H-6 褐色 不透明 1.763~1.771 3.94 微红 惰性 裂隙，裂理，固体包裹体 H-7 褐色 微透明 1.763~1.771 3.98 微红 惰性 裂理，固体包裹体 H-8 褐色 不透明 1.762~1.770 3.98 惰性 惰性 色区，裂理，固体包裹体 H-9 褐色 不透明 1.763~1.771 3.96 惰性 惰性 六方角状色带，固体包裹体 H-10 褐色 不透明 1.762~1.770 3.96 惰性 惰性 色区，固体包裹体 Y-A-1 褐色 不透明 1.763~1.771 4.04 惰性 惰性 角状色带，固体包裹体 Y-A-2 褐色 不透明 1.763~1.771 3.98 惰性 惰性 平行色带，固体包裹体 Y-B-1 褐色 不透明 1.762~1.770 3.99 微红 惰性 角状色带，固体包裹体 Y-B-2 褐色 不透明 1.762~1.770 3.96 惰性 惰性 角状色带，固体包裹体 Y-C-2 绿色-褐色 半透明 1.763~1.771 3.99 惰性 惰性 色区, 裂理, 固体包裹体 
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表 2 非洲几内亚蓝宝石样品的化学成分
Table 2 Chemical compositions of brown sapphire samples from Guinea, Africak
/10-6 样品号 Fe Ti Cr Ga Mg V Nb Hf Ta Pb Th H-1-1(深) 3 515 1 269 761 99 47 70 0.39 0.06 0.50 11.83 36.13 H-1-2(深) 4 130 946 1 130 101 27 82 0.52 0 0.13 - 0.60 H-1-1(浅) 2 580 69 899 95 15 45 0 0.06 0 2.10 6.62 H-1-2(浅) 2 981 103 896 99 - 55 - 0.06 0.04 1.52 11.40 H-3-1(深) 7 003 2 071 1 179 143 101 52 2.42 0.18 3.82 1.54 4.64 H-3-2(深) 5 249 1 519 1 670 110 35 44 3.76 0 2.84 16.57 46.28 H-3-1(浅) 3 674 40 1 620 97 - 31 0 0 0 - - H-3-2(浅) 4 834 94 1 713 93 45 40 1.39 0.23 0 52.21 2.77 H-5-1(深) 7 454 880 1 176 120 30 58 0.23 0 0.35 10.66 24.32 H-5-2(深) 6 214 517 1 323 120 31 54 0.44 - 1.77 4.31 10.79 H-5-1(浅) 5 859 37 1 193 103 25 44 0 0 0 5.19 0.87 H-5-1(浅) 5 363 106 1 229 113 14 45 0.07 0 0 - 1.06 H-8-1(深) 7 055 1 151 1 083 143 52 80 1.88 0.06 2.60 17.32 47.63 H-8-2(深) 6 047 1 026 1 020 141 56 76 0.90 0.12 0.97 12.36 35.04 H-8-1(浅) 5 869 79 1 189 131 45 66 0 0 0.06 - 0 H-8-2(浅) 5 536 109 1 646 127 22 69 0 0 0.02 - 0.04 Y-A-1-1(深) 3 506 2 503 1 115 108 73 58 6.86 0.08 36.67 6.62 18.70 Y-A-1-2(深) 4 364 2 383 1 236 103 81 63 12.36 0 34.02 24.64 70.72 Y-A-1-1(浅) 2 187 60 1 372 93 20 41 0.05 0.09 0.32 - 0.55 Y-A-1-2(深) 1 833 154 1 763 102 25 53 1.51 0 17.85 1.72 3.96 Y-B-1-1(深) 1 767 2 354 1 288 112 40 72 4.17 - 2.06 31.72 93.38 Y-B-1-2(深) 1 406 1 674 1 510 120 37 69 2.03 1.13 2.77 9.08 28.65 Y-B-1-1(浅) 1 097 361 1 281 105 35 60 1.75 0.18 1.35 16.49 50.32 Y-B-1-1(浅) 1 573 500 1 566 108 - 69 0.69 0 1.86 2.38 7.36 Y-C-2-1(褐) 6 811 89 - 67 32 13 0 0.09 0 - 0.09 Y-C-2-1(褐) 6 837 87 - 79 14 14 0.11 0 0 0.99 0.08 Y-C-2-1(绿) 6 449 24 - 75 21 13 0 0 0 0.30 0 Y-C-2-1(绿) 5 832 35 - 65 27 12 0.06 0 0 0.61 0.06 注：“—”为检测限以下
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