Gemmological Characteristic of "Tanghe Jade" and Its Quality Evaluation
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摘要:
“唐河玉”主要产于太行山北端的唐河流域，在拒马河、易水河也有少量产出，该玉石的“籽料”主要由透闪石构成，颜色以白色、黄色、红色和黑色为主，偶尔伴有灰色、青色和绿色等次要色调。然而，杂质矿物的存在导致了该玉石质量呈现出一定程度的差异性。为了深入研究这一现象，本研究采取了实地勘查和市场调研相结合的方法，对采集到的“山料”及“籽料”样品进行了系统的宝石矿物学特征分析。在传统宝玉石研究方法的基础上(如折射率、相对密度、硬度以及显微观察和红外光谱分析)，本研究综合应用了现代分析技术，包括X射线衍射分析、电子探针分析和扫描电子显微镜镜分析，全面深入地探究“唐河玉”样品的矿物和结构组成。研究结果显示，“唐河玉”样品的折射率为1.56~1.61(点测法)，相对密度2.85~3.07，摩氏硬度6~7，表现出良好的油润度和宏观上的蜡状至油脂光泽。在偏光显微镜下观察，其主要矿物组成为透闪石，同时伴有碳酸盐矿物、石英、透辉石等杂质矿物。其中，透闪石呈柱状和纤维状变晶结构，其中纤维状变晶的纤维长度约为0.01~0.10 mm，交织形成复杂的微观纹理；而柱状变晶的粒度则在0.05×0.02 mm至1.00×0.15 mm，颗粒相互镶嵌，且杂质矿物不均匀地分布在纤维状透闪石之间。通过扫描电镜的二次电子成像技术有效地揭示了“唐河玉”样品中矿物颗粒的大小、形态和结晶程度。观察结果表明，部分透闪石颗粒以纤维放射状分布且相互交织，在小区域范围内的定向排列。这些颗粒之间排列紧密，部分显示出显微纤维交织结构。在局部范围内，纤维状的透闪石呈现出规则的排列，颗粒间交织紧密。整体上，规则排列的透闪石在非定向的穿插中形成整体结构，颗粒表面光滑平整，少数颗粒表面具有纵向纹理。此外，部分透闪石颗粒呈现出略具定向的分布特征，聚集形成宽窄不一的条带状集合体。石英颗粒则以自形-半自形的粒状形态穿插于透闪石之中，粒度大约为5 μm。结合电子探针分析和X射线粉末衍射测试结果显示“唐河玉”样品的主要矿物组成为透闪石，次要矿物有方解石、石英和透辉石。在钙质角闪石系列中，透闪石-阳起石的“唐河玉”样品Mg/(Mg+Fe2+)比值大于0.98，接近于透闪石端元的理论值1.0。“唐河玉”样品的红外光谱与透闪石的标准光谱峰位基本一致，主要表现在600~400 cm-1、800~600 cm-1、1 200~800 cm-1、3 750~3 600 cm-1等四个波段。其中，1 147、1 063、1 042、996、922 cm-1附近的尖锐吸收峰归因于Si-O-Si的反对称伸缩振动、O-Si-O的对称伸缩振动和反对称伸缩振动所致。而765、687、665、644 cm-1的吸收峰则是由Si-O-Si的对称伸缩振动引起。546、514、459、420 cm-1的吸收峰则由Si-O的弯曲振动及M-O的晶格振动造成。此外，在1 560~1 400 cm-1波段，部分样品显示出不同强度的吸收，这归因于碳酸盐矿物晶体结构中[CO3]2-的反对称伸缩振动和面外弯曲振动引起。基于上述研究成果，建立了以碳酸盐矿物质量分数为依据的“唐河玉”宝石学命名标准，具体分类如下：当碳酸盐矿物质量分数低于5%，且透闪石质量分数不低于95%时，命名为“透闪石玉”；当碳酸盐矿物质量分数在5%~40%，且透闪石质量分数在60%以上时，命名为“方解石-透闪石玉”或“白云石-透闪石玉”；当碳酸盐矿物质量分数不低于50%，且透闪石质量分数低于40%时，命名为“透闪石化大理岩”。鉴于“唐河玉”具有独特的“草花”纹理特征及其颜色、纹理和质地的丰富多样性，本研究将这些特性与“籽料”属性和唐尧文化进行了综合评估。在此基础上，通过宣传其深厚的文化和独特的美学价值，并依据玉石的品质进行市场定位，为“唐河玉”的进一步开发和应用提供了清晰的发展方向。
Abstract:"Tanghe jade", predominantly harvested from the Tanghe River basin in the northern Taihang Mountain range, is also output in modest quantities along the Juma and Yishui rivers. The primary colours of "Tanghe jade" are white, yellow, red, and black, complemented by secondary colours of gray, cyan, and green. The main mineral component of "Tanghe jade" is tremolite, however, the presence of impurity minerals lead to differences for its quality. In this paper, the methods of combining field investigation and market surveys, the gemmological and mineralogical characteristics of the"Tanghe jade"samples were analysed using conventional gemmological tests (eg.refractive index, relative density, hardness, microscopic observation and infrared spectroscopy), as well as XRD, EPMA, and SEM.The results show that the refractive index of "Tanghe jade" sample is 1.56 to 1.61 and the relative density is 2.85 to 3.07, while the Mohs hardness is between 6 and 7. The "Tanghe jade" is of moderate greasy luster, with wax-oily luster. Polarizing microscope observation results reveal that the predominant mineral component is tremolite, accompanied by impurities such as carbonates, quartz, and diopside. Tremolite exhibits a columnar-fibrous metamorphic texture, with some areas presenting a fibrous metamorphic structure. The fibers are mainly within the confines of 0.01-0.10 mm in length, intricately interlaced to create a tightly woven texture. Some samples exhibit columnar crystals, with grain sizes ranging from 0.05×0.02 mm to 1.00×0.15 mm. These crystals are intricately interlocked, creating a tessellated arrangement, and a minor concentration of impurity minerals is unevenly dispersed throughout the fibrous tremolite matrix.SEM results show that some tremolite particles are distributed in a fibrous, radiating pattern and interwoven together, exhibiting a directional arrangement within small areas. The particles are closely packed, with some displaying a micro-fibrous interlocking structure. Within localized domains, the fibrous tremolite is regularly arranged with closely interwoven particles. Over the entire area, the regularly arranged tremolite particles are interspersed in a non-directional manner. The surface of the tremolite particles is relatively smooth and flat, with a minority of particles exhibiting longitudinal textures. Furthermore, some tremolite particles exhibit the slightly directional distribution, aggregating into bands of varying widths to form collective aggregates. Quartz particles being automorphic form and semiautomorphic form, are interspersed in tremolite, with a particle size of approximately 5 μm. The EMPA and XRD results confirms that tremolite is the predominant mineral of "Tanghe jade", and subordinate minerals encompass calcite, quartz, and diopside. In the context of the tremolite-actinolite series within the calcic amphiboles, the sample's Mg/(Mg+Fe2+) ratio surpasses 0.98, converging on the theoretical end-member value of 1.0 for pure tremolite.The infrared spectra of "Tanghe jade" are basically consistent with standard spectral peaks of tremolite, mainly in 600-400 cm-1, 800-600 cm-1, 1 200-800 cm-1, and 3 750-3 600 cm-1. The distinct and sharp absorption bands near 1 147, 1 063, 1 042, 996 cm-1 and 922 cm-1 correspond to the antisymmetric stretching vibrations of the Si-O-Si linkages, as well as the symmetric and antisymmetric stretching vibrations of the O-Si-O bridges. The peaks at 765, 687, 665 cm-1 and 644 cm-1 indicate the symmetric stretching vibrations associated with Si-O-Si. Furthermore, the vibrations at 546, 514, 459, 420 cm-1 are attributed to the bending vibrations of Si-O bonds and the lattice vibrations involving M-O.Additionally, some "Tanghe jade"samples exhibit variable intensity absorptions in the 1 560-1 400 cm-1, which are caused by the antisymmetric stretching and out-of-plane bending vibrations of the carbonate [CO3]2- groups within the mineral's crystalline framework. Based on the above research, the gemmological designation criteria for "Tanghe jade" are established, differentiated by the mass fraction of carbonate minerals. The classification is as follows: (1) when the carbonate mineral mass fraction is below 5% and the tremolite mass fraction exceeds 95%, the material is aptly designated as "tremolite jade"; (2) when the carbonate mineral mass fraction ranging from 5% to 40% and tremolite mass fraction above 60%, the nomenclature is differentiated based on the carbonate composition as either "calcite-tremolite jade" or "dolomite-tremolite jade"; (3) when the carbonate mineral mass fraction reaches or exceeds 50% and the tremolite mass fraction falls below 40%, the material is termed "tremolite marble". By highlighting the distinctive of the pattern floral of "Tanghe jade", along with its vibrant colour palette and diverse textures, and integrating the cultural significance of the "pebbles"with the legacy of the Tang Yao civilization, the targeted promotion and quality-based market positioning of "Tanghe jade" can be strategically directed towards its enhanced development and utilization potential.
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Keywords:
- "Tanghe jade" /
- tremolite /
- gemmological characteristic /
- quality evaluation
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合成碳硅石，商业名称为“莫桑石”，因与天然钻石具有十分相似的宝石学属性，且市场价值远低于钻石，深受部分消费者的青睐。目前，已发现的碳化硅晶体结构有200多种[1], 其中主要的结构有纤锌矿结构、菱形结构和闪锌矿结构等；依据构型的不同特点，可以用数字和大写字母来表示和命名，其中最为常见的有3C-SiC、4H-SiC、6H-SiC和15R-SiC四种类型[2]。随着大众消费观念的变化，宝石级合成碳硅石凭借其净度高、色泽佳、佩戴效果美观、价格合适等诸多优势，逐步被更多的消费者熟知和接受，其市场需求持续提高[3]。此外，结合培育钻石的市场行情，反映出消费者对合成宝石的整体认可度正在提高，行业不再局限于传统的天然宝石，人工宝石如合成碳硅石因其成本优势和稳定的供应正逐渐成为市场新宠。行业内的不断创新，从原材料合成到宝石成品设计，整个产业链都在向更高质量、更多元化的方向发展。然而，针对合成碳硅石的研究特别是绿色调样品存在明显空缺，鉴于此，本文以绿色合成碳硅石样品为主要研究对象，测试分析其宝石学属性、谱学特征，以期更加丰富合成碳硅石相关的理论研究。
1. 实验及样品描述
1.1 测试方法
采用Nicolet iS10美国热电半衰减红外光谱仪对样品进行测试(反射法)，测试条件：扫描温度18~25 ℃，扫描范围4 000~400 cm-1，分辨率4 cm-1，扫描次数32次，电压85~265 V；采用Renishaw in Via型激光共焦显微拉曼光谱仪对样品进行测试，测试条件：激光器532 nm，光栅1 800 l/mm，50倍物镜，输出功率250~500 mW，最佳分辨率1 cm-1，曝光时间10 s，扫描信号叠加2次，测试范围100~4 000 cm-1；采用岛津UV-3600Plus型紫外-可见分光光度计对样品进行测试(反射法)。实验条件：狭缝宽度2 nm，扫描速度120 nm/min。
1.2 样品描述
本文研究的合成碳硅石样品主色调为绿色，表面存在一层碳质薄膜，因厚度超过3 cm，肉眼观察为黑色，透射光下颜色显示为深绿色，直径约为15 cm。对其进行切割、切磨、抛光后分别得到公主方型、弧面型以及集色带与管状包体于一体的薄片样品各一个，分别编号为SiC-3、SiC-2和SiC-1(图 1a-图 1d)。
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图 1 合成碳硅石原材料(a)，透射光下选区切块样品(b)，弧面型样品含明显白色管状包裹体(c)，公主方型样品显示明显的后刻面棱重影(d)，偏光镜下一轴晶干涉图(e)和薄片样品中黄绿色带及定向管状包裹体(f)Figure 1. (a) Raw material for sythetic moissanite; (b) selected slice sample under transmitted light; (c) cabochon samples with obvious white tubular inclusion; (d)square modified cut sample with a distinct back-faceted edge double shadow; (e) an axial crystal interferogram under a polarizer; (f) thin slice sample with yellow-green band and directional tubular inclusion2. 结果与讨论
2.1 基本特征
实验室测得合成碳硅石的折射率＞1.78，反射仪测定折射率变化范围为2.648~2.691，相对密度约为3.22 ± 0.02，抛光较好者呈亚金刚光泽(图 1c)，偏光镜下定向可见明显的一轴晶干涉图即黑十字及圆形干涉色圈(图 1e)，可见光吸收光谱蓝紫区可见一条吸收线。
合成碳硅石样品内部包裹体丰富，除光轴方向外，可见明显的后刻面棱重影(图 1d)、白色管状包裹体(图 1c)以及黄绿色带(图 1f)等。白色线(管)状包裹体认为是一种晶体缺陷，多数研究者认为是受生长螺旋错位、温度波动产生的热应力、不稳定的生长环境等因素影响[4-6]。
2.2 红外吸收光谱分析
选取抛光良好的样品SiC-1/1和SiC-1/2中黄色和绿色部分，弧面型样品SiC-2及公主方型样品SiC-3，对其进行红外光谱测试，结果如图 2所示。结果表明，合成碳硅石样品的红外吸收频率主要集中在880、950、970、1 028 cm-1及1 500 cm-1附近，峰值较为尖锐。其中，880、950 cm-1和1 500 cm-1附近的红外吸收峰由Si-C键对称伸缩振动及反对称伸缩振动引起[7]。据前人研究，815 cm-1附近的红外吸收峰指示样品含有较高的N元素，1 028 cm-1附近的红外吸收峰与晶格振动类型、晶格缺陷以及杂质元素浓度有关[3]。
2.3 拉曼光谱分析
拉曼光谱测试结果(图 3)显示，样品SiC-1在505、787、797 cm-1处均可见拉曼特征峰，且787 cm-1处的特征峰强于797 cm-1处；样品SiC-2在149、766、777、796、965 cm-1处均可见拉曼特征峰，且796 cm-1处的特征峰强于766 cm-1和777 cm-1处；样品SiC-3在172、770、785、796、964 cm-1处均可见拉曼特征峰，且785 cm-1处的特征峰强于770 cm-1和796 cm-1处。964、965、971 cm-1处的拉曼特征峰均归属于单晶硅的拉曼散射峰。对比前人研究结果表明，本文合成碳硅石样品主要为6H型，以149 cm-1和505 cm-1峰位为特征[4, 8]；部分测试结果显示为次多型15R ，以179 cm-1峰位为特征，缺失505 cm-1峰位[3, 9]。样品缺失于1 332 cm-1处的拉曼散射特征峰可与钻石相区分[10]。
2.4 紫外-可见吸收光谱分析
选取不同颜色切片样品SiC-1/1(黄色部分)、SiC-1/2(绿色部分)和SiC-1/3(深绿色部分)以及弧面型样品SiC-2/1进行紫外-可见吸收光谱分析，结果如图 4所示。
综合前人研究认为，样品中410 nm左右的吸收峰为6H-SiC的本征吸收边[11]，440 nm和616 nm两处吸收带是N引入浅施主能级中的电子向导带跃迁所致，从而引起蓝光、黄光的叠加吸收，使样品呈现绿色调，揭示样品掺杂N元素；582 nm左右的吸收带归因于电子从价带向Al受主杂质跃迁，指示样品的掺杂元素为Al[12]。同时，掺杂元素浓度决定了样品的颜色深浅，浓度越高，绿色调越明显，故肉眼观察样品整体呈现为黑绿色[3]。
3. 结论
本文利用激光拉曼光谱仪、傅里叶红外光谱仪及紫外-可见分光光度计等仪器，对绿色合成碳硅石样品进行了常规宝石学及光谱分析，获得以下结论。
(1) 合成碳硅石样品在透射光下观察具有明显色带、典型的白色管状包裹体以及后刻面棱重影，以此区别于钻石。
(2) 红外吸收光谱结果显示，合成碳硅石样品主要为Si-C键振动，同时出现了其它化学键的振动吸收峰，表明其组成成分相对复杂，存在晶格缺陷。
(3) 拉曼光谱结果表明，合成碳硅石样品具多型混合结构，颜色不均匀，以6H-SiC为主，部分为15R-SiC；次多型(15R)区域均对应深绿色部分，推断为杂质元素掺杂浓度过高影响了结构稳定性，最终导致样品呈现6H-15R多型混合结构。
(4) 紫外-可见吸收光谱结果揭示，合成碳硅石中掺杂的杂质主要有N和Al，而主要致色元素为N，且掺杂浓度较高，导致样品呈现较深色调。
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图 2 “唐河玉”样品的微形貌特征
Figure 2. Mico-morphological characteristics of "Tanghe jade" samples
表 1 “唐河玉”透闪石的电子探针分析数据
Table 1 Data of tremolite in "Tanghe jade" samples by EPMA
wB/% 成分 THY-1-1 THY-15-2 THY-23-3 THY-63-1 THY-71-4 THY-103-3 THY-104-1 SiO2 59.067 58.765 59.095 58.066 58.253 59.624 59.236 Al2O3 0.087 0.103 - 0.741 0.253 0.006 0.556 TiO2 0.036 0.007 0.014 0.065 - - 0.012 FeO 0.296 0.123 0.095 0.427 0.293 0.505 0.474 MnO 0.039 0.004 - - - - 0.023 MgO 24.900 24.774 24.705 23.925 24.562 24.933 24.344 CaO 12.491 13.273 13.463 13.343 12.727 13.299 13.504 Na2O 0.035 0.066 0.005 0.052 0.054 0.017 0.082 K2O 0.034 0.014 0.022 0.002 0.004 0.014 0.011 P2O5 - - 0.003 0.016 0.016 0.008 0.017 Cr2O3 0.222 0.253 - 0.080 0.032 - 0.019 CO2 - - - - - - - Total 97.207 97.382 97.402 96.717 96.194 98.406 98.278 Mg/(Mg+Fe2+) 98.83 99.51 99.62 98.25 98.82 98.01 98.09 矿物组成 透闪石 透闪石 透闪石 透闪石 透闪石 透闪石 透闪石 注：“-”表示该成分低于检测限 
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