GRS警报：一种新型合成尖晶石在曼谷珠宝展上出现

前言（本部分为个人总结）
本文发于2015年9月14日，由于近期都没有关注GRS所以我也是最近才知道，有兴趣可以去参考官网。GRS Alert: A new type of synthetic spinel appears at the Bangkok show
文章中一些具体的专有名词和技术，方法等本人不是很清楚具体情况，可能有一些翻译的不对，如果有误请指正。
本文中很关键的“flux pulled method”我不太清楚是指电磁拉伸还是液态拉伸，基于液态焰熔法翻译为液态拉伸法。（我想这部分对于消费者来说具体操作并不重要，也许有不严谨的地方，需要更严谨的更详细的资料请自己去查）。
另外很多普通消费者可能不清楚为什么关于宝石研究最新最高精尖的讯息为什么不是在欧美等技术强国出现反而出现在东南亚小国泰国。那我告诉你泰国是世界上最大的宝石交易地，泰国人也最热衷于研究各类宝石加工处理合成方法，从早期的红蓝宝石的优化处理，到最近的红宝碧玺辐射处理，帕拉依巴加热处理，再到现在最新的合成尖晶石，基本都最早或者最集中在泰国，也最早在泰国市场上出现，宝石界大神几乎都蹲守在泰国研究，因为在泰国是一手资讯，等到欧美消息都不知道转了几手是多少年以后的事了。
虽然泰国人热衷“研发”，但是他们并不藏着掖着，这是我很喜欢泰国人的一点，比如文中这家研发的公司，很明显非常配合GRS的研究并且提供样本。对于泰国人来说，宝石的优化处理在他们看来更像是一种科技，一种研究成果，他们非常自豪展示这种成果，毕竟这个世界上也有需要这些合成宝石的人。在他们看来这并不是一种造假，因为他们会很明确的告诉你这是那一类处理的宝石，但是一些转手的人，比如印巴人，东南亚一些旅游区的人，或者一些我也不想说是哪里的人，利欲熏心，在转卖过程中刻意隐瞒，当然也不排除有些人什么都不懂，跟ta说半天还是傻愣愣的什么都记不住，或者语言水平也不行，解释半天ta只拣着自己想听的听了，其他一概略过。等东窗事发的时候全部装无辜一股脑把责任全推到泰国人头上，让泰国人背锅。
当然我不是说泰国人都没有骗子，好人坏人哪里都有这点大家要理智看待，泰国用假宝石骗人的人也不少，不过相对来说越是源头，这水就越干净点，这就是为什么我只找泰国的源头供应商买货，因为他们一般都很诚信，尤其只会和合作久的人买货，还有为什么我更相信泰国专业鉴定机构的证书，因为他们在宝石方面的资料是最新最全面的。
以下是本文正文
只翻译了一些对大家有用的讯息，剩下一些研究数据之类的，我想对消费者意义不大，有兴趣自己翻译，贴出原文。
介绍
 2015年5月，笔者（AP）了解到，泰国一个公司（Tairus有限公司，曼谷）向俄罗斯一个实验室定制了用液态拉伸晶体方式制作的新型的人工合成的“薰衣草”色尖晶石。同样的技术曾在西伯利亚一个单晶体研究所使用。 笔者（AP）之前在此西伯利亚的研究所考察过。 通过这次访问，AP制作了一个关于在西伯利亚使用的这种方法的教学视频，图318a-b显示的是两个截屏。液态拉伸制作尖晶石也被叫作Czochralski法，这种方法可以被修改用于产生化学合成尖晶石。(Grabmaier et al., 1968 and Wyon et al., 1986).
 通过确认这种新型合成尖晶石在俄罗斯首都莫斯科郊外的一个私人实验室生产而非西伯利亚，然而使用的是同样的设备。GRS获悉，已经有这一系列尖晶石在宝石鉴定实验室被鉴定为“天然尖晶石”。. 一些宝石鉴定的副本强调了这一点。我们没有验证这一说法的真实性，但是已经通知了相关实验室，在此匿名。
这种在交易过程中早期出现的可能错误鉴定的迹象让我们确信这种材料会对宝石业形成威胁所以必须向宝石业发出预警。
                
                
图318a-b:在西伯利亚单晶体研究所的液态合成生产设备。
图318b:通过观察窗口看到固体的物质被液态拉伸。 Photos taken in 1994 by AP.
                
                
图319： 管内在合成尖晶石中加入了紫色。这根管中表面产生的螺钉状印记表明了尖晶石正在被旋转液态合成。
原料，颜色种类和内含物
在曼谷的Tairus办公室参观期间，新产品正摊放在桌子上，在市场上试运行后需求大量增加。（图320） 一系列不同的产品用带数字的标签区分开来以便进行切割和区分不同颜色种类。 在粉红到蓝之间包括了所以种类的大概11个颜色正在被生产。不同的色调包括非常经典的充满活力的粉红色（所谓绝地武士），红色等，模仿遍了世界上所有最贵的尖晶石品种，包括转变为几乎纯“荧光”蓝色（钴尖晶石）。浅紫罗兰色和浅紫色或者“薰衣草”色（图322a-d），以及在白炽灯下会变为粉色的变色紫罗兰色尖晶石（图323）也有供货。其实助熔法生产的粉-红和蓝色合成尖晶石在20年前就在市场上被知晓，液态拉伸的“薰衣草”色和变色品种是新加入的。这些颜色迄今只被火焰融合产生。GRS要求切了一些不同的产品，包括曾被排除的包含内含物的样品以及一些更大的原石。（见图321a-b）
                
                
图320：市面上液态拉伸法制造的尖晶石。被标注直径近5cm的圆柱体和不同颜色种类 。这个原石的尺寸差不多250ct.。 Photo by AP at Tairus, Bangkok.
                
                
图321a-b:合成的尖晶石的粗糙的条纹细节表明在他们被液态合成当中曾被拉伸，垂直于条纹的环也表面他们曾被转动。
                
                
图321b
四块在GRS位于曼谷的切割设备切割的尖晶石几乎包含了所有免费样品，完美的模仿了越南尖晶石(Fig. 322a-d)一些被排除的样品在表面有有趣的过度生长现象和内含物特征。(图327-328)这些内含物包括各种针尖状气泡(Fig. 327)，不透明的立方固体群(Fig. 340a)，以及圆形的晶体 (Fig. 335-337)。大的弯管在原石中被发现但是未必会出现在切割后的宝石中(Fig. 328b-c).。
这些管状中有一种类似于螺钉(Fig. 319)可以被看作这个尖晶石肯定被液态旋转过的指标。这种拉伸方式在原圆柱状的原石表面发现的条纹状证实，这种条纹在圆柱体的长轴方向。(Fig. 321a-b)
                
                
图322a-d:不同颜色的液态拉伸法制成的尖晶石，包括粉-红，薰衣草，变色和蓝紫色颜色种类。由GRS切割的合成尖晶石，每一个均超过1克拉。
                
                
图323
由液态拉伸法制成的变色合成尖晶石，由紫罗兰色（日光）变色至紫粉色（白炽灯），接近一克拉，GRS由原石切割而成。
                
                
图324
合成尖晶石圆柱体的显微照片显示出粉色和紫罗兰色的带状颜色扩散区。
                
                
图325
通过交叉偏振器的偏光镜看两个合成尖晶石。左边是一个VERNEUIL合成尖晶石，右边是新型的液态拉伸尖晶石。注意到只有Verneuil尖晶石显示交叉线异常干涉图案。
以下为一些数据和检测，需要的自己看。
Color zoning and UV-fluorescence
With fiber optic illumination, diffuse cloudy color zoning was visible in some samples (Fig. 324). All samples showed a strong red UV fluorescence at shortwave (254nm) and longwave (366nm) UV excitation. Corresponding color varieties of natural spinel from Vietnam, Burma and Tanzania did not show this fluorescence under UV light. This is a good screening test for natural parcels of fancy colored spinels.
Standard gemological tests
The new synthetic spinels have RI’s ranging from 1.714 – 1.715. These are typical RI’s for natural or synthetic flux spinels but different than RI’s found in Verneuil spinel (RI 1.725-1.730). Also the density is within the range of natural and flux spinel (? = 3.5). No anomaly in birefringence was observed (see comparison to Verneuil spinel Fig. 325). These synthetic spinels under crossed polarizing filters, they remained dark (isotropic). The absence of anomalous birefringence is often considered a critical test to distinguish natural spinel from their synthetic counterparts produced by the Verneuil process. It has to be remembered though that synthetic spinels produced by flux methods are indistinguishable by only using the polariscope as testing tool (lit. 3 & lit. 4).
                
                
Fig. 325: Two synthetic spinels as seen trough a polariscope with crossed polarizers. Left a Verneuil synthetic spinel and on the right the new type of synthetic spinel produced from flux. Note only the Verneuil spinel shows cross-hatched anomalous interference patterns.
                
                
Fig.328a
                
                
Fig.328b
                
                
Fig. 328a-c: These types of irregular tubes with 2-phase inclusions (solid and gas phases) are occasionally found in these pulled synthetic spinels. They may only be found in rejected rough materials and it may well be that they are not present in the faceted stones that appear on the market.
Advanced investigations
In order to characterize this material with advanced methods, we have studied the samples by ED-XRF (Fischerscope XUV773, with vacuum, quantitative) and LIBS-analysis (Laser induced breakdown spectroscopy at 30 mJ frequency, 266nm Nd:YAG laser (Continuum, USA) with a pulse width of 6 ns, coupled to an in-house built ICCD/Echelle spectrometer with a working range of 190-900nm, qualitative) for chemical composition, by SEM-EDX (FEI XL30 Sirion FEG, EDAX) for inclusion analysis, by photoluminescence (custom-built, PL405nm and PL535nm, using a Avantes quadruple-channel Czerny-Turner spectrometer) and by UV-VIS-NIR spectroscopy (custom-built, UV-VIS-NIR using a Avantes quadruple-channel Czerny-Turner spectrometer and two broadband light sources) for the analysis of the color origin.
Results
Absorption spectroscopy
The UV-VIS results revealed classic spectra of Cr- and Co-bearing spinels (Fig. 329) lacking Fe concentrations.
                
                
Fig. 329: UV-VIS-NIR absorption spectra recorded at liquid nitrogen temperature (LNT) for the respective groups: Russian synthetic spinel (pulled from flux) of different colors (pastel pink, purple, violet and blue) from Russia. Important features are highlighted. The ordinate shows the absorbance in arbitrary units. Note the typical absorption characteristics of Co in spinel structure in the range 550nm to 650nm, superimposed to those of Cr. Increase in Co concentration for pink to blue colors. Measured with GRS UV-VIS-NIR analysis system using Avantes AvaSpec with a quadruple-channel Czerny-Turner spectrometer.
 
Chemical composition
ED-XRF analysis confirmed that the chemical composition contains typical stoichiometric Mg and Al concentrations found in natural and synthetic flux spinel (Tab. 9). The Co concentrations of these synthetic spinels are in the same order of magnitude as other natural spinels of same color but higher in Cr and lower in Fe and Zn.
Surface spot analyses by ED-XRF focusing on opaque particles revealed the presence of platinum (Pt), iridium (Ir) and bismuth (Bi) (Fig. 330-331). The analyses by SEM-EDX confirmed the presence of Ir particles and in addition xenomorphic Mg-Al-Si-solids that were detected on the surface of the spinels. During LIBS-analyses we focused on the presence of Li and Be concentrations in these new spinels. Natural and synthetic spinels have similar concentrations of Li. Be is detected in all the natural spinels tested. None of the synthetic spinels tested showed any detectable quantities of Be, except on the unpolished rim of the boule.
Interpretation
The blackish solid clusters seen in the microscope could be identified as predominantly Ir particles, which are coming from the crucible (Lit.1). Only one Pt particle could be detected (by ED-XRF spot analysis) whereas all the other particles were identified during SEM-EDX as Ir particles (size see Fig. 339-340). The presence of Si in the chemical analyses (Tab. 9) can be explained by the presence of silicate particles that were found during SEM-EDX analyses (Fig. 338) and are not part of the chemical composition of these synthetic spinels. Bi concentrations are localized by ED-XRF in the area of the filled tubes and are most likely part of the flux used. Ir and Pt may be part of the crucible or corrosive products of other parts used in the production process. The role of Si in the process and the nature of these Si-bearing solids are not yet understood. The light element test by LIBS for distinction of natural and synthetic spinels (e.g. presence of Be in natural spinels only versus no Be in synthetic spinels except on unpolished surfaces of the outer rim of the boule), can also be applied to identify this new synthetic type of spinel (Lit. 1).
                
                
Tab.9: ED-XRF analyses of selected synthetic and natural spinels of corresponding colors. Note the presence of higher Cr and absence of Fe in the synthetic spinels. Natural spinels are characterized by higher Fe, Zn, V, Ti and Ga concentrations. Si concentrations in synthetic spinels are due to inclusions (see text).
                
                
Fig. 330: ED-XRF analyses of an area in the synthetic spinel with presence of tubes revealed concentrations of Bi (Pt and Ir is due to black particles present as overgrowth on the surface and as inclusions). A microphotograph of the tubes is shown.
                
                
Fig. 331: ED-XRF analyses of the surface of the new synthetic spinel in an area of 2 different type of opaque particles (inserted picture in reflected light). The analyses revealed Pt and Ir concentrations.
 
Photoluminescence
During PL analysis we found that the new material produced prominent emission spectra when analyzed with 2 different lasers at room temperature as well as at low temperature using liquid nitrogen (Fig. 332). The peaks around 680 to 730 nm are due to the Cr concentrations in these synthetic spinels and the position of Cr in the crystallographic lattice. These spectra have not been observed in other synthetic spinels produced by flux or Verneuil and are also different than those found in heated spinels (Fig. 303-304) and all other natural spinels tested so far in this book. However, they are similar to the PL of cobalt diffused natural spinels that we reported earlier (Fig. 310).
Interpretation Photoluminescence
The PL-results seem to indicate that this new type of synthetic spinel is produced by a new process so far unknown to the gemological world. They have characteristics of “normal spinel” with some slight Mg-Al disorder. Mg-Al ordering is strongly influenced by the rate of quenching (Widmer et al. 2014). Therefore, a multi-step process in the production of these new spinels (pulled from flux and tempered) can also not be excluded.
                
                
Fig. 332 PL: spectra (excitation 405nm) of synthetic spinel recorded at liquid nitrogen temperature (LNT) for the respective groups: Synthetic spinel (pulled from flux) of different colors from Russia. The ordinate shows the intensity (counts) in arbitrary units. Note the PL lines and their position are found in either normal or inverse spinel. The synthetic spinel is interpreted as normal spinel with slight Mg-Al disorder. Measured with GRS’ photoluminescence analysis system using Avantes AvaSpec with a quadruple-channel Czerny-Turner spectrometer.
Fig. 333 PL spectra (excitation 532nm) of synthetic spinel recorded at liquid nitrogen temperature (LNT) for the respective groups (see Fig. 333)
                
                
Fig.334a
                
                
Fig. 334a-b: SEM-BSE image of synthetic spinel with a rough surface and surrounding overgrowing particles. Note that the series of small Ir particles are found as clusters as well as in a circle bordering an isolated round spinel area. SEM-EDX spectrum of Ir particles measured at 20kV acceleration voltage is inserted (Fig. 334b).
 
                
                
Fig. 335: Pear-shaped round inclusion in synthetic spinel was identified as spinel.
 
 
                
                
Fig. 336: Round spinel inclusion inside the synthetic spinel reaches the surface of the rough and is bordered by a rim consisting of Ir (see Fig. 334b).
 
 
                
                
Fig. 331: A bicolored area of the rough reveals an isolated round spinel material that it is not an inclusion of a different material. It may be misinterpreted as an inclusion supporting natural origin of the synthetic material.
 
 
                
                
Fig.338a
 
 
                
                
Fig.338b
 
 
                
                
Fig. 338a-c SEM-SE image of the surface of the synthetic rough material allowed to analyse overgrowing substances. It is seen that the surface contains swirled solid substances filling cavities of the rough surface. EDX spectra of the material confirms that the particles are composed of Mg-silicates and Mg-Al-silicates (see inserted spectra).
 
Conclusion
A new synthetic spinel appeared on the market that is produced by the crystal pulling method from flux. Standard gemological tests are not conclusive (RI in the range of natural counterparts). A first indication for synthetic origin is the intense red UV fluorescence that is stronger than in the color varieties of natural counterparts. This is due to the high Cr concentrations in this synthetic cobalt-spinel and the absence of Fe concentrations. Typical inclusions are often absent in these new spinels. If they are present, they include opaque clusters of solids (Ir particles from the crucible), curved tubes filled with flux (containing Bi) as well as myriad pinpoints. A diffuse color zoning may be observed as well. The new synthetic materials can be distinguished by ED-XRF analyses by their absence or lower concentrations of Zn, Fe and Ga. Higher Si concentrations are due to Mg-Al-Si solid inclusions. Bi concentrations are located in areas with Flux inclusions; Ir and Pt is due to opaque inclusions. PL analyses identifies these spinels as “normal” with slight Mg, Al disorder. The light element test is of limited use due to Lithium concentrations in the stone and Beryllium concentrations on the surface. These new synthetic spinels may appear in the market as imitations mixed into lots of lavender to pastel blue spinel originating from Vietnam or other origins.
 
                
                
Fig. 339a-f: image of the surface of the new synthetic spinel produced by flux (pulled method). Numerous particles composed of Ir were identified in the shape of triangles (Fig. 339c) or hexagons (Fig. 339a and e). The particles may also form clusters (Fig. 339b) and can be misinterpreted as opaque inclusions suggesting natural origin. All particles were identified by SEM-EDX as Ir alloy.
 
 
                
                
Fig. 340a: Microphotograph of clusters of solid black inclusions occasionally present in the new synthetic spinels. Attention: May be misinterpreted as a natural phenomenon.
 
 
                
                
Fig.340b
 
 
                
                
Fig. 340b SEM-BSE image details of particles found on the surface of the new synthetic spinels. They are composed of Ir. A round inclusion turned out to be of Ir particle as well (see inserted SEM-EDX spectrum).
 
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Literature
1. D’Ippolito, V., Andreozzi, G.B., Halenius, U., Skogby, H., Lamenter, K., and Günther, D. (2015) Color mechanisms in spinels: cobalt and iron interplay for the blue color. Phys. Chem. Minerals, 42, 431-439.
2. Grabmaier J.G., Watson B.C. (1968), Czochralski Growth of Magnesium-Aluminum Spinel, J. Am. Ceram. Soc. 51(6), p. 355-356.
3. Muhlmeister, S., Koivula, J. I., Kammerling, R. C., Smith, C. P., Fritsch, E., and Shigley, J. E. (1993) Flux-grown synthetic red and blue spinels from Russia. Gems & Gemology vol.29 n.2, 81-98.
4. Pragati Verma (WINTER 2014), Unusual Short-Wave UV Reaction in Synthetic Blue Spinel GEMS & GEMOLOGY VOL. 50, NO. 4, 312
5. Wyon C., Aubert J.J., Auzel F. (1986), Czochralski growth and optical properties of magnesium-aluminium spinel doped with nickel, J. Crystal Growth; 79(1-3-79), p.710-713.
6. Widmer R., Malsy A.K., Armbruster T. (2015) Effects of heat treatment on red gemstone spinel: single-crystal X-ray, Raman, and photoluminescence study. Phys. Chem. Minerals 42, p.251-260