琥珀的宝石学研究综述

A Review for the Gemmological Research on Amber

琥珀是由不同地质时期古植物分泌树脂化石,属典型的多组分有机大分子聚合物,是集多种学科交叉研究于一身的天然有机宝石。琥珀的形成与演化因其内部成分和结构发生改变而逐渐“成熟”,而其外部受古气候、古地理、古植物、沉积环境等因素综合控制,致使不同产地琥珀的宝石学性质、谱学特征、化学成分、显微结构、评价要素、市场价值等迥然不同,对其进行深入而详细地研究具有重要的科学意义及应用价值。笔者携研究团队本着由表及里、由简入繁的研究思路,基于琥珀的红外光谱、光致发光光谱和稳定同位素示踪技术等方面构建了多视角、多维度的琥珀产地溯源数据库;琥珀的发光行为(荧光和磷光)是其重要的宝石学性质,不同地质时代形成的琥珀因包含不同的发光物质而呈现独特的发光现象,采用JASCO FP8500三维荧光光谱仪和FLS980时间分辨荧光光谱仪测试了不同产地琥珀激发光谱、发射光谱、相对强度及发射波长的衰减时间(即寿命),对琥珀总的发光行为进行了量化表征,并依据荧光参数提出了琥珀的评价要素和品质评价体系。琥珀的优化处理技术随着市场的需求不断更新换代,及时跟踪琥珀优化处理新产品,解析优化处理机制,寻找鉴定特征,已成为鉴别琥珀的长效技能。琥珀主体成分的解析难度极大,通过气相色谱-质谱(GC-MS)联用技术得到饱和烃、芳香烃、非烃馏分组分和不溶高聚物四个大类,继而在多米尼加琥珀的可溶化学组分中采用高分辨质谱、核磁共振等技术,首次提出15-nor-cleroda-3,12-diene[15-降-克罗-(3,12)二烯]是多米尼加琥珀的特征生物标志物,即二环二萜的二烯类克罗烷是多米尼加琥珀的基本骨架类型,确定了其平面和立体结构,拓展了传统认知中半日花烷是琥珀唯一原始骨架单元结构的学说。琥珀作为珍贵的文物遗存,通过科技考古溯源文物的来源,可以揭示琥珀所记载的东西方文化交流的信息。

Amber,an organic gemstone also named fossil resin,gradually matured from the liquid resin secreted by paleobotanical trees in different geological ages.During the long fossilization process,the internal components and chemical structures in the initial liquid resin were maturated into these of fossil resins,which integratedly controlled by many external factors,like paleoclimate,paleogography conditions,mother-trees,and depositional environment.These inconstant factors lead to that amber from different producing areas enormously varies in the gemmological characteristics,spectral features,chemical components,micro-structures,quality evaluation indices,and market values.Thus,it is of great scientific significance and application value to study amber deeply,systematically,and in detail.Based on the research approach of from the surface to the inside,from the simple to complex,the authors and the research team established a comprehensive database for amber.This database includes the mid-infrared spectra collected by KBr pellets pressing method,the excited-emission matrix by JASCO FP8500 fluorescence spectrometer,the time-resolved phosphorescent spectra and the decay times by Edinburgh FLS980 spectrometer,as well as the stable isotope tracing technology.Current application of this database is used in the geographic identification of amber and ancient amber artworks.Meanwhile,the luminescence behaviors(fluorescence and phosphorescence),as the important gemmological properties of amber,have been deeply studied,and the potential fluorescent components have been analyzed.A quantification of the total luminescence behaviors’parameters in amber laid the foundation to propose blue amber quality evaluation indices and rules.On the other hand,the amber enhancement and treatment technologies are developing rapidly to meet the market kinds of new demands.Focus on characterizing the gemmological and spectral features of various new-type man-made amber products in market,a series of identifying methods are proposed and keep updating with the market demands refresh.Additionally,amber as a natural macromolecular polymer,because of its complex multi-components,it has become one kind of significant objects in various interdisciplinary studies.Amber contains lots of volatile and non-volatile components,varying with its producing areas.Due to its slightly solubility in normal organic solvent,the compounds dominant in amber are extremely hard to isolate and purify.The biomarker named 15-nor-cleroda-3,12-diene was firstly identified from a Dominican amber sample,by gas chromatography-mass spectrometer(GC-MS)detection for the saturated hydrocarbon,aromatic hydrocarbon,non-hydrocarbon fractions composition and insoluble polymers.Then combined with the high resolution mass spectrometer and nuclear magnetic resonance(NMR)technology,its planar and stereoscopic structures were determined.This proposal indicates that Dominican amber is not only based on polymerized labdanoid diterpenes,but also on 15-nor-cleroda-3,12-diene which has typical the cleroda-diene skeleton structure.Amber as a precious cultural relic,current scientific and technological archaeology provides a new sight to trace the amber relics ancient producing areas,and further reveals the ancient communication between East and West cultures.