Fluorescence Characteristics and Main Fluorescence Component in Burmese 'chameleon' Amber.

One special variety of Burmese amber is "chameleon" amber, named for the bluish-green colour that appears to float on its surface. This material is found in the famous Tengchong market in Yunnan Province, China's largest Burmese amber market. Its bodycolour ranges from golden brown to brownish-red or even red. When exposed to sunlight or strong white light against a black background, its surface shows a uniform green colour. This research presents the gemological properties, spectral characteristics and organic components of Burmese 'chameleon' amber. Three-dimensional (3D) fluorescence spectra showed that Burmese 'chameleon' amber had fluorescence centres near 433, 465 and 470 nm, and the excitation wavelengths of the fluorescence centres of Burmese 'chameleon' amber were shifted from the ultraviolet region (380 ± 10 nm) to the visible region (410 ± 10 nm), with the emission wavelengths concentrated at the bluish-green region. Through the colour simulation and superimposition, the phenomenon of floating bluish-green fluorescence colour of Burmese 'chameleon' amber is not only derived from bluish-green fluorescence centres, but also enhanced by the mixture of surface fluorescence and its bodycolour. Headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis demonstrated the variety of aromatic compounds in Burmese 'chameleon' amber was related to geological process and the presence of fluorescence components. The high-performance liquid chromatography-fluorescence detector obtained some fluorescent aromatics, particularly benzo[a]anthracene with yellowish-green fluorescence, which is responsible for the fluorescence characteristics of Burmese 'chameleon' amber.

Evaluation of natural ageing responses on Burmese amber durability by FTIR spectroscopy with PLSR and ANN models.

Amber ageing is an inevitable process, which is very important in precious organic gemstone relics protection. In order to explore the mechanism of amber ageing and estimate the durability of Burmese amber, this research investigates the changing spectral features of Burmese ageing amber via Fourier Transform Infrared Spectroscopy (FTIR) and solid 13C Nuclear Magnetic Resonance spectroscopy (NMR) and develops the regression models for its micro-hardness by micro-FTIR spectra. The Partial Least Squares Regression (PLSR) and Artificial Neural Networks (ANN) methods as well as Competitive Adaptive Reweighted Sampling (CARS) algorithm for wavelength variables selection have been applied to predict and assess the Vickers hardness of amber samples with different ageing degrees. As a result, the FTIR and the solid 13C NMR spectra reveal that the contents of CO groups (of esters) increase substantially, and which of the other oxygenic groups (CO (of acids), COC, COCC) increase modestly in amber ageing. When comparing with the results of four different models (PLSR, ANN, CARS-PLSR and CARS-ANN), the CARS-PLSR model obtained the optimal results as follows: the squared correlation coefficient of calibration(R2cal) is 0.9230 and the root mean square error of calibration (RMSEC) is 1.2977 HV; the squared correlation coefficient of prediction (R2pre) is 0.7762 and the root mean square error of prediction (RMSEP) is 2.2208 HV. The overall results sufficiently demonstrate that FTIR spectroscopy technique coupled with appropriate chemometrics methods are very promising tools to estimate and predict the hardness property of Burmese ageing amber.

[Infrared Spectral Characteristics of Ambers from Three Main Sources (Baltic, Dominica and Myanmar)].

Infrared spectra of ambers from Baltic, Dominica and Myanmar are obtained by Specular Reflection and KBr Pellet Transmission Methods. Although the infrared spectra of these ambers present similar features for ambers from different locations, refined differences in location and intensity of absorption peaks could be identified among them. Between 3000 and 2800 cm(-1), two obvious bands with a weak shoulder peak are seen in the Baltic amber spectrum, whereas there are two bands in the Dominica's and three bands in the Myanmar's. In region of 1740~1690 cm(-1), one band appears at 1732 cm(-1) in the spectra of the Baltic amber sample, distinctly different from those of the Dominican and Myanmar ambers which have a doublet at 1730 and 1695 cm(-1). For the Dominican amber, the intensity of 1730 cm(-1) is much stronger than that of 1695 cm(-1), being contrary to the spectra of the Myanmar amber, whose intensity of 1730 cm(-1) is weaker than that of 1695 cm(-1). Within region of 1300~1000 cm(-1), Baltic amber can be distinguished from other two origin ambers by a horizontal shoulder, often called "Baltic shoulder", with a definite band at 1163 cm(-1). Spectra of the Dominican amber show a unique band at 1240 cm(-1), while spectra of the Myanmar amber have a triplet at 1224, 1130 or 1154 cm(-1) and 1033 cm(-1), like "wave of mountain" altogether. Ratios of absorption intensity of 1381 vs. 1456 cm(-1) are about 0.9, 0.8 and 0.7 respectively for the Baltic, Dominican and Myanmar ambers. These differences of absorption spectra could be used as the identifiable characteristics corresponding to the ambers locality. The correlation between the ambers' infrared spectra and localities is probably due to their age, plant provenance and geological environment indivadually. On the basis of presence and intensity of the bands attributed to exocyclic methylene groups, it is suggested that the Myanmar amber formed earliest, followed by Baltic and then the youngest Dominican. These finding reveals that infrared spectroscopy may have significance for identifing amber locality, and thus potentially have archeological implications in determining source of some ancient ambers.

[Mineralogical and spectral characteristics of "Gaozhou stone" from Jiangxi Province].

The seal stone is a kind of artwork with historical and cultural characteristics of China, which has been playing an important role in Chinese traditional culture. "Gaozhou stone", a new kind of the seal stone, has been found in the market recently. To investigate the mineralogical and spectral characterastics of "Gaozhou stone", samples were studied by using XRF, XRD, FTIR, SEM and DTA. Measurements by XRD reveal that kaolin minerals (kaolinite, dickite), pyrophyllite and minor sericite and illite occur in the ores. When kaolinite and dickite are associated, it is not easy to differentiate them from each other. Although some reflections overlap others, kaolin polytypes can be differentiated by XRD patterns in the range 18°-40° (2θ), the reflections at 0. 395, 0. 379, 0. 343, 0. 326, 0. 294, 0. 280, 0. 232 and 0. 221 nm are diagnostic of dickite. The XRD results indicate the presence of transitional mineral of kaolinite and dickite in these samples. The main chemical components of "Gaozhou stone" are SiO2 and Al2O3 with minor Fe2O3, K2O and Na2O, corresponding with that of kaolin minerals. The OH groups in kaolin group minerals have attracted considerable attention as a sensitive indicator of structural disorder. In principle, dickite has three bands, whereas kaolinite has four bands at the OH-stretching region. According to the results of FTIR, transitional mineral of kaolinite and dickite in "Gaozhou stone" has 3 absorption bands of 3 670, 3 650 and 3 620 cm-1 in high frequency region. The intensity of 3 670 cm-1 band that belongs to outer layer hydroxyl vibration is approximately equal to the intensity of 3 620 cm band ascribing to inner layer OH vibration. This value will only have subtle changes due to the different component ratio of kaolinite and dickite layers. Micro-morphology viewed by SEM presents irregular platy or pseudo-hexagonal platy particles with an average diameter of 0. 5-4 µm of "Gaozhou stone". Such morphologies are quite similar to other seal stones of China that the formation environments of all these stones are of the same kind. DTA curves demonstrate that the disparity of dehydroxylation temperature can be seen as a differential feature for identifying kaolin group minerals, but that is not undoubted. And what's more, the size of the mineral grains seems has a greater effect on the disparity of dehydroxylation temperature. This research shows that the mineral type of "Gaozhou stone" is similar to "Four Famous stones of China", and it could be a viable substitute of other famous seal stones. In this point, "Gaozhou stone" has a broad market prospect.

[Source Constraints on Turquoise of the Erlitou Site by Infrared Spectra].

Shiyan district in Hubei province is a famous locality of high-quality turquoise with brightcolor, finegrain in the world. Erlitou archacologicalsite, which is about 300km north to the Shiyan Turquoise mine, has been excavated a remarkable number of turquoise artifacts since 2002. Some researchers infer that there was "a road of turquoise" between the two sites in history. In order to check the inference, and identify local features of the turquoises found in Shiyan, and Eelitou site as well, spectra of three turquoise groups from Shiyan, Hubei and one group of Erlitou unearthed samples were obtained by means of IR. Their spectra have visible differences in the 1 200-950 and 700-400 cm(-1) range. Peak 1 174 cm(-1) appears only in samples from Wenfeng, and from 700 to 400 cm(-1), 5 peaks show in samples from Wenfeng while 7 peaks emerge from the other two sites. Turquoises in Erlitou site have similar spectra to those from Qingu and Yungaisi, and are more similar to Yungaisi of peak around 1 159 cm(-1). According to A = lg(1/T) , intensity of transmittance spectra were calculated and then Ratios(A783 cm(-1)/A837 cm(-1)) were yielded. The ratios of samples from Qingu, Wenfeng, Yungaisi and Erlitou site are 0.819-0.920, 0.870-1.010, 0.806-0.860 and 0.827-0.878 respectively, allowing for a suggestion that turquoise in Erlitou site was the most probable from Yungaisi. This research can be used as example for identifying origin of the unearthed turquoise relics, which is more likely a good tool for archeological research.

[Vibrational spectra of black species of hetian nephrite (tremolite jade) and its color genesis].

Black nephrite is a very uncommon jade type currently found only at Karakashi. In order to study the spectral characteristics and color-genetic mechanism of the black nephrite, samples collected from Karakashi were studied using EMPA, IR, Raman and XRD. The results are as follows: nephrite with different color has nearly the same major chemical compostions, while the black ones contain higher carbon; nephrite with different color has similar vibration spectrum, while the black ones show characteristic peak of graphite. It is speculated that the color of black nephrite is not only related with actinolite, but also related with the graphite inclusions. Obviously, Raman spectra is a very important nondestructive method to identify the color genesis and the origin of the black nephrite.