[The Gemological Characteristics of One Kind Turquoise Imitation]

It has been a long time that the imitations of turquoise appear in gem market. Pressed dyed carbonate in the early stage and dyed variscite, chalcedony as well as magnesite appeared in succession. These kinds of materials do not have the color and characteristics of natural turquoise. Their physical and optical properties are quite different from natural turquoise. One kind of turquoise imitation newly appears in market is selected to be studied in this paper. The conventional gemological method, infrared absorption spectroscopy and X-ray diffraction were employed to study its mineral compositions, gemological properties and structural characteristics. The results show that: the brecciated structure can be observed and the distribution of the iron wire is very simple on the surface of the sample. Deep blue granules are visible on the surface of blue samples and a few black spots can be observed on the surface of white ones, which are typical indication of pressing process. The blue imitations of turquoise has been stained and pressed. The index of this kind of turquoise imitation range from 1.54 to 1.58, which is lower than that of natural turquoise and it show bluish white fluorescence, which can be used as important evidence to distinguish it with natural turquoise. The data of X-ray diffraction shows the sample mainly consists of enstatite and quartz. The results of infrared absorption spectroscopy show that the absorption spectra of this kind of turquoise imitation is in accordance with the typical absorption peaks of enstatite: the absorption peaks which locates near 1 088 and 799 cm-1 are associated with Si—O, Si—O—Si stretching vibration in quartz; the absorption peaks near 2 947 and 2 882 cm-1 is related with stretching vibration of CH2 of exotic organic resin; the absorption peaks near 1 736 and 1 510 cm-1 are resulted from the bending and stretching vibration of CO and CH2.