Tourmaline PARAIBA "Refining and imitations"

The most common refining method for Paraiba tourmalines is heat treatment. It is produced with the aim of giving the stones a blue-green or blue color. Also, among the types of refinement, there is often the impregnation of open cracks and cavities in tourmalines with various compositions that improve the external perception of the quality of the stone. Adhesives are often used to prevent the destruction of low-quality stone during processing (cutting, cabochon, stone cutting). There are frequent cases of staining pale colored stones along cracks with colored filler. Techniques for diffusion staining of tourmaline are described in the literature, but there is no information on the commercial distribution of such a technique. In connection with the high prices for "paraiba", prevailing in the world market, very often you can find stones imitating tourmaline in color characteristics. The most common and easily recognizable imitations are zircon, apatite, cubic zirconia and even glass. Copper-bearing elbaites, which do not have an admixture of manganese, or even ordinary indigolites, are often given as "paraiba". Recently, they often try to sell hemimorphite under the guise of “paraiba”, which has nothing to do with the tourmaline supergroup. As a rule, hemimorphite has low purity characteristics and specific faceting, which makes it difficult to determine the optical character of the stone (axiality) and refractive index on a refractometer. Either bevelled stones with multiple polishing defects on the edges are used, or cabochon cut, which does not allow accurate reading of the refractive index values. For loose stones, an uncomplicated and reliable method of determination is to measure the specific gravity of the stone, since the differences between paraiba tourmaline and hemimorphite in this indicator are very significant. For fixed stones, the diagnostic method that gives the most accurate results is Raman spectroscopy, which allows you to quickly and accurately determine the mineral belonging of the stone.