Gemmological and Mineralogical Characteristics of Jade Called“Dumortierite”from Jewellery Market

As a new kind of jade“dumortierite”，a blue mineral appears in the jewelry market recently.In order to study its gemmological and mineralogical characteristics，the authors selected 4 samples to test.By using infrared spectrometer，Raman spectrometer，X-ray powder diffraction，USB 4000 fiber optic spectrometer and polarizing microscope，some conclusions can be drawn.The samples are polycrystalline aggregation mainly consisting of quartz and dumortierite，and the content of quartz is quite high，mainly 55%.Most of the quartz is cryptocrystalline texture under polarizing microscope，and some quartz can be seen by naked eyes.The content of dumortierite is about 35%，and the single dumortierite crystal is very little.The quartz and dumortierite appear to be mosaic structure，and the pleochroism of the single dumortierite crystal can be observed in plane-polarized light，and interference colour is orange-yellow and blue-green.A lot of dumortierite crystals exist as inclusions of quartz，needle-shaped or columnar-shaped，and the crystal form is complete.Some dumortierite crystals exists in polycrystalline aggregation, Except for quartz and dumortierite, some cement and auxiliary minerals can be found in the sample, whose content is about 10% Raman spectrum shows the auxiliary mineral is rutile. UV-Vis spectrum of the sample displays absorption peak at 437 nm, which reveals it is concerned with Fe. Fe leads to the blue colour of dumortierite and finally results in the colour of sample.