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The tourmaline is a kind of silicic acid rock mineral. As its Chinese craft name Bixi, which means valuable gem, the tourmaline is ranked among the middle level gems. The crystal structure and formation of the tourmaline: trigonal system, compound single pyramid trigonal system, prism crystal; the two ends have different crystal surface. Usually, There are vertical lines on the surface of the prism, and the transect is spherical triangle. The shape of the aggregate is like stick, emanant, or bundle of needles, and sometimes it is dense massive or hidden crystal massive.
Generally the tourmaline is contained in the pegmatite, albite lepidolite, and greisen. Usually the tourmaline has the phenomenon of colorful ribbon, with colorless line trace, luster of glass, and cannot be separated into slice. Hardness: 7.0-7.5, possessing brittleness, specific gravity: 3.03-3.25, with piezoelectricity and pyroelectricity, the tourmaline shows no or little fluorescence under the shining of the ultraviolet. The red one may send out feeble purple fluorescence. Under the transmission light of the microscope it will show pleochroism.