The first step in jade authentication is to identify the kind of material of the object under investigation. According to E. S. Dana 1898’s A Textbook of Mineralogy, jade may mean nephrite or jadeite. Nephrite is a variety of the calcium and magnesium-rich amphibole mineral actinolite. The chemical formula for nephrite is Ca2 (Mg, Fe) 5Si8O22 (OH) 2. And jadeite is a pyroxene mineral with composition formulas presented by NaAlSi2O6. Several major physical characteristics differences between nephrite and jadeite are shown in Table 1.
Table 1 Major Physical Characteristics of Nephrite and Jadeite
|Characteristics Nephrite Jadeite|
|Mohs scale hardness: 6-6.5 6.5-7|
|Specific gravity: 2.95 (+.15, -.05) 3.24-3.43|
|Polish luster: vitreous to greasy vitreous to greasy|
|Refractive index: 1.606-1.632 1.667-1.693|
Material identification of jade can be achieved by looking at the spectrum from a Raman spectrometer or by the refractive index reading via the gemological refractometer such as the GIA Duplex Refractometer. When using the Raman spectrometer, there is a prominent fluorescence peak between 650-700 cm-1 region for Nephrite and Jadeite. For Nephrite, there is an additional water peak around 3700 cm-1 which is absent in Jadeite. This feature allows the user of Raman spectrometer in differentiating between Nephrite and Jadeite. The tool can also be used for identifying jade that has been artificially treated by bleaching, dyeing and polymer impregnation. The common chemical used in the artificial treatment would often add additional peaks to the Raman spectrum.refractometer is used, the refractive index of nephrite is 1.606 to 1.632 via refractometer while the refractive index of jadeite is 1.667 to 1.693.