Identification Characteristic of Four Types of White Pearls with Diameter of 8-10 mm from Zhuji Market in China

Freshwater non-nucleated pearls, freshwater nucleated pearls, South sea pearls and akoya pearls are the four common types of white roundish pearls with a diameter of 8-10 mm in the Zhuji market. The authors collected and tested these four types of pearls by microscope, ultraviolet fluorescence, X-ray fluorescence and optical coherence tomography(OCT) for the identification characteristics of these pearls. The results showed that the surface texture of freshwater non-nucleated pearls and nucleated pearls are dim and loose, while South sea pearls and akoya pearls are clear and tight.These four types of white roundish pearls have typical blemish characteristics. X-ray fluorescence testing showed that the ratio of Sr/Ca of freshwater pearls was less than 0.3, and that of South sea pearls was mostly more than 0.35, and that of akoya pearls was mostly in a range from 0.3 to 0.4. OCT testing results showed that the thickness of the nacre layer of freshwater non-nucleated pearls was the most radius among the four types of white pearls with a diameter of 8-10 mm. The nacre layer of freshwater nucleated pearls and South sea pearls were mostly in a range from 1 to 2 mm, while akoya pearls was mostly in a range from 0.3 to 1.0 mm.