Mandarin pearls are the unique name given to chinese pearls drilled as buttons so they could be used to adorn clothing. These uniquely drilled pearls were used to adorn the hat of mandarins.
Confused? I was. The term mandarin, as most of us know it, refers to the spoken form of Chinese language, a language specific to certain northern and southwestern regions of China. And, of course, there is Mandarin Chinese food which are popular dishes from these specific regions. But what ended up being the name of a the Chinese dialect originated from the group of people who spoke this language. This group was the mandarins.
Mandarins are government official. In fact the word mandarin is literally translated into "speech of officials." Although this name did not become popular until the 1500s, the official use of "civil servants" originated in China during the Zhou Dynasty (1046–256 BC). Back then most individuals became designated officials based on their relation to the nobility. By the Tang Dynasty (618 – 907 AD) an actual ranking system was put into place based on specific tests. The mandarins had a very strict protocol for dress, similar to military uniforms, and certain adornments that were allowed based on position and rank. Up until the 19th century, pearls were used to adorn both the caps and dresses of mandarins.
These Mandarin Pearls were double drilled to make them easy to sew on. They were a show of rank and were used rather lavishly. The last emperor of China wore a head dress crowned with pearls.
Due to the double drill holes, these pearls are thought to hold less value than single drilled pearls although they look lovely in jewelry settings and have been known to be "reused" in ring settings so the holes are not visible.