Freshwater Pearl Classification
Gray, White, Cream, Yellow, Pink, Purple With Blue, Green Overtone, Orient
Appearance, RI, birefringence blink and magnification. A "tooth test" is commonly used in which a pearl is rubbed against a tooth; if gritty, this is an indication that the surface is nacre, versus plastic and glass imitations that feel smooth.
Typical size of freshwater pearls are 2 to 13mm. They are produced by the Hyriopsis schlegeli, Hyriopsis cumingli and Cristaria plicata mussels. Kasumiga pearls were farmed in the Japanese Lake Kassumigaura in the hybrid Hyriopsis schlegeli/ Hyriopsis cumingli mussel.