Where does “simpukka” come from?

simpukka (Finnish) comes from Russian же́мчуг, from Old East Slavic жьмьчюгъ, from Khazar *ǯinǯü, from Common Turkic *yinǯü, from Middle Chinese 珍珠.

simpukka (Finnish): bivalve any species of mollusks belonging to the class; the class Bivalvia