CaC2O4


calcium oxalate

A simple chemical that may crystalise in renal tubules and a common component of kidney stones. It is more commonly present as a monohydrate or CaC2O4•H2O, whewellite, than as a dihrate or CaC2O4•2H2O, weddellite, which appears in normal urine and in tissues after exposure to ethylene glycol.
Source
Tropical house plants, rhubarb, Oxalis, Araceae, taro, kiwifruit, tea leaves, agaves, alocasia and spinach.