Calcium oxalate

Powdered form of the minerals weddelite and whewellite used in ceramic glazes. A salt of oxalic acid, calcium oxalate can form naturally on calcareous stones as a reaction to oxalic acid excretions of mosses and lichens. In a conservation context, calcium oxalate is generally considered in its role as a form of bioterioration but its cultivation as a protective film for limestone surfaces has been investigated as well.