Wikipedia
Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula CaCO. It is a chemical compound that forms envelope-shaped crystals, known in plants as raphides. A major constituent of human kidney stones, calcium oxalate is also found in beerstone, a scale that forms on containers used in breweries.
Usage examples of "calcium oxalate".
A second stone, a calcium oxalate crystal, to be precise, lodged in his ureter and, like a pirate radio station, went on the air with a sporadic signal and a musical format programmed by Nazi biologists and prelates from the Inquisition.
Other constituents are a crystalline saponin- like glucoside, an amorphous, bitter glucoside, which is a modification of tannin, and is known as Ipecacuanhic acid, choline, resin, pectin, starch, sugar, calcium oxalate, odorous, fatty matter and a disagreeable-smelling volatile oil.
Microscopic examination of the tissue of the bark shows round starch grains and very characteristic twin crystals of Calcium oxalate.
Other constituents of Henbane are a glucosidal bitter principle called hyoscytricin, choline, mucilage, albumin, calcium oxalate and potassium nitrate.
Perhaps it picked up iron from the soil, as horsetails pick up calcium oxalate, or some prairie grasses pick up selenium.