Whewellite, or at least crystalline calcium oxalate, does also arise from natural sources. Small crystals or flakes are sometimes found on the surfaces of some cacti, and kidney stones frequently have the same composition.
Whewellite is used as a thermogravimetric analysis standard due to its well known decomposition temperatures and products.
On Human Blood, Rock Art and Calcium Oxalate: Further Studies on Organic Carbon Content and Radiocarbon Age of Materials Relating to Australian Rock Art
Jun 01, 1997; Loy et al. (1990: 111) reported an AMS radiocarbon determination of c. 20,000 b.p. (RIDDL-1270) from a rock-art site at Laurie...