whewellite

{{Infobox mineral | name = Whewellite | boxwidth = | image = Whewellite-md82a.jpg | alt = | caption = A white Whewellite crystal from Schlema, Germany | category = Oxalate minerals | formula = CaC2O4·H2O | IMAsymbol = Whe | molweight = | strunz = 10.AB.45 | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/c (no. 14) | unit cell = | color = Colorless, yellowish, brownish | colour = | habit = Equant or stout prismatic crystals | twinning = e {01} twin plane | cleavage = {01} good, {010} imperfect, {001} indistinct, {110} indistinct | fracture = Conchoidal | tenacity = Brittle | mohs = 2.5–3 | luster = Vitreous to pearly | streak = | diaphaneity = Transparent | gravity = 2.23 | density = | polish = | opticalprop = Biaxial (+), colorless (transmitted light) | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Insoluble in water, soluble in acids | impurities = | alteration = | other = | prop1 = | prop1text = | references = }}

Whewellite is a mineral, hydrated calcium oxalate, formula Ca C2O4·H2O. Because of its organic content it is thought to have an indirect biological origin; this hypothesis is supported by its presence in coal and sedimentary nodules. However, it has also been found in hydrothermal deposits where a biological source appears improbable. For this reason, it may be classed as a true mineral.