Centimeter-sized crystals of orthorhombic calcium formate, α-Ca(HCO₂ )₂ from Alkali Lake, Oregon, USA have been studied by means of powder and single-crystal X-ray diffraction analysis, infrared, and Raman spectroscopy. Based on the data on carbon isotope abundance in calcium formate and associated minerals, it was concluded that the formation of α-Ca(HCO₂ )₂ may be a result of a combination of two factors: lake microbial metabolism and anthropogenic pollution with Agent Orange. Possible causes of stability of the low-density tetragonal β-Ca(HCO₂ )₂ polymorph (formicaite) in boron ores are discussed.