* Its promoters, in the early nineteenth century, claimed it resembled the fine freshwater limestones quarried on Portland Bill in Dorset, southern England.

† In simplified form, CaCO₃ > CaO + CO₂. In reality, Ordinary Portland Cement contains silicates: 5CaCO₃ + 2SiO₂ > (3CaO, SiO₂) (2CaO, SiO₂) + 5CO₂.²¹

‡ 222kg C × 3.667.