Natron is also the mineralogical name for the compound sodium carbonate decahydrate (NaCO·10HO), which is the main component in historical natron. Sodium carbonate decahydrate has a specific gravity of 1.42 to 1.47 and a Mohs hardness of 1. It crystallizes in the monoclinic-domatic crystal system, typically forming efflorescences and encrustations.