Calcium and magnesium hydroxide precipitation from alkaline groundwaters in Oman, and their significance to the process of serpentinization

Abstract

Abstract The occurrence and genesis of Ca(OH) 2 and Mg(OH) 2 deposits associated with hyperalkaline groundwater from partly serpentinized ultramafic rocks in Northern Oman is reported. Two types of Ca(OH) 2 deposit are differentiated; crystalline portlandite formed by the evaporation of Ca 2+ -2OH − spring waters, and a form of amorphous gel, not previously known in nature. The latter is a product of present-day low-temperature serpentinization. Mg(OH) 2 (brucite) in both holocrystalline and gel forms is produced by mixing of Mg 2+ −2H surface waters with a Ca 2+ -2OH − groundwater in both surface and groundwater environments. These results indicate that significant differences exist between the processes of medium- and low-temperature brucite generation.