Carbonate accumulation on islands in the Okavango Delta, Botswana.

Efflorescent crusts consisting predominantly of the sodium carbonate minerals trona and thermonatrite with minor sylvite are commonly developed on less vegetated portions of islands where the land surface is less than about one metre above water level. This efflorescence represents the end product of evaporation of swamp water. At intermediate stages of evaporation, small calcite crystals are produced. These are brought to the surface by ants for the construction of termitaria, degradation of which produces concentrations of calcite on the surface. -from Authors