Turquoise Water in a Limestone Mine

Clear turquoise water is often associated with tropical beaches. An open cast mine is probably the last place one would expect to find clear blue or turquoise water. The pictures below were taken at the Aruwakkalu Limestone mine in Puttalam Sri Lanka.

When limestone is excavated from the base of the quarry, and when the excavated pit reaches the ground water table, water starts seeping in. It is this water that has a spectacular turquoise colour. The reason for this colour is not the blue reflection of the sky like in the case of seas and lakes. It is due to the scattering of light by minute Calcite crystals.

Limestone is essentially Calcium Carbonate and the water in the limestone pit contains a large amount of it dissolved. Once the water gets saturated by calcium carbonate, it starts to crystallize and forms very tiny crystals which remain dispersed in the water. This crystalline form of calcium carbonate, is known as Calcite. These micro Calcite crystals scatter light selectively giving it a turquoise colour.

Since Calcium Carbonate is alkaline, this water has a high pH value. Therefore, as inviting as it looks, taking a dip in this water is not advisable. Prolonged exposure to water with a high pH can cause skin and eye irritations.