Stalactites, stalagmites, lime-castings and crystallised small lakes, which represent the most beautiful element of the caves, are the final expression of the long work of raining water on the rock. Limestone, in Frasassi, is largely covered with impermeable grounds (Mountain Vallemontagna); raining water doesn't filter in that area but along the breaks : here it transforms calcium-carbonate of the rock in calcium-bicarbonate which is soluble. Inside the cave this chemical process is reversed. Bicarbonate , after giving up CO2 , becomes insoluble and deposits producing wonderful concretions; on the vault, calcium stalactites originated from a small cylinder of calcite where drops passed and then enormously grown.
The concretions at the base of the rooms are called stalagmites, which are the result of the impact of drops on the ground. In the Big Cave of Wind, because of its vastness, the water has to cover a great distance before touching the ground, then it becomes much saturated and besides depositing calcium-carbonate in the impact point, it crusts the around area. This mechanism allowed the formation of giant stalagmites. When concretions increase their size enormously, may meet forming columns of various colour and shape.