Sodium carbonate
Sodium carbonate decahydrate is stable at room temperature but recrystallizes at only to sodium carbonate heptahydrate, Na2CO3·7H2O, then above to sodium carbonate monohydrate, Na2CO3·H2O. This recrystallization from decahydrate to monohydrate releases much crystal water in a mostly clear, colorless salt solution with little solid thermonatrite. The mineral natron is often found in association with thermonatrite, nahcolite, trona, halite, mirabilite, gaylussite, gypsum, and calcite.