Natron
Sodium carbonate decahydrate stays the same at room temperature, but it changes into the crystal material Na2CO3·7H2O, then above  to sodium carbonate monohydrate, Na2CO3·H2O, if the temperature becomes . This releases a mostly clear, colorless salty kind of water with a little solid thermonatrite. The mineral natron is often found in association with other minerals such as gypsum and calcite.