Sodium sulfite heptahydrate  -  Na2SO37H2O

 

 

Sodium sulfite comes as anhydrous solid and as the heptahydrate. The heptahydrate forms beautiful hexagonal crystals, which, however, slowly loose water of crystallization and becomes a powder. The sample, shown here, clearly shows the hexagonal crystals, but one can also clearly see that the crystals are covered by a layer of powder.