The chemical formula for blue vitriol is CuSO4. Blue vitriol is another term for the compound copper(II) sulfate, when the compound is in its pentahydrate state. This substance can also be called bluestone.
The pentahydrous state for blue vitriol is written as CuSO4·5H2O, meaning that the CuSO4 is hydrated by five water molecules. In this state, blue vitriol is a salt that appears as a bright blue crystal.
As the blue vitriol decomposes, it sheds its water molecules to become anhydrous, meaning that it does not contain any water molecules. Once it is completely dehydrated, blue vitriol appears as gray-white powder.