Crude copper sulfate is a mixture of copper sulfate with various impurities that may include copper carbonate, copper oxides, and other copper compounds. To crystallise copper sulphate, dissolve it in water and add a small quantity of dilute sulphuric acid to prevent the hydrolysis of copper sulphte. The impurities left behind in the solution are removed by filtration. The filtrate is concentrated to the crystallisation point and then cooled. On cooling, transparent blue crystals of copper sulphate separate. The copper sulphate crystal formed has triclinic shape.
This video explains how to prepare the crystals of pure copper sulphate form an impure sample through crystallisation.