What type of mixtures are separated by the technique of crystallisation?

Crystallisation method can be used for the purification of those mixtures which:
i. contain soluble impurities. [0.5 Mark]
ii. contain solids that decompose on heating. [0.5 Mark]
iii. have solutes that are crystalline in nature. [0.5 Mark]

For example: Salt obtained from the sea is separated from its impurities using crystallisation, pure crystals of alum (phitkari) are obtained from its impure samples by using this method. [0.5 Mark]