Rock candy is a great example of crystallization in a supersaturated solution. Dissolve as much sugar as possible in some boiling water, then allow the solution to cool. To form crystals you need a place for them to nucleate. Tie some string to a weight and lower the string into the solution before it cools. The longer you leave the string undisturbed in the solution, the larger the crystals of sugar. Although rock candy is a crystalline solid, it is not classified as a mineral. Why?