Rock candy (also called rock sugar) is a type of confectionery mineral composed of relatively large sugar crystals.
This candy is formed by allowing a supersaturated solution of sugar and water to crystallize onto a surface suitable for crystal nucleation, such as a string, stick, or plain granulated sugar. Heating the water before adding the sugar allows more sugar to dissolve thus producing larger crystals.
Crystals form after 6–7 days. Food coloring may be added to the mixture to produce colored candy.