Rock candy or sugar candy, also called rock sugar, or crystal sugar, is a type of confection 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 to 7 days. Food coloring may be added to the mixture to produce colored candy.
For the Chinese cooking sugar, see rock sugar.