A simple hard candy made by allowing a concentrated sugar syrup to evaporate slowly (sometimes for up to a week), during which time it crystallizes into chunks. The crystals can be formed around strings or small sticks (the latter can be used as stir sticks for sweet drinks). Small rock-candy crystals can be used as a fancy sweetener for tea or coffee. rock and rye liqueur has a large chunk of rock candy in the bottom of the bottle. Rock candy can be made at home or purchased in candy shops.