What is the difference between rock sugar and raw sugar?
Rock sugar would be chemically the same as regular granulated sugar, but in the form of huge crystals. Some people call it "rock candy", and you can make it, slowly, at home by growing crystals in a syrup made of granulated sugar and water. How it is made at large scale, commercially, I have no idea.

See wikipedia, https://en.wikipedia.org/wiki/Rock_candy. They have a picture: