A stick of rock was a delightful thing to me as a child, and no holiday was complete without at least one.
Like you, if I were to read "rock candy" I would think the candy had been "stuck on" to the rock for clarification purposes, possibly US usage. I would certainly not in my wildest dreams associate it with Kandiszucker.
Having written that, guess what my Collins offers as a translation for Kandiszucker (without the AE qualification)!
That got me curious, so I looked rock candy up in my OUP English dictionary, which says:
noun [mass noun] N. Amer. a kind of hard confectionery typically made of masses of crystallized sugar.
Now that's interesting, that sounds like a description of our rock. Where does Kandiszucker come in here?
Wikepedia's entry might help:
"Rock candy is a type of confectionery composed of relatively large sugar crystals.
Homemade rock candy is commonly formed by allowing a solution of sugar and water to crystallize onto a string or some other surface. Superheating the solution by boiling the water before adding the sugar can help produce larger crystals. Crystals form after several days. Food coloring is often added to the mixture to produce colorized candy.
Rock candy is a different product from British rock, also called "seaside rock", which more closely resembles a candy cane. The word "candy" is not usually used for confectionery in the UK."
I found this picture:http://www.exploratorium.edu/cooking/candy/re...
Since my Duden says that Kandiszucker is "an Fäden gebildete Zuckerkristalle", rock candy probably is the closest you can get to Kandiszucker, except you can't get it in red or green here (or not in Edeka, anyway!). The main difference would seem to be that in America it's a type of sweet and in Germany something you put in your tea, but from actual looks, it's the same. Well, apart from the colour.
I wonder if Kandiszucker would be rock sugar in the UK? I haven't lived there for such a long time that I don't know. But I'm sure someone out there does!
Haven't I confused the issue nicely! What it boils down to is that AE should definitely be appended to rock candy as a translation for Kandiszucker.
I'll stop putting off working, now, and go and get on with my translation...