Silly me.
Yes, it does happen in a glass block, except the phenonmenon is very difficult to observe. A more detailed explanation is given here:
http://www.physlink.com/Education/AskExperts/ae184.cfm
Thks for replying anyway.
This question bothered me for some time.
From what i have seen in textbooks, dispersion occurs as soon as white light passes from air into a glass prism, but why not for a glass block, assuming that the angle of incidence is the same?
The standard answer for why dispersion happens in glass...