This is a somewhat belated response to this line in inquiry. If it
duplicates what someone has already said, I apologize.
The glass block floor that I know best is in the stacks at the Library
of Congress. In the good old days when researchers could get stack
passes, I remember being VERY nervous about walking around on these
odd, translucent floors. The Library dates from some time in the
1890s, I think.
I don't know whether they are still there, since the Library has
recently been "restored" at great cost.
I have a feeling that I have seen these glass block floors in other
library stacks as well.
Marilyn