We have done as much as 100% replacement of sands with glow stone. We did it on a few small tables, have yet to see any issues with them.
For some slurries we did 50% glow powder with 50% cement, it worked fine.
Basically it is a resin sand, in my mind. The replacement amount would really depend on how much glow you wanted. The higher the amount the more glow. Even 50% of you sands would look pretty cool I think.
Or you can do what Jon said.
I would tend to agree with Jon as well, but would still like to see some silica sand in there, mostl for compression strength (if needed). AGT is one of my sponsors and I can try to get some answers if you like or put you intouch with the right pweson to get those answers. Let me know.