Hi Robert,
Please know that I have very little experience with "impacted" animals. That being said, I keep my monitors and sub-adult/adult beardies on sand that is naturally derived - in some cases I go and dig it up myself. I am not sure about whether the jagged edges lock the particles up or not - doesn't sound unreasonable. I just don't want my animals swallowing little sharp pieces of glass on a regular basis. In nature these animals live on dirt/sand and you can be sure they ingest a reasonable amount of it over the course of their lives (no paper towels and shelf liner out in the bush). But that dirt/sand is again "natural" and has been worn smooth. I speculate and it has been my experience that the animals don't have trouble passing such material. I'm sure if any animal swallowed something the size of a boulder it could be a problem.
On the other hand, I just cut open a baby beardie that I had pass only to find a large particle of sand (natural sand) in his belly. Was that the cause of his death? I don't know. He had some symptoms that may indicate such was the case. I did switch the babies over to paper towels in case and for ease of care. Also, the sand I had many of the babies on was sometimes larger than the finest of fine. I know other folks have had good luck keeping babies on fine sand.
It is my opinion that it is not an issue with the larger animals (sub-adults and adults).
So there's a response much longer than you wanted
.
Good luck with your animals and take care,
Ian