Sorry to say but I've used T-Rex Bone Aid sand for years on numerous lizards, I've never had an impaction. I know of the very flawed experiment that a young woman on here performed and her data is at best weak. She used large amounts of a calcium carbonate sand that was intended as a cattle food additive, and small amounts of acids. Little wonder it turned into a gooey mess.
To the poster who said that it contains silica, get your facts straight. Play sand is silica and comes from Quartz. Calci Sand is calcium carbonate, the same calcium carbonate that is in your mineral supplement, that is if you use one.
Lizards I have that currently on Calci Sand.
4 Beardies, on it for two years now, no impactions.
3 Mali Uros, 18 months, no impactions.
2 B&W Tegus, 22 months, no impactions. These guys eat a lot of it.
8 Leopard Gex, 3 years, no impactions. These eat it intentionally for the calcium.
1 White Throat Monitor, 1 year, no impactions.
In addtition to not having impactions I've never witnessed what I have with play sand. Undigested play sand in the stools. If anything could cause an impaction play sand would.
Some of the posters here get that bone in their teeth and can't let go. Others read the former's posts and blindly repeat what they read. Doesn't make it fact. The biggest drawbacks to Calci Sand it the expense and certain of the colors stain your lizards. It does need to be changed occaisionally but so does play sand.
If you'd like to perform and experiment try disolving play sand in any strength acid. It won't it's inert in acids. Please don't try to justify it with the "silica sand converts to calcium in the digestive tract" argument. Silica is a pure element and if it can convert to calcium then lead can turn into gold.
BigT