I used some once because I liked the look of it, full of mica chips and such, just different from HD
sand. I boiled it for 2 hours or so, disinfection is key. Then I had to put it in a bucket and test for effects on ph
and hardness over several days.
As stated above, more work than you might want to do, but if your pockets are empty and you have time... not a bad deal.
This sort of thing also gets you out in the woods and streams, which I always recommend!
I ended up going with fluorite about 6 months later, but it caused no problems during the time I used it.