My curiosity finally got the best of me. So, I headed to a Leslie Pool Center a few blocks away and purchased a 25 pound bag - about $25 with the tax.
To see what was in the bag, I opened it and scooped out a handful onto a white plate:
It is advertised as being from about .5 mm to 2 mm dia pieces, and it looks like it is. It has a faint green color when dry, and looks a bit dusty. So, I added some water to the plate to see how it looks wet:
It just looks like a medium grey color when wet, and doesn't generate a lot of cloudiness - far less than Soilmaster does. This could be expected since this stuff is sold to be used as a filter sand in a swimming pool filter.
Now, my curiosity is burning some more! I know I will be using this in a tank before too long. The idea is extremely appealing! And, the 25 pounds looks like nearly a cubic foot in volume, which would be about 3 inches deep in my 45 gallon tank. If I add another inch to this, made up of river bank silt, its enough for the tank - all for $25.
Then I could try the emersed start to a tank, too! But a few more questions: are the grains sharp enough to harm digging fish, like Cory Cats? Does it affect the KH or GH? Does it need a cap of something else? Would it be easy to plant in?