Originally Posted by agrostis
You are correct. Any sand that has micro and macro pore's is going to hold moisture better than sand that has had those pore's worn away by the grinding action of being under water. The only way to really tell is to look at that sand under a microscope. Some application's that need sand that has pore space are brick layer's and golf course builder's (for putting green's). Sand's that meet those requirement's are mined on dry land. River sand is cheaper (but not by much) and much more common. If you topdress your yard once or twice a year you won't notice a difference but if you topdress once a month you will. Personally, i woudn't buy river sand. For all that work and expense, i want sand that hold's moisture, but if river sand is all that available in your area, then your choice's are limited, some area's just don't have sand's like that. But like i said, if you only topdress once or twice a year you will never notice the difference. And if your goal is to level out a lumpy surface then a sand's pore space isn't the main concern anyway. A thin layer of sand make's hardly any difference in a yard's ability to hold moisture. When you talk about sand, angular, sharp and masonry sand all mean the same thing, or should, pore space.
In all the years I've worked with soils and studied their characteristics (especially sands used for building construction, golf course construction, and athletic field construction), I've never heard of sand particle shape or origin having much to do with water holding capacity. Particle size can certainly impact water holding capacity, but particle shape and origin usually have little to do with it.
There's not really much need to worry about how much water your topdressing sand can hold, since you're just making a layer on top of the heavier soil you already have, which already holds plenty of water. When you accumulate organic matter from plant growth, you'll have plenty of water holding capacity.
This whole thread is looking like an exercise in overthinking a problem and some guys are seeing poor results from not properly understanding what they're doing.