Sorry, I can't help with the distinctions, but I'm curious about how you use the stuff. I've been digging sand into my very clayey soil recently, after years of adding compost and still having the dirt harden on me as the season advances. I've run into some real disagreements about the value of adding sand; some experts say it will lead to cement-like soil, others advise it. One did say to use sharp sand (I can't remember if it was printed as one word) rather than river sand, because the edges on sharp sand will allow for better drainage. Me, I've got my fingers crossed...

Kate