You're always welcome @ammonite. I enjoy seeing your work very much. You're right, compacted sand is very much like sandstone. I'm reminded of south eastern Canada, where there is this red sandstone that is so soft, rubbing it gently will cause the sand to loosen and come off.
Limestone wouldn't allow for what you want to do and would take many months to produce the size you work in. I've carved limestone, but only about 1 1/2 feet by 1 foot and a bit larger.
Temporary speaks to the reality of this world, so your sculptures make a profound comment on that. I'm very fond of asymmetry, makes for a much more interesting and dynamic work.
I encourage you to continue with NFT's to build on what you're doing. It's a great idea.