You mention "rubbing stones together" as a way to shape hard stone objects -- I agree!
Even better is the combination of processes known to us lithic technologists as, "pecking and grinding".
Actually, it's better described as repetitive alternation of two different processes or working techniques:
- "PECKING": Repetetive "pecking", or "banging" on the surface to be ground away, with a hard, but tough hammerstone. The purpose is to create microfractures that weaken the surface where it is to be ground away. (a properly-"pecked" area is noticeably lighter in color.) When done correctly with matched stones, the hammerstone bounces or rebounds, making it possible to establish a rhythmic cadence, often accompanied by singing. The process is boring, but, when done right, oddly relaxing...
- "GRINDING": rubbing the pecked areas on or with a hard, fine-grained abrading stone -- specifically to remove the previously-damaged area. The pecked areas are noticeably easer to grind away than un-damaged surfaces.
- "REPEAT in new areas needing to be removed...
Final polishing is done by grinding away all traces of peck marks, and can produce beautifully-polished surfaces. Stone materials that responded well to these processes, such as "greenstone" or "bluestone" from MA's "Great Blue Hill" (home of PBS' WGBH) were highly prized, and were traded across vast distances. I once encountered a beautiful, 9" "P&G" bluestone celt on the Red River between TX & OK...
Here are some celts, (pointed-pommel stone adzes or axes) in various stages of the "P&G" manufacturing process:
Anyone who thinks they can achieve similar, controlled results with acid is probably smoking something else highly-prized by Native Americans! '-)