Ok, I guess the video made by somebody that I can no longer find showing mats being collected from "small rocks" was wrong then - they must have been bronzite chondrites or metallic meteorites or whatever.
However, I'd say you're wrong about the wave scanner never giving signals that appear to comer from ordinary rocks as I've seen strong signals appear quite a few times when driving around (and no, I don't mean the signal from the ship, in case that's what you're wondering,) but when I have driven towards those signals, no targets pop up and the signals soon disappear.