Which actually makes me wonder if those aren’t fiat, too, considering artificial scarcity (De Beers and diamonds, for example).

I can see an argument for considering them fiat. The value of "high-value assets" (e.g. gold) comes from the assumption they'll retain their value even if things get drastic, not from being immediately useful (e.g. alcohol) or necessary to survive (e.g. water).

PMs

Zero clue what the acronym means in this context.