I'm writing a sci-fi story that has a company that does deep-sea mining. Maybe on this planet, maybe some other aquatic alien planet, it doesn't really matter.

When I research about real deep-sea mining, I read about rare earths and things like that-- but they're too cost-prohibitive to really pursue with current technology.

When I start trying to look up rare, valuable minerals that would be worth the effort, I keep running into qualities like "corrodes in water" or "unstable in water" or "catches fire in water" or whatever. :P So I don't want to accidentally pick the wrong thing that would make a reader go, "What?" if I talk about how it gets dredged from the mud, etc.

I can be obvious and boring, and do something like deep-sea gold, or deep-sea diamonds, or something instantly recognizable as "Oh, that's valuable." Or I can be make up my own element/mineral that people of the future rely on for some sort of technology.

But is there something that's a bit arcane, but perhaps even more valuable than diamonds or gold, that I could pick instead, that would sound a bit more science-y and less generic-adventure-y?

Suggestions are appreciated!