I did a general search, and I also checked the main page of this post, and as far as I can tell, noone's mentioned salt/salt mines. I was surprised (maybe Search isn't working properly? It only brings up two posts, and includes basalt). Not only would this be extremely valuable as a resource (to preserve food, and maybe corpses), and as a luxury, it seems like it demands special attention, being more akin to a gem or a metal than a "common" rock.
I could see salt being combined with meat to produce more valuable preserved meat, or just combined with other foods, for variety, and salt being a requirement for producing things like buckskin leather. It might even be something your dwarfs could bring to their wounded (along with honey, maybe?), to help the healing process.
Salt might also be washed away by water flows, so that, where you once had solid rocksalt, a few years later, you now would have brand new caverns. Ofcourse, in the real world, this probably would happen over aeons, but it might make a nice special event to have new caves suddenly but naturally open up, in a few months' time.
There might be exotic critters and special undead living in salt areas, too, and dwarfs might get dehydrated faster in salt areas.