|This article is about an older version of DF.|
Rock salt is a Sedimentary layer. It can contain large clusters of Magnetite as well as veins of Bituminous coal. Being salt, it is very likely that your dwarves will grind small bits of it up to put on or in their food, even if you don't get told this explicitly.
[MATGLOSS_STONE:ROCK_SALT] [NAME:rock salt][COLOR:7:7:1][TILE:'#'] [SEDIMENTARY] [SOLID_DENSITY:2100]