Lithics
While lithic is a broad term referring vaguely to matters relating to stone, in the context of this game lithics refer to knappable pieces of stone specifically. Knappable lithics include flint, quartz, obsidian, and chalcedony.
Lithics can be acquired via the forage lithics
command in specific rooms. Chance of success is determined by the bushcraft skill, and for each recently-foraged lithic, the rest in that same room become harder to find (require a higher roll). While an unskilled forager might only find one or two and then have to move on, a skilled Bushcrafter could find additional lithics in that same room that the novice could not.
A room's lithics regenerate over time, so if a room seems to be all foraged out, one can come back tomorrow to find more - assuming nobody else has come by to forage them already.