Cinnabar is a brilliant red stone found as veins in numerous environments. Despite its appearance (showing up as
£ unmined and
* mined), it is not a usable ore.
Cinnabar is also the most dense non-economic stone besides slade, so it's very good for stone-fall traps and as catapult ammo. Hauling cinnabar is not realistic, or at least will take an eternity, without a wheelbarrow. Additionally, cinnabar crafts are so heavyweight they can fill up a caravan.
 In Real Life
Cinnabar is a mineral of mercury sulfide (HgS), and has been used throughout history both for the ease in which it can be made to release its elemental mercury, and for use as a red pigment in paint. In ancient Roman history, slaves or prisoners were consigned to cinnabar mines as a death sentence - unlike humans, dwarves are evidently immune to mercury poisoning.
[INORGANIC:CINNABAR] [USE_MATERIAL_TEMPLATE:STONE_TEMPLATE] [STATE_NAME_ADJ:ALL_SOLID:cinnabar][DISPLAY_COLOR:4:7:1][TILE:156] [ENVIRONMENT:IGNEOUS_EXTRUSIVE:VEIN:100] [ENVIRONMENT_SPEC:SHALE:VEIN:100] [ENVIRONMENT_SPEC:QUARTZITE:VEIN:100] [ITEM_SYMBOL:'*'] [IS_STONE] [MELTING_POINT:11044] [SOLID_DENSITY:8100]