From Dwarf Fortress Wiki
Cobaltite is a brilliant blue stone (notably, the only stone of its color) found as veins in numerous environments. Despite its appearance (showing up as
£ unmined and
* mined), it is not a usable ore.
[INORGANIC:COBALTITE] [USE_MATERIAL_TEMPLATE:STONE_TEMPLATE] [STATE_NAME_ADJ:ALL_SOLID:cobaltite][DISPLAY_COLOR:1:7:1][TILE:156] [ENVIRONMENT:IGNEOUS_ALL:VEIN:100] [ENVIRONMENT:METAMORPHIC:VEIN:100] [ITEM_SYMBOL:'*'] [SOLID_DENSITY:6295] [IS_STONE]