fluorescein: a yellow dye that is visible even when highly diluted; used as an absorption indicator when silver nitrate solution is added to sodium chloride in order to precipitate silver chloride (turns pink when no chloride ions are left in solution and negative fluorescein ions are then absorbed)
dye: a usually soluble substance for staining or coloring e.g. fabrics or hair
petrifaction: the process of turning some plant material into stone by infiltration with water carrying mineral particles without changing the original shape