Limestone frequently is used in floors, countertops, pillars and other construction applications. Limestone generally is considered attractive, is available in multiple colour options, and it also an extremely durable stone. Limestone can last a lifetime if it is properly maintained. It is susceptible to scratches if it is struck hard enough or something is dragged across it. Deep scratches usually require professional repair but small scratches can be buffed out or covered up.
Wash the area around the scratch with warm water and a mild dishwashing soap.
Buff the scratch with a light steel wool. Steel wool is numbered in accordance with its coarseness. You want the lightest kind, which is numbered "0000." Heavier steel wool is more likely to damage the surface.
Colour over the scratch with a black permanent marker or a paint marker if your limestone is darker coloured. This will cover up the scratch so it is not noticeable. Remove any excess colouring by wiping around the scratch with a cotton ball soaked with denatured alcohol.
Deeper scratches need to be treated by a stone professional to restore the limestone to its original state. Trying to repair severe scratches yourself without the experience and the equipment of a professional is more likely to make the limestone scratch worse.