Koshering Marble Countertop and Sink

Peace and blessing! How does one kasher marble countertop and a sink? And is there a type of marble countertop and sink that cannot be kashered at all?

Dear …!
Stone and metal can be kashered.
Earthenware, ceramic, plastic cannot be kashered.
A sink often contains absorbed spillage of boiling gravies from a primary vessel (that is, a vessel that was heated on a fire or by an electric element). Therefore if it is of the type that kashering is effective on, and it was used with forbidden foods or meat and milk, one should pour boiling water on it from a pot or kettle in which the water was heated.
However, if the sink is of a type that cannot be kashered, one should not use it for food or utensils at a temperature higher than the temperature that “the hand recoils from” - about 40 degrees Centigrade (104F).
Marble countertop — it is uncommon to use it in a way that boiling foods are poured on it, therefore there is no need to kasher it.