Belgian Black marble
This black ‘marble’ is in fact a fine-grained Lower Carboniferous limestone able to take a good polish that was quarried both in Tournai, France and Namur, Belgium. An article in Science Direct on the web has a good description. We have several tomb slabs in Dorset. Lytchett Matravers, Wimborne Minster and Sturminster Marshall come immediately to mind. It has been referred to as ‘Belgian Black’, or the ‘Tournai Marble’ found in some fonts. A table top to a tomb in Winterborne Stickland could be another example.