Headstones are sometimes made of slate, at least in the U.S. That has the disadvantage that the layers sometimes split apart. But it has the advantage that, if the stone manages to stay in one piece, the inscription does not weather in the least. Go to an old graveyard in this country, and you will see that on slate stones the inscriptions are still perfectly sharp even after 250 years -- even the scored guidelines are still visible -- whereas on a marble stone after 100 years the lettering is so washed out as to be illegible. The marble, I suppose, was prettier at the beginning.