It is also fairly soft and fairly easy to carve. Slate tombstones that are hundreds of years old can usually be easily read. In the past 100 years, though, most American tombstones have been created from two other types of rock. First to marble. Marble is a crystallized form of what began as limestone, a chemical precipitate formed as layers in the bottom of a shallow sea.
Marble is, like slate, relatively soft and quite easy to carve.
It is fairly easy to saw and grind, which is good since it doesn't cleave like slate. If you've ever been to a U.S. Military cemetery, virtually all tombstones you see in the long precise rows are marble. The effect is quite striking. Marble, unfortunately, does not resist chemical weathering at all well. As the process continues, tiny flecks of marble spall off the stone, leaving a white, sugary, irregular surface behind.