The hardness of the stones carved by the ancients

Let's answer this question. We cannot give a quantitative standard of hardness. Answer completely by feeling, whether you like it or not.

As far as I know, the stones used in ancient inscriptions should be mainly sedimentary rocks, specifically shale and bluestone. The reasons are as follows: first, too hard rocks, such as magmatic rocks, are not conducive to processing (making tablet surfaces), and it is difficult to engrave words, which affects efficiency. Secondly, the ancients carved stone tablets either to commemorate their ancestors or to record some important events, and some of them were calligraphy works. However, whatever the reason, they all hope that the branch stone tablets can be preserved for a long time. From this point of view, metamorphic rocks (mostly) are less hard and easy to be eroded and weathered, which is not conducive to long-term preservation. So in general, sedimentary rocks are more suitable. Of course, it is not clear what the specific hardness index is.