Welcome Camus.

Your discourse is probably above the heads of most of the members here-meaning too technical. Several of us here also have Geology backgrounds or are just really interested in the stuff. So your post isn't lost on us.

Yes slates are found all over and as metamorphosed shale they come in all varieties depending on their makeup and degree of compression.

However I don't think most slates are that great as hones. There are better choices out there in my opinion.