I had an old pool table that I broke apart many years ago. The “slate” turned out to be what appears to be white marble. The pool table was from the 50’s as marble was not in demand back then.
It was 4’ x 7’ but broke in half when I took it out of the basement. I planned on making some kind of outside firepit hearth but have never got around to it.
https://picasaweb.google.com/lh/photo/aX31OHfgHFaF0O0e6tcIzGCp3JoCbi49Uy9XukcR_H8?feat=directlink
It needs to be polished and sealed if used inside for furniture
Free