I can get in to this I have some inside info on the matter,
First off I worked with granite and marble a good deal in my work, marble is to soft if it's thin you need I bit of thick piece, as for granite it has a lot of tiny little cracks so a one inch thick piece is ife it might break on you I got a 3 foot by 2.5 foot tomb stone head stone, from a nice lady in the biz the thing is four inches thick
I payed $30 for it.
Josh