Marble for waterline tile

[Mr.Bill]

Hello,
I am building a shotcrete pool. I have a lot of questions. My first is, can I use marble for waterline tile? They are 6x12 inch.

 

[mknauss]

Welcome to the forum!
My concern is that marble is typically porous and sometimes has imperfections. That would not be a good selection for a waterline. You want porcelain tile that is impervious to water for the water line tile.
I suggest you read ABC's of Pool Water Chemistry.