> "a few ten-thousandths of an inch" - close to micro meter precision - sounds almost like exaggeration, but some type of stone might just split in a very plana

> "a few ten-thousandths of an inch" - close to micro meter precision - sounds almost like exaggeration, but some type of stone might just split in a very planar way. Not an exaggeration, just an extremely long time spent hand grinding/polishing with fine grit tools/paste.