Diamonds have a grain similar to the grain in wood.
It is easier to cut with the grain than against it. You can cleave diamonds with the grain using an axe, but you have to use a saw to cut across the grain. A diamond also has impurities - sort of like knots in wood. An axe is a hard metal blade which is struck with a wooden or metal hammer using a sharp blow. A saw is a paper-thin disc of phosphorbronze few inches in diameter impregnated with diamond dust.