I was always confident that diamonds can be broken with a hammer. But my world was shattered when a guy hit a diamond with a hammer and it made a dent on the anvil. A few seconds later the same guy broke it with a comparitively powerless hit. There was definitely something shiny here.
To understand what was going on I had to understand the difference between hardness and toughness.
Hardness is the material’s resistance towards plastic deformation
Toughness is the material’s ability to absorb energy without shattering.
Diamond is extremely hard but not tough enough. You can scratch any surface with diamond but diamond breaks when enough force is applied.
But what about the dent on the anvil? That arises from the fact that the crystal structure has various planar surfaces. Of these planes some split without much energy and others require a lot of energy. Hence,hitting a diamond on its octahedral plane beaks it with a clean cut but on other angles it doesn’t, and dents stuff.
Fun fact, due to its extremely clean cut faces, the diamond face is hydrophobic(doesn’t let water stick) and lipophilic(lets oil stick).
Now that is some crazy physics.