break: To turn the block into the little floating thing that you can pick up.
destroy: To completely obliterate a block, not even leaving a little floating thing.
Given those definitions, the question is very simple. I had read about TNT mining at another question, but when I tried it, it exposed a solitary diamond. I thought this was odd because I'd never seen one block of diamond ore by itself before, which prompted this question:
Do explosions destroy stuff?