Back in the mid-60s, I tried to break a diamond disc, just to see what it took. [It was an unplayable one that I had already replaced with a good copy.] I stood at the top of the stairs going to our basement, and tossed it down----it chipped a little and bounced. Over the knee didn't even begin to do the job. After several attempts, I put it on two concrete blocks spaced about 6 inches apart and hit it with a sledge hammer. THAT'S what it took to break that disc! If only our other records were so indestructible.
Bob Ault