By @rockpowell : A VERY EXPENSIVE LESSON - Watch out for fractures!
Just to let you know what happened to me !!
I was putting this small blue agate rock in my vice on the rock saw, as I tightened it down I heard a CRACKING noise, but I kept going, didn't stop and take the rock out and check it. I started to saw the rock and then Bang zing. Was standing right there, stopped the saw -- and this is what I saw - the rock had broken in half and flipped the back part of the rock out and took a big bite out of my new 3 months old saw blade.
Dang !!!!! Sh%@t happens if you're not paying attention. Just a very expensive lesson, thought I would share it with you.