Is it safe to hold silicon nitride ceramic without protection?
I have a few silicon nitride balls in my drawer. They look pretty cool, that's why I keep them and touch them all of the time.



It is a very hard, glasslike material. It won't be easy to crack. There is nothing coming off the surface, ball bearings have extremely smooth surfaces (nm roughness), if anything would rub off, they would not be usable as ball bearings. Besides that, I don't think it is toxic. It is an extremely inert material, much more inert than steel, does not dissolve in much. It is even used in prosthetic parts that go into the body. I assume it needs a lot of certification for that.

If you break it (which won't be easy), you'll have some sharp pieces that might cut you, that's all.

The only risk would be from a ball bearing that was ground to a very fine dust.