Cracked Pedestal Sink

[Sam Leon]

What could cause a pedestal sink to crack all the way around it's "rim"?

This sink has been around for years and suddenly a crack has developed all the way around it's perimeter.  Tenants says nothing has happened.

What could have caused it?

It's not a new sink, and this happened all of a sudden?

I don't think a hammer falling on it would crack it like this?  Any idea?