I would get another bar of clay and trash that one. I went downstairs and checked my two clay bars and the one (Meguiar's) that's been sitting in the jar for about two years, and there's no cracking. If the clay is too dry (cracking) it may scratch. This is only my interpretation of what dry clay might do ... but I wouldn't use it.
DISCLAIMER: I've never used Blackfire clays so I'm kind of talking out of my butt. I'll be following this thread to see if others have different opinions/experiences.
