Opals cracking

[scribblygum]

Amongst all those other perfectly logical reasons for opals cracking, there's also opal bearing areas known for Cracky Opal. Some mines in the Ridge are known to produce opal that looks ok on extrication, but not long after develops cracks all over. Mostly I'd say you'd know about it though, because the cracks happen soon after they're taken out of the ground as people have said before. It has less to do with the water content, and more to do with the pressure. Opals can survive on the surface of the ground dry in the outback for hundreds of years, uncracked, rained on, dried out over and over...so who knows.
I cracked a nice opal that I cut,...I didn't see a crack in it, but must have developed over one of the natural fault lines. I only found it later. Seems to happen. shame.