...I'm sure you've already determined this, but you'll want to protect that at all costs. If your physical form takes too much damage, you'll simply retreat back into your Gem to recover; however, if your Gem gets damaged, you'll start losing control.

...Fortunately, I've been told that we do have countermeasures. Apparently, while our healers cannot completely mend the corrupted stones, they can heal cracks and fractures we incur. Still, it's important to get those treated as quickly as possible, for obvious reasons.