Kaito doesn't have a pickaxe to mine the Moon Crystal, but even if he did he wouldn't use it. The clang of the pick hitting the stone would echo not only throughout the chamber, but also through a good part of the tunnels he'd traveled through, and that would definitely be more than enough to wake up the Orc standing a few meters away from him.
For this reason, while the monster's deep snoring seems to shake the whole cave, Kaito, with his small knife, fits the tip of the blade into a small gap and tries to delicately extract a Moon Crystal or at least the fraction of one.
This is a job that requires a lot of care, because if Kaito pushes too hard, he'll break the stone and make a noise, and if he doesn't push at all, he won't be able to remove the Moon Crystal from the rock. And as simple as it sounds, mining isn't easy, because it requires attention not to damage the gem either.