Thanks for the spoiler, Akroma. Now he won't learn it the hard way, with no legendary dwarves.
Unless, of course, they use the adamantite. I've heard it sometimes gives legendary even when possessed, though it might be a bug.
Also, it's best to time the opening of the cavern to be simultaneous with a goblin siege, so you get a lot of metal to melt down and use for stuff if one of your dwarves gets lucky and uses adamantite in his artifact.
Of course, this only applies if he is some sort of metal dude.
Now, you might be wondering how you're gonna protect your fortress without a military. Well, the answer is simple.
You train SOME (like, five) military dwarves. I remember that being the maximum before it stops the "cake". Give them maces, and make then charge headlong into the goblins. Don't worry, they'll run away. The goblins that is.
Now, if they run away, how do you get the metal?
Simple!
Observe:
code:
____________
_
_ g
_ g D
BB g D
_ g
_ g
____________ g = goblin
D = dwarven forces
BB = retractable bridge
_ = channel
First you let the goblins in over the bridge, into the channel thing.
Then you retract the bridge, so that the only way to escape is behind the dwarves.
They'll run to your dwarves to be slaughtered without a fight. Trust me.
I've used it many times, and I've never lost a soldier.
The goblins carry a lot of iron stuff, however, so you might get a lot of immigrants next year.