I'm not positive on the stats off the top of my head but I gave a few to Tiddeggur in Crossing, should have them in his shop - Note, they are darkstone. Pretty sure they are the only ones that exist at this time but not positive.

Codiax.
Forged Weapons:
http://www.elanthipedia.org/wiki/User:Codiax#Codiax-Forged-Weapons

>>how does darkstone compare to other "rare metals?"

Same stats as midsteel. So a little less than high carbon steel but i don't think anyone will be able to craft those for quite some time.

Codiax.
Forged Weapons:
http://www.elanthipedia.org/wiki/User:Codiax#Codiax-Forged-Weapons