Cobalt

Cobalt is a material added by Tinkers' Construct and GregTech 6.

Tinker's Construct
Cobalt from Tinkers' Construct is an ore which can be found only in the Nether. It spawns fairly commonly throughout all levels of the Nether in 1-4 block veins.

GregTech 6
As added by GregTech 6

Cobalt from GregTech 6 has two variant: normal Cobalt and radioactive Cobalt-60.