Your bond with the earth and martial training has imbued your fists with the qualities of cold iron.
Prerequisites: Dwarf, gnome, or goliath, Earth Sense, Improved Unarmed Strike.
Benefit: As long as you are touching the ground, your unarmed attacks are treated as cold iron weapons for the purpose of dealing damage to creatures with damage reduction.
Special: A fighter may select Earth Fist as one of his fighter bonus feats.Source: Races of Stone, page 138.