This superior alloy is made from meteoric iron — specifically, ore refined from meteors that fall during the rare appearances of the comet Alhazarde. Starmetal is extraordinarily hard, and is equal to adamantine for all purposes, including overcoming damage reduction or granting damage reduction when used in armour construction. Starmetal also possesses an inherent magical connection to the Material Plane, meaning that weapons made of the alloy are especially effective against creatures from other planes. Weapons made of starmetal deal an extra 1d6 points of damage to any extraplanar creatures while they are on the Material Plane.
Creating a weapon from starmetal costs 5,000 gp more than creating a similar weapon of steel. Creating armour from starmetal has the same costs as armour created from adamantine.
Source: Complete Arcane (Page 141)