Starmetal

This rare alloy is sometimes found in meteors. Starmetal is extraordinarily hard, and has all the same properties as adamantine. Starmetal also possesses an inherent magical connection to the Material Plane, giving it numerous applications. Due to its extraordinary properties and rarity, it is priced at 1.5 times adamantine.
Weapons made of starmetal deal an extra 1d6 points of damage to any extraplanar creatures while they are on the Material Plane. Starmetal armor gives bonuses to AC vs natural weapons used by extraplanar creatures while they are on the Material Plane, or other weapons made from materials alien to the Material Plane.

Armor Category	AC Bonus
Light	+1
Medium	+2
Heavy	+3

Properties

Material Characteristics

This silvery metal has just the slightest tinge of green.

Physical & Chemical Properties

As hard as adamantine. Has innate magical properties and a connection to the material plane.

Geology & Geography

Can be found anywhere across the world, potentially inside any meteor.

Source
D&D 3.5, Complete Arcane p141