Adamantine

Also, known as "Titan-blood" or "Star-blood" by some cultures, the adamantine metal is actually an alloy of Adamant and some other metals made in a special furnace that is capable of higher temperature than a normal one. When it is ready, it can be used in a normal smithy to craft weapons and armor or other items. The ore itself is said to come either from the stars (some meteors would carry it with them, crashing into the planet) or from the Titans from the First Age, The Titan War. All items created by the jet-black metal would become magical, in a sense. Weapons would have easier time destroying and sundering objects on their path (except those made out of adamantine). While armor could save the wearer from a fatal blow that would bypass a normal steel armor. However, the metal is almost three times heavier than normal unless it is made by a master crafter, who how to weave the metal to still have its properties but not weight as much.

Properties

Weapons made from Adamantine weigh one and a half as much and gain a Strength 13 requirement, however, if they already have a Strength requirement, increase it by 2. Adamantine weapons add an additional die of damage when a critical hit is made and they count as magical for the purpose of overcoming damage resistance. Also, they do double damage against objects (creatures of the Construct type don't count as objects), unless they are made of adamantine too. Add 500 gold pieces to the base price. Non-metal weapons can't be adamantine.
Armors made from Adamantine weigh one and a half as much and gain a Strength 13 requirement, however, if they already have a Strength requirement, increase it by 2. Adamantine armor makes critical hits against the weaver count as normal hits. Non-heavy armor adds 2000 gold pieces to the base price, while heavy armor adds 4000 to the base price. Non-metal armor can't be adamantine. 
Shields made from Adamantine weigh one and a half as much and gain a Strength 13 requirement, however, if they already have a Strength requirement, increase it by 2. They negate the qualities of Adamantine weapon attacks made against the user. Add 300 gold pieces to the base price. Non-metal shields can't be adamantine.