Unlike Mithril which is merely very durable, adamantine is completely indestructible. Adamantine can be exposed to enough Primordium that it undergoes existence failure, but this would also cause the end of that entire plane unless a God, powerful Demon or one of the most able Dark Wizards then contained the Primordium.
It does not conduct heat or electricity at all and cannot be directly affected by magic.
It is about twice as heavy per unit volume than steel.
Adamantine is completely inert, so it is found in 'scales' in its raw form. These are usually found deep under mountains. It can be shaped into items by the attachment of many scales together via magical adhesion.