Adamantium is a virtually indestructable man-made steel alloy which does not occur in nature and whose exact chemical composition is a United States government classified secret. Adamantium is not an element: its properties do not qualify it for any known space on the Periodic Table of Elements. Rather, adamantium is a series of three closely related compounds of iron created through a secret process discovered by metallurgist Dr. Myron MacLain.
Adamantium is created through the mixing of certain chemical resins whose composition is a United States government secret. For eight minutes after the resins are mixed, the adamantium can be molded into a particular shape as long as it is kept at a temperature of 1500 degrees Fahrenheit. After this brief period the process of creating adamantium is completed, and it is cured. The extremely stable molecular structure of the adamantium prevents it from being molded further, even if the temperature ramains high enough to keep it in liquified form. Only a devise called a Molecular Rearranger can alter the form of hardened adamantium.
-The Official handbook of the Marvel Universe; 1983