1. vibranium isnt equal nor similar to diamond as any other metal in strength and unbreakability. it has actually been broken and shattered in comics.
2. in comics adamantium has bn stated to be closer to a diamond than vibranium in density/durability.
3. aside from that adamantium wasnt created to replace nor replicate vibranium. it was created to remake captain america's shield which is adamantium prime(unique) which of course had vibranuim.
the failed attempts created true adamantium some what close to the properties to cap although not as efficient at kinetic absorption although still present at a lower rate.
based on scarcity alone the value is infinite, or rather, would be limited by the highest bid of the most interested party, much more like origional pieces of art than valued for its utility.
This might drive the piece into the hundreds of millions or low billions, but would not be nearly as valuable as a piece that that could be researched to produce new innovations in the real world. The stipulation you have created really now only measures the anachronistic quality of the device, and is in no way related to its utility, function or ability to affect the modern world.
In this regard, the most valuable item in Marvel would be the one that appeals to the richest person on earth in such a way that they are willing to give all their fortune for it, whatever it might be. and, imho, this is more likely to be a used pair of MJ's panties than a webshooter that can't be patented.
Wolverine's skeleton is officially cited as adding an additional 100lbs to his frame. He weighs 300lbs with Adamantium, and 195lbs without (dated data Marvel has never upgraded since his original built when he first joined the X-Men, his shorter stockier self should be closer to 220... but whatever). The skeleton accounts for about 20% of the bodies weight, so we are looking at a bone skeleton of 39lbs, and an Adamantium skeleton of 144lbs. According to google steel is about 4.5 heavier than bone so a pure steel skeleton would be about 175lbs (plus the 39lbs skeleton if they are fused together like Wolverine's with Adamantium)
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