Spoilers for Logan ahead.
The seemingly indestructible adamantium plays a big role in the newest Wolverine movie, Logan. Like kryptonite and Superman or vibranium and Captain America, the fictional metal is just another substance that's inextricably tied to a superhero. Here's everything you need to know about it.
It coats the skeleton and claws of both Wolverine and X-23
Both Wolverine and his female clone from the movie, Laura (a.k.a. X-23), have skeletons coated in the hardy metal. Bad guy Colonel William Stryker originally coated Wolverine's skeleton in the material because the mutant already possessed a knack for healing, meaning he could recover from injuries and surgeries without dying. He planned on using Wolverine as a weapon, but Wolverine escaped.
Logan suggests that Laura, too, was put through the excruciating process, as Wolverine watches footage of her on an operation table. This time it was Stryker's son who forced her to undergo the surgery. (Presumably this son is not Stryker's son James from 2003's X2, himself a mutant with mind-control abilities. Either Stryker had another son or, because this movie takes place in the alternate timeline created by Days of Future Past, he had a son—just not a mutant son.)
It's unclear how the metal might change with Laura as she ages and grows.
It's very rare
In the comics, a doctor created adamantium by mixing a bunch of metals together and then falling asleep in his lab. When he woke up, adamantium existed. But he struggled to replicate it because he didn't know the exact ingredients. (Isn't this how all scientific discoveries go? No?) Adamantium went into Captain America's shield, as did vibranium, a strong metal mined from Black Panther's homeland of Wakanda, but both those characters are Disney properties, while the X-Men belong to Fox. (For nerds, Google: Is vibranium stronger than adamantium?) Anyway, adamantium is very rare because it cannot be recreated.
There's comic book precedent for adamantium being Wolverine's downfall
In 2014, Wolverine was killed by being encased in adamantium. No other metal could penetrate the strong material, including Wolverine's own adamantium claws, since they're the same hardness. Could a laser maybe cut through it though? Someone grab Cyclops.
In Logan, adamantium is apparently poisonous
There's been some rumbling about adamantium possibly being poisonous in a few of the comic books, but in Logan the poison in the metal is killing him. Wolverine's body basically heals itself like a regular human body—but much more quickly. Perhaps working overtime to stave off the poison of the metal plus all the bullets is finally getting to him. Wolverine's death at the end of Logan might be attributed to a combination of the poisoning that was eventually going to do him in and all those slashes and bullets in the final scene.
Let's talk about that adamantium bullet
It's unclear whether an adamantium bullet would actually kill Wolverine or the new and improved Wolverine from the movie. Adamantium, being the same hardness as more adamantium, wouldn't damage adamantium. For example, when you see Wolverine fight Sabretooth, their adamantium claws don't damage each other. So while the bullet might penetrate Wolverine's skin, it seems it wouldn't kill him. In fact, in X-Men Origins: Wolverine, Wolverine is shot in the head with an adamantium bullet and, though he loses his memory, he survives.
And Wolverine carries around the bullet in Logan as his getaway ticket, and it eventually destroys (though maybe doesn't kill?) the new Wolverine.