Something adamantine is unbreakable. Adamantine is often used in a figurative way. If you’re bound by adamantine chains, get comfy because you’re not breaking free!
When someone is adamant, she won't budge or yield. Anything adamantine is pretty much unbreakable and invulnerable. Adamantine substances also tend to be bright and shiny like diamonds. When used figuratively, adamantine can describe something unbreakable, like the adamantine will of a marathon runner.