Now we come to it. When you bring all of this together, one fact becomes clear: mithril and the Silmarils never cross paths in J. R. R. Tolkien’s original writings. The precious metal is just that, precious, but it doesn’t come from an apocryphal fight with a Balrog that fuses goodness and evil into a light-infused substance.
The Silmarils suffer from unknown fates, and it’s true that Tolkien doesn’t clarify what happens to them after they disappear at the end of the First Age. We know they still exist and that one of them is in the sky, but that’s it. Still, unless there’s an obscure note in Tolkien’s writings somewhere, from where we’re standing, the idea that they’re connected to mithril appears to be completely made up for Amazon Prime’s story.
And yet, there’s an interesting shred of truth in the tale, and it has to do with Elves fading. Elvish immortality is an interesting concept. In fact, the Eldar aren’t immortal, strictly speaking. Their perpetual nature is more like serial longevity that is connected to the existence of Arda (that is, the physical world). Over time, the Elves do fade in some generally undefined capacity.
This concept of “fading” is referred to throughout Tolkien’s writings. Galadriel talks about it in “The Fellowship of the Ring” when she explains that if the Rings of Power are removed from the equation, “then our power is diminished, and Lothlorien will fade, and the tides of Time will sweep it away. We must depart into the West, or dwindle to a rustic folk of dell and cave, slowly to forget and to be forgotten.” Throughout Middle-earth’s history, the Elves are aware of this fading process and what it means for them in the end.