This article includes spoilers for episode 4 of The Rings of Power and J.R.R. Tolkiens' works.
The Lord of the Rings: The Rings of Power episode 4 shows us what Durin IV (Owain Arthur) and Disa (Sophia Nomvete) have discovered in the Khazad-dum mine of precious metal mithril. It is highly sought after in Middle-earth for its beauty and durability, and it is as malleable as copper and does not tarnish.
The speed with which the Dwarves mine mithril throughout the Second Age results in a rapid depletion of the ore in the mines. This leads to the Dwarves accidentally releasing a sleeping Balrog, a fiery demon-like creature that destroys Khazad-dum and kills Durin VI.
Durins Bane is a creature found during the Fellowship of the Ring's journey through Moria. Gandalf famously sacrifices himself so that the rest of the group may escape the Balrog, before defeating the creature.
The chainmail shirt worn by Frodo (Elijah Wood) and Bilbo Baggins (Martin Freeman) in The Lord of the Rings: The Fellowship of the Ring and The Hobbit: The Battle of the Five Armies,respectively, is made of the material. The mithril shirt is later handed on to his nephew Frodo by Thorin Oakenshield (Richard Armitage), who then gives it to Frodo. The mithril chainmail is strong
Although Tolkien did not elaborate much on the origins of mithril in the Second Age, we do know that the metal was used to forge at least one of the Rings of Power later. The Galadriels ring, Nenya, is the only ring we know for sure is forged from mithril, but given the lack of background on some other rings, the series might want to have more than one ring forged from this powerful metal.
The Elves are also fond of the glittering quality mithril has, using the alloy ithildin to create elaborate gateways and etching that only exist in starlight or moonlight. Its hard to fault the Dwarves for attempting to mine mithril against Durin IIIs' wishes to proceed more cautiously. After the kingdom's fall, mithril mining ceases, causing it to be nearly impossible to find and growing its value exponentially.
It's difficult to be optimistic about Disa and Durin IV's discovery in The Rings of Power knowing what this implies for their future. Since this is a prequel, and what happens to Khazad-dum is already laid out pretty clearly by Tolkien, there's little the series can do to alter the fate of the Dwarves and their kingdom. However, it'll be interesting to see how the series manages this golden age of wealth and prosperity for the Dwarven kingdom and the spread