As with the Ithildin (Starmoon) with which they marked their doors, Mirian was wrought from Mithril which they traded with the Dwarves for. The currency would commonly be traded between the races at locations such as the market of Khazad-dûm. To honor the Dwarves, Mirian pieces featured Durin's door on one side and its great forge on the other.
During a livestream, Monolith confirmed that Mirian will be used as a currency in the upcoming game Middle-earth: Shadow of War. Orcs of the marauder tribe would be able to scavenge Mirian for Talion.