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Spice and Wolf has far too many currency systems to even remember, and while their values are based on gold and silver content, the trust that the traders give to the coin is more important. Ma'at: In "Knossos", those precious metals are the currency that Dani's using, granted by divine power:. Dungeon Keeper Ami: In Ambush, there's mention of "coppers" as a kind of currency, and Keepers' money is represented in gold coins, but a gold coin isn't a sign of being connected to Keepers, so some surface nations use gold coins as well. The Rainsverse: This trope for the Heartland's coins, but without the decimal exchange rate, opting instead for Old British Money with French names: One gold livre is worth twenty silver sous, and one sou is worth twelve copper deniers.
He also alludes to the problems with a fixed exchange rate when he hopes it won't have the same issues as the Latin Monetary Union.
The fixed exchange rate of The Rising of the Shield Hero is justified in The Hero Melromarc Needs and Deserves, where Deathmask deduces it's the result of a monetary union between Melromarc and one or more other countries. Deconstructed in Harry Potter and the Methods of Rationality, where Harry realizes that with a fixed exchange rate of Sickles to Galleons, any enterprising wizard could use the relatively volatile Muggle market for arbitrage. Given how expensive everything has become, silver and copper quickly become worthless. In The Keys Stand Alone: The Soft World, there are gold Swords, silver Shields, and copper Torches. Only hints of the coinage in Ketafa are given, but when the four are given a pouch of money and sent to Baravada, it's mentioned several times that they're toting around worthless silver and copper coins. Averted in the case of Baravada, where the currency is pretty much dime-sized gold coins and gems of widely varying sizes.
With Strings Attached: Played with and subverted in a couple of cases:. There was a period of economic chaos before one pony managed to create a new silver-based currency system, which Equestria continues to use to this day. After Corona, though, use of gold coin is considered blasphemy, and possibly treason. RainbowDoubleDash's Lunaverse: Before Celestia became Corona, Equestria used to use gold for its currency.