Inside the treasure chest are 3,500 gold pieces, a silver bracelet inlaid with ivory worth another 50 gold, and an amethyst gem worth 100 gold pieces.
That phrase, or others that are practically identical to it, can be found in almost every published Dungeons & Dragons adventure from the game’s first printing almost 40 years ago to the current edition. And there is nothing inherently wrong with that; if describing treasure in that way didn’t work, it wouldn’t have been standard practice for four decades.
The official D&D game has always based its economy on the gold standard, which Wikipedia.com defines as a monetary system in which the standard economic unit of account is a fixed weight of gold. Specifically, it operates on the gold specie standard, through which the monetary unit takes the form of circulating gold coins, as opposed to the gold exchange standard, which allows for other forms of currency (like paper money) to circulate in the place of valuable coins, and which could be exchanged for the coins at the owner’s request.
While this writer is not speaking for the game’s designers, there are good reasons for employing the gold standard in D&D, first among them being player expectations. After being exposed to fairy tales, films and novels of the fantasy genre and pirate stories which feature mountains of gold coins as treasure, someone playing D&D for the first time might be disappointed to find hoards of, for example, mere silver coins, even though virtually all Medieval economies in European history operated on the silver specie standard.