If you think about the properties you want in a material that will act as a long-term store of value, Gold and Silver have almost all of them.

They’re not the only materials that have been used as currency; though out civilization, tin, copper, and bronze have all been used as a currency in some form. But Gold and Silver simply do it better.

First of all they are naturally occurring, and while rare they are not too rare. For a physical item to be used as currently you want something that is obtainable in sufficient quantities to be traded and stored, but also not so easily obtained that the market could easily be flooded and relative values would fluctuate too easily for people to put any faith in it.

In addition to striking a good balance between being relatively rare but still obtainable, you need something that can be sourced without complex technology. Both gold and silver and winners here as well; they can be mined and refined by hand with primitive tools. Contrast this to something like Aluminum, which while very inexpensive in the modern world was so difficult to produce pre-electricity that it was far more expensive than even gold on a per-pound basis. In fact, it was so expensive that when he really wanted to show off, Napoleon was said to have served his guests dinner on plates made of aluminum, which was seen as quite the flex of how wealthy he was.

In addition to being relatively easy to dig out of the ground and refine, gold and silver are malleable enough to be worked easily with simple tools. Impure gold (as was common in the pre-industrial days) can also have a melting point as low as 1,500 degrees Fahrenheit, which is obtainable with a coal-fired furnace and bellows that have existed for thousands of years. Contrast this to say, platinum, which has a melting point of over 3,000 degrees and was mostly unworkable until the Industrial Age due to this (and still requires much more specialized equipment).

Gold (and to a lesser extent silver) also has one other very important characteristic that has made it an endearing store of value over the centuries; it doesn’t oxidize or decompose. If you think about it, this is one of the most critical features you want in a store of value; you want to be able to store it for long periods of time (and under not always ideal conditions, such as being buried) and not have to worry about your material changing into some other type of much less valuable material. Copper was frequently used as a currency as far back as the Roman Empire, however copper oxidizes quite readily. If you buried your life’s savings worth of copper in your backyard, you’d come back a couple of years later to find them almost completely corroded away to nothing. Gold, by contrast, is so corrosion resistant that it reacts with basically nothing; in fact, there’s only one type of acid that can actually dissolve gold (and platinum); Nitro-hydrochloride acid, otherwise know as “Aqua Regina” for this unique capability.

TL-DR: Gold/Silver are rare but not too rare, they’re easily to mine, refine and work with simple tools, they don’t rust or corrode or decompose, and they’re pretty.