Well. Take into account #preciousmetalinflation which believe it or not will be a thing in less than a decade most likely.
Right now there is a finite amount on earth. But not for long. #spacemining will flood the market with gold, platinum and others. That will change the standard.
Of course, the mining companies can do the same as was done with diamonds. They are essentially just as common as quartz, just mined and hidden away to inflate value. #variables