"Money" was intended to be something of value. At some point in ancient history rulers decided gold was that "something of value." I see connections with Alchemy for that choice, be that as it may.
Silver was added when more money was needed than gold was available.
I'm a bit more familiar with the history in my own country (the US), but I am certain there are global similarities and effects.
During our Civil War (1860-65), as a wartime measure, "promises to pay" were issued, and cash (paper currency) money was created to cover those promises. After the war, the gummint began issuing gold and silver backed currency.
In 1913, Congress under Pres Woodrow Wilson passed two significant finance laws; the establishment of the Federal Reserve Central Bank and the graduated Income Tax.
For a brief 2 year period during WWII, our 5 cent "nickels" were made with silver because nickel was needed for the war effort.
In 1964, our "silver" coinage (10 cent and up) were converted to clad nickel over copper, the silver was removed from circulating coins.
In the early 1970s (I want to say 1973 under Pres Nixon) the US removed the gold standard and stopped pegging our currency to precious metals.
I want to say 1981 we stopped making pennies (1 cent) out of copper, they became copper clad zinc (which are the two poles of a simple battery!). This was done because the value of the copper exceeded the value of the coin.
As of 1980, the last I heard the values mentioned; the scrap / intrinsic value of a 25 cent piece was 7 cents, the scrap / intrinsic value of a 1 dollar bill was 1/10 of 1 cent, the scrap / intrinsic value of a 100 dollar bill was 1/10 of 1 cent.
Now, what passes as cash or currency is electronic dots and dashes, thin air with no scrap / intrinsic value. "Wealth" is only on a ledger sheet, a figment of imagination.
And for the record, in China there is no mortgage market for housing. It is cash on the barrelhead. I know because my wife is Chinese, and her family, even here, saves the money and pays for property outright because it is their tradition, it is what they know to do. And incidentally, as of my visit to China in 2005, cost of living for average workaday joes was considerably less than Stateside - I can't help but think that is in large part because of the housing situation. A nice apartment that might cost 250K Stateside *then* could be had for 30-40K in Beijing. And with our gummint currently on a spending spree with borrowed Chinese money, that discrepancy is only going to get worse - much worse.