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How to Mine for Gold
Are Olympic Gold Metals Really Made Out of Gold?
Since ancient times, gold has been the element practically synonymous with riches. It's been used as currency throughout history: the earliest known use of gold coins goes back to ancient Egypt, circa 500 BCE. Romans, Egyptians and ancient Indians all used gold forms of currency at different points in history, and as modern nations started to adopt paper currency, they used gold to back its value (though this is no longer practiced).
Of the hundreds of elements on the periodic table, why is gold the one we associate with value? There are several theories, but it most likely has a lot to do with its chemistry. Elements like gases and liquids are not practical to use for currency. Alkaline metals and earths well... try dropping magnesium in water and see what happens. Not so good for a currency. Obviously we can't use gases and liquids as currency. Lead and copper were used as coins in ancient China but they quickly corroded. And lead's highly toxic. Other precious metals, like platinum, are simply too rare to be of any practical currency (plus it takes over 3,000 degrees to melt platinum).
Silver makes for a great currency. It's durable and rare enough to be desired. And gold, in addition to being both malleable and ductile, is very inert. It's one of the least-reactive of any metals, which means it won't corrode when exposed to the elements. Gold doesn't rust or tarnish (Copper turn green after just a few years of being exposed to the elements). Plus--and this is a big one for gold--it's pretty. It's chemical symbol AU is from the Latin aurum, meaning "shining dawn".
Where Does All Earth's Gold Come From? (Science Daily)
"Ultra high precision analyses of some of the oldest rock samples on Earth provides clear evidence that the planet's accessible reserves of precious metals are the result of a bombardment of meteorites more than 200 million years after Earth was formed."
How Much Gold is There in the World? (How Stuff Works)
"It is amazing, but the total amount of gold in the world is a surprisingly small quantity. Here's how you can calculate the total amount that is available."