All about gold: Almost all of the gold on earth arrived during meteorite storms more than two billion years ago. We measure gold purity in carats...24-carat gold in the purest...99%...22 carat is 91%....18 carat is 75%... and 9 carat is 37% gold...usually mixed with copper or silver..i hardens the gold. To date, we have mined almost 180,000 tons of gold. Right now, the US Federal Reserve Bank in New York is the largest single gold storage bank...not Fort Knox....holding approximately 540,000 gold bars, more than 25 percent of the world's gold, much of it owned by foreign governments. As for Ft. Knox, it contains around half of this country's gold reserves. Thirty thousand soldiers and a minefield surround it, predator drones fly surveillance, and 20 ton vault doors protect it. The chemical symbol for gold is AU. It comes from the Latin word aurum meaning 'shining dawn' and named for Aurora, the goddess of the dawn in Roman culture. You can take a single ounce of gold (about 28 grams) and stretch it into a gold thread 5 miles long. In fact, you can make a sheet of gold can thin enough to be transparent. As of 2021, China is the top producer of gold.