Earth's largest gold reserves are not kept inside Fort Knox, the United States Bullion Depository. In fact, they are hidden much deeper in the ground than one would expect. More than 99.999% of Earth's stores of gold and other precious metals lie buried under 3,000 km of solid rock, locked away within the Earth's metallic core and far beyond the reaches of humankind. Now, researchers have found traces of the precious metal Ruthenium (Ru) in volcanic rocks on the islands of Hawaii that must ultimately have come from the Earth's core.