Such concentrations are usually created by geological events, such as volcanic eruptions and tectonic plate shifts that steer hot metal-bearing fluids into upper, accessible parts of the Earth's crust, erosion, or massive sedimentary movements.

WSJ: Exhausting the Earth's Resources? Not So Fast

Since the 1920s, the way to make a car has been to construct a metal shell bearing all the stresses, based on load-bearing floors, pillars and panels hammered out by huge presses costing millions of dollars.

ECONOMIST: Cars

To the bottom would be lowered waste-bearing metal canisters a foot across and 15 feet long.

FORBES: The Big Dig