Endangered element: zinc

Sphalerite is the primary ore for zinc.

Why is zinc an important mineral?  By far the most common use of zinc is corrosion resistance, accounting for 80% of the metal's use in the United States.  Steel has two useful properties; it's strong and light-weight.  It also has the disadvantage of being susceptible to rusting.  Stainless steel doesn't rust, but is substantially weaker than other kinds of steel.  Any steel structure that will be exposed to the elements needs to be protected from corrosion.  The solution to this problem is to simply coat the surface of the metal in zinc, which forms a layer of zinc carbonate over time.  This application, however, doesn't threaten future supplies.

Increased demand for zinc will likely be driven by zinc-air cells, useful for creating electric cars.  In 2012, the United States used 26.7 quads—quadrillion BTUs—of energy for transportation, primarily supplied by petroleum.  Zinc-air cells carry about 1600 BTU per kilogram—c.f. 43,000 BTU per kilogram for gasoline.  To replace every conventional car on the road would require 17 billion tonnes of zinc-air cells.  I don't know how much zinc is used to make these batteries, but there are only 1.9 billion tonnes of identified zinc resources in the world.

Can everyone in the world have an electric car?  Probably not—but this answer is too dismissive.  Everyone may not need to own a car in the coming decades.  Greater availability to public transit and autonomous cars could substantially improve the efficiency of transportation.  However, the United States only has 4% of the world population.  Increased demand from the rest of the world—particularly developing nations—could offset any gains from improved efficiency.  The future population of the world is uncertain as well.  Some countries may experience growth in population; others may experience contraction in population.  No single technology will likely be able to replace petroleum burning cars.  Instead, societies will need to rely on a variety of solutions.