Reserves: 100,000 tons
Cost: $40 per pound
Critical for: Capacitors for gadgets
In 2000, speculation in the personal-technology market caused a 14-fold spike in prices of tantalum, a rare metal used in capacitors for cellphones and other gadgets. It fueled armed conflict in the Democratic Republic of Congo, which has the best deposits of this element. At some point in the future, manufacturers might be forced to switch to less-efficient aluminum or ceramic capacitors.