g27.    How fast are supplies of mineral being used up?

Future supplies depend on the actual or potential supply, and the rate at which that supply is being used. Depletion time is the time it takes to use a certain portion ­ usually 80% ­ of the reserves of a mineral at a given rate of use. There are two categories of minerals: critical minerals, essential to the economy of a country, and strategic minerals, necessary for national defense.

e19.    What materials can cause water pollution?

e23.    How is soil important to plants?

m17.   What’s happening to the tropical forests?

m22.    How are energy resources used?

m29.    How is oil recovered?

m41.    How can matter affect the environment?

m55.    What are the environmental impacts of using up our mineral resources?

m56.    How can we increase mineral resource supplies?