Adam Shoemaker, age 12, of Ottawa, Ontario, Canada, for his question:

Where are the world's phosphate deposits?

Phosphates are chemical compounds of phosphorous and oxygen    with usually one or more other elements. Millions of tons of these assorted minerals are used to fertilize our yearly crops. Phosphates come from animal and plant remains as well as mineral deposits. Some of the richest phosphates are manures and other animal waste products, such as guano from bats and birds. Small quantities of bat guano are mined from certain caves. The largest bird guano deposits are along the coast of Peru and its offshore islands.

Most of the world's phosphate deposits are rather soft and usually colorful minerals. The original phosphates in these sedimentary or metamorphic rocks have been mixed with other minerals. The largest deposits are in the United States. Here, 22 million tons are mined annually in Florida, Tennessee, North Carolina and Idaho. Phosphates also are mined in Tunisia, Morrocco and Russia. The United States has wisely set aside 2 1/2 million acres of phosphate rich land for future use