Todd Jay Earles, age 11, of W. Des Moines, Iowa, for his question:

How does Bold differ from fool's gold?

These two look enough alike to fool even a wise old prospector. What's more, gold and fool's gold often are found as neighbors in the same rock formations. Chemically the two minerals are not even related. Gold is a metallic element made of atoms of gold. Fool's gold is a compound made of molecules of iron and sulphur. It's more polite names are iron sulphide, iron pyrite and just plain pyrite.

Pure gold is softer and weighs less than pyrite. But it often occurs alloyed with copper or other metals that make it harder. Prospectors used a couple of tests to tell whether they were being fooled. Often they dunked their suspicious nuggets into the laundry tub. The washday chemicals would brighten real gold, but fool's gold would be tarnished. Sometimes samples were heated on a hot stove. This would not harm the gold, but the sizzling pyrite would betray itself by giving off smokey fumes.