What is fool’s gold?

Fool’s gold is the nickname for iron pyrite, a naturally occurring mineral. It is so called because of its close resemblance to gold, which has deceived many miners prospecting for gold over the ages. Like gold, it is brassy yellow in colour with a brilliant lustre.
A widely occurring substance, this mineral is found under extremely varied conditions. It occurs in large deposits in contact metamorphic rocks and in sedimentary rocks. Sometimes it can be found in quartz crystals and in coal beds.
There are many ways to distinguish fool’s gold (pyrite) from the real gold. Both have a brilliant metallic lustre, but are different tones of yellow.

Also, gold is much softer than pyrite and can be cut, while pyrite cannot be scratched. If struck with a steel hammer, gold will flatten or change shape without breaking, while pyrite will give off sparks. Further, if rubbed with a hard object, gold remains odourless, while pyrite emits a smell like that of rotten eggs. 

An important source of sulphur, pyrite was earlier mined to produce sulphuric acid, an industrial chemical. Currently it is used in car batteries and machinery.