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It is commonly known as 'Fools Gold.' It is a mixture of iron and sulphur.
The original name derived from the fact that the substance was used to make sparks to cause fires. That is where the 'pyr' comes in. We still use this old word for fire when we talk about a pyrotechnician - someone who makes things light up. Down through history 'pyr' has become 'fyr.'
Pyrite forms shiny brass yellow cubes. When they are found singly they can be magnificent. They can also be found as beautiful clusters. One reason for it being called 'Fools Gold' is its bright yellow colour. But it is brittle and gold is soft and malleable.
One form of pyrite is the silvery marcasite. Marcasite has the same chemistry (FES2) as pyrite, but it is chemically glued together in a different way. It produces, therefore, different crystal shapes. Marcasite because of its bright silver yellow colour is popular in imitation jewellery. Sadly, both Marcasite and pyrite ultimately react with the air and degenerate into iron oxide - more commonly known as rust, and the sulphur can become a sulphurous acid with sad consequences for many containers.
Surprisingly pyrite has been usually mined for sulphur, rather than iron.
Sulphur was used in the production of sulphuric acid. The rise of the oil industry led to the discovery that hydrogen sulphur was a much better source of sulphur and much cheaper.