This shiny, yellow mineral can look so like gold is has fooled many prospectors into thinking they have struck it rich. No wonder, then, it is sometime khown as 'fool's gold'. It among the most common of all minerals, found in almost every environment. Indeed, any rock that looks a little rusty probably contains pyrite. It comes in s vast number of forms and varieties, but the most common crystal shapes are cobic and octahedral. One sought-after form is flattened nodules found in chaik, siltstone and shale called 'pyrite suns' or 'pyrite dollars'. The nodules are usually made of thin pyrite crystals radiating from the centre. Pyrite gets its name from the Greek for 'fire' because it can give off sparks when struck - which is why it has been used to light fires since prehistoric times. Although it is rich in iron, it has never been used as an iron ore. In the past, though, it was used as a source of sulphur for making sulphuric acid.