Pyrite from Ambas Aguas, La Rioja, Spain (REF:PYESP10)

The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulphide with the chemical formula FeS2. This mineral's metallic lustre and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. The colour has also led to the nicknames brass, brazzle, and Brazil, primarily used to refer to pyrite found in coal.

Pyrite is the most common of the sulphide minerals. The name pyrite is derived from the Greek (pyritēs), "of fire" or "in fire”, in turn from (pyr), "fire”. 

In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite.

By scholar and scientist Georgius Argricola's time, the term had become a generic term for all of the sulphide minerals.

  

Pyrite is usually found associated with other sulphides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold.

The ancient Incas used Pyrite as mirrors.

It is found all over the world, but important deposits are in Italy, Spain and Peru.