Pyrite

Pyrite is an iron sulphide with a characteristic golden metallic lustre, often mistaken for gold by inexperienced prospectors, earning it the nickname «fool's gold». This very common mineral has the chemical formula FeS₂ and is one of the most widespread sulphides in the Earth's crust.

Characteristics

Pyrite displays a characteristic brass-yellow colour with golden reflections and a brilliant metallic lustre. It crystallises in the cubic system, frequently forming perfect cubes, octahedra or pyritohedra with striated faces. It also occurs as compact masses, nodules or stalactitic forms. Hardness is 6–6.5 on the Mohs scale.

Genesis

It forms in several geological environments: in hydrothermal deposits, in sedimentary rocks rich in organic matter, in metamorphic ore bodies and in volcanic fumaroles. Formation typically occurs under low-oxygen conditions, where iron and sulphur can combine stably.

Varieties and curiosities

Historically it was used to produce sulphuric acid and as a source of sulphur. Today it finds application in the production of sulphur dioxide. Particular varieties include radiated pyrite and spherical nodules known as «pyrite dollars».

Importance for collectors

It is highly valued for its perfect cubes and spectacular lustre. Well-crystallised specimens of large dimensions command high prices. Its tendency to oxidise requires careful conservation to preserve the original brilliance.

Italian localities

In Italy it is found in several regions: notable deposits occur on Elba, in southern Sardinia and in the western Alps. Quality crystals come from the mines of Rio Marina on Elba and from the Sardinian deposits of Iglesias and Monteponi.