Goethite

Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide. It found in soil and other low-temperature environments such as sediment.

Goethite well known since ancient times for its use as a pigment (brown ochre). Evidence found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).

Goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore. Goethite’s hardness ranges from 5.0 to 5.5 on the Mohs Scale, and its specific gravity varies from 3.3 to 4.3. The mineral forms prismatic needle-like crystals (“needle ironstone”) but is more typically massive.