Goethite also Romanèchite (20-30mm) from Királyszentistván / Hungary.

The mineral goethite is an iron- and oxygen-containing hydroxide with the chemical formula Fe3+O.OH. However, this mineral should not be confused with limonite, the imperfectly crystallized form of goethite. It has a hardness of 5 to 5.5 on the Mohs hardness scale. The density is 3.3 to 4.3 and the mineral is not radioactive. The mineral was identified in 1806 and is named after the German writer Johann Wolfgang von Goethe who was interested in mineralogy. Goethite is a common iron ore, which occurs all over the world through the weathering of other ferrous minerals such as magnetite and pyrite. In Europe, it occurs in, among others, Alsace-Lorraine (France), Westphalia (Germany) and Bohemia (Czech Republic). It is also used as a clay pigment; Goethite has been found as a pigment in the cave paintings of Lascaux in France. Limonite, the imperfectly crystallized variant of goethite, is a constituent of the umber rock. In 2004, the mineral was also identified on the planet Mars by NASA's "Spirit" robot. This may indicate that water was present on Mars in the past, as goethite is only formed in the presence of water.