A Single Limonite Ore On White Background. Stock Photography

Limonite is an iron ore consisting of a mixture of hydrated ironIII oxide-hydroxides in varying composition. The generic formula is frequently written as FeOOH·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, and has been mined for the production of iron since at least 2500 BCE. One of the first uses was as a pigment. The yellow form produced yellow ochre for which Cyprus was famous, while the darker forms produced more earthy tones. Roasting the limonite changed it partially to hematite, producing red ochres, burnt umbers and siennas.