Limonite

Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH₂O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two principal iron ores, the other being hematite, and has been mined for the production of iron since at least 2500 BCE.

Names

Limonite is named from the Greek word for meadow (λειμών), in allusion to its occurrence as bog iron ore in meadows and marshes. In its brown form it is sometimes called brown hematite or brown iron ore. In its bright yellow form it is sometimes called lemon rock or yellow iron ore.

Characteristics

Limonite is relatively dense with a specific gravity varying from 2.7 to 4.3. It varies in colour from a bright lemony yellow to a drab greyish brown. The streak of limonite on an unglazed porcelain plate is always brownish, a character which distinguishes it from hematite with a red streak, or from magnetite with a black streak. The hardness is variable, but generally in the 4 - 5.5 range.