The Probert Encyclopaedia of Rocks & Minerals

LIMONITE

Limonite is the hydrated oxide of iron. It never occurs crystallised, but in fibrous, earthy, stalactitic mammillary, porous, or concretionary masses, and often as pseudomorphs formed by the weathering of other minerals such as pyrites or marcasite. It is black or brown in colour and the streak or fine powder is yellow, distinguishing it from haematite. It has a relative hardness of 5. 5. Impure limonite is found in moorland clay soils and also in meadows and bogs in spongy nodules, and is hence known as bog iron ore. In fresh-water lakes it is often deposited as a brownish slime by the action of plants on the ferrous carbonate and in Sweden and Norway this lake ore is periodically collected by raking the bottom of the shallow pools. Earthy
limonite, or limonite mixed with clay is known as yellow ochre.
Research Limonite