Limonite is an amorphous and earthy mineraloid made up of iron oxides and hydroxides of generic formula FeO(OH)·nH2O, Its colour ranges from yellow to orange, ochre and light brown, of ochre, yellow, orange or light brown. The scratch is always ochre or light brown. The main component of limonite is the mineral goethite, though it contains other iron oxides and hydroxides in variable ratios as well. Limonite originates secondarily from the alteration of other iron sources.
Limonite and the coloured clays that contain it, once milled until a fine particle size, are used as a pigment of multiple shades of yellow, orange and ochre since the ancient times. The deep yellow limonite from Cyprus is the most recognized source. Limonite with its multiple shades is still in use as a pigment in luxurious makeup bases and eye shadows in decorative cosmetics. Apart from its use as a pigment, limonite is mined as a source of iron and additional, more valuable associated metals such as nickel and gold.
In Central Catalonia, limonite is found in small amounts mostly as a crust that is laid on by water carrying iron 2+ ions coming from the alteration of the mineral pyrite (FeS2) which is in rock layers with origin in poor in oxygen and rich in organic matter environments. The photos were obtained on the south slope on the mountain of the Cardona castle.
[photos Jordi Badia, identification Josep M. Mata]