Ferruginous sandstones on moldavites

Ferruginous sandstones can be found on the surface of moldavites along with stuck grains of surrounding minerals – clays and sands. They can be found even more rarely in partially opened bubbles. They are usually rust-coloured or light brown.

More often a moldavite can be seen with a residue of clay or a mixture of clay and tiny particles of sand. The colour of clay is usually light and can be easily removed from the surface of moldavite. In that case they it is not a ferruginous sandstone.

What is a ferruginous sandstone?

Ferruginous sandstone is a rock originating from sandy sediments where it is created by coagulation in cold waters containing ferric oxyhydroxide. It is a ferruginous sandstone residual rock. Apart from ferrous minerals they also contain fragments of rock and minerals, e.g. silica, carbonate or clay minerals. Iron comes from eroded rock.

Ferruginous sandstones are younger than moldavites. That is why they can be found on their surface.

The Czech names for ferruginous sandstone are ferolit, železivec or ortstein.