Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved ore minerals. In other cases quartz and iron oxides, limonite, goethite, and jarosite, exist as pseudomorphs replacing the pyrite and primary ore minerals. Frequently gossan appears as a red stain against the background rock and soil due to the abundance of oxidized iron and the gossan may be a topographic positive area due to the abundance of erosion resistant quartz and iron oxides. Weathering is the process of decomposition and/or disintegration of rocks in situ, that is, in place. ... An ore is a mineral deposit containing a metal or other valuable resource in economically viable concentrations. ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... Quartz is the second most abundant mineral in the Earths crust. ... Limonite Limonite Limonite is a ferric hydrate of varying composition, the generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as Limonite often contains a varying amount of oxide compared to hydroxide. ... Goethite is a hydrated iron oxide, HFeO2 or Fe3+O(OH) (known as lepidocrocite). ... Jarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe3(OH)6(SO4)2. ... The mineral pyrite, or iron pyrite, is iron disulfide, FeS2. ... Topography, a term in geography, has come to refer to the lay of the land, or the physiogeographic characteristics of land in terms of elevation, slope, and orientation. ... Look up Erosion in Wiktionary, the free dictionary Severe soil erosion in a wheat field near Washington State University, USA. Eroded paddock, Australia Detail of erosion Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, movement in response to gravity...

In the 19th and early 20th centuries gossans were important guides to buried ore deposits used by prospectors in their quest for metal ores. An experienced prospector could read the clues in the structure of the gossans to determine the type of mineralization likely to be found below the iron cap. A prospector is normally a person who explores an area for natural resources such as minerals, oil, flora or fauna. ...