Gossan is one of the important type of rocks. If we have to define Gossan in general, Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein.. Gossan comes under Metamorphic Rocks. All Metamorphic Rocks have similar properties and formation process. Along with Gossan Definition, know more about the History of Gossan, Etymology of Gossan in next sections.