Geochemical sampling methods are methods which involve collecting and analyzing various types of geological materials (such as soils, stream sediments and rocks). Historically these methods have been some of the most productive of any methods used in mineral exploration. Sometime mineralization can be extremely difficult to notice, if not impossible to recognize, by simply looking at a sample. Without the use of geochemical sampling methods, many known ore deposits would probably not have been discovered. After discovery, geochemical sampling plays a key role in the description of mineralization. For example, geochemical sampling of soils is often employed to outline the general distribution of mineralization at shallow depths where outcrops of bedrock are minimal or nonexistent.