Such stains are more common in arid regions. Brown is a common stain which could be caused by a number of factors, including organic compounds. Sphalerite, a zinc sulfide, may create a dull brown stain. The sulfide minerals pyrite and tetrahedrite often give rise to chocolate- brown staining. Gold is sometimes present in such settings.
Manganese oxides create black stains in all climates.
Black stains can also be caused by organic compounds. The prospector must keep in mind that color should not be depended on in the search for ore deposits. But, a colorful area in the midst of drab igneous rocks signals the presence of some sort of mineralization. Such areas attracted the attention of prospectors 150 years ago, so it is not likely that very many deposits have been left undiscovered. Yet, they still deserve to be checked.