Sulfate crust
Sulfate crust is a zone observed in the axial parts of burning coal dumps and related sites. It is a zone built mainly by anhydrous sulfate minerals, such as godovikovite and millosevichite. The outer zone can easily be hydrated giving rise to minerals like tschermigite and alunogen. The zone forms due to interaction with hot coal-derived gases with the "sterile" material in case of the lack of vents for the gases to escape into the atmosphere.
