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Sulfate crust
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<p>Sulfate crust is a zone observed in the axial (central) parts of <a href="/facts/Coal_fire/acNeeRD7">burning</a> <a href="/facts/Coal/83kV3qxg">coal</a> dumps and related sites. It is a zone built mainly by anhydrous <a href="/facts/Sulfate/yuWVxsUf">sulfate</a> minerals, such as <a href="/facts/Godovikovite/IPKJFHSH">godovikovite</a> and <a href="/facts/Millosevichite/AIWCdxQQ">millosevichite</a>. The outer zone can easily be hydrated giving rise to minerals like <a href="/facts/Tschermigite/rM79oIl3">tschermigite</a> and <a href="/facts/Alunogen/QGAp5LRW">alunogen</a>. The zone forms due to interaction with hot (even around 600 °C) coal-derived gases (mainly <a href="/facts/Ammonia/MtLtJFtz">NH3</a> and <a href="/facts/Sulfur_trioxide/Ijvm08Lq">SO3</a>) with the "sterile" material (i.e. shales and other rocks serving as the source of Al3+, Fe3+, Ca2+ and other cations) in case of the lack of vents for the gases to escape into the atmosphere. </p>