Editing Anhydrite (section)

===Salt dome cap rocks===
Massive amounts of anhydrite occur when [[salt dome]]s form a [[caprock]]. Anhydrite is 1–3% of the minerals in salt domes and is generally left as a cap at the top of the salt when the [[halite]] is removed by pore waters. The typical cap rock is a salt, topped by a layer of anhydrite, topped by patches of gypsum, topped by a layer of calcite.<ref>{{cite journal|first=C. W.|last=Walker|title=Origin of Gulf Coast salt-dome cap rock|journal=AAPG Bulletin|date=December 1976|volume=60|issue=12|pages=2162–2166|doi=10.1306/c1ea3aa0-16c9-11d7-8645000102c1865d}}</ref> Interaction of anhydrite with [[hydrocarbon]]s at high temperature in [[oil field]]s can reduce [[sulfate]] ({{chem|SO|4|2–}}) into [[hydrogen sulfide]] (H<sub>2</sub>S) with a concomitant precipitation of [[calcite]].<ref>{{cite journal|title=Origin of 'exotic' minerals in Mississippi salt dome cap rocks: results of reaction-path modeling|journal=Applied Geochemistry|volume=11|issue=5|date=September 1996|pages=667–676|doi=10.1016/S0883-2927(96)00032-7|first1=James A.|last1=Saunders|first2=Robert C.|last2=Thomas|bibcode=1996ApGC...11..667S}}</ref> The process is known as [[thermochemical sulfate reduction]] (TSR).
[[Image:Chickenwire Gypsum anhydrite.jpg|left|thumb|Hand sample of gypsum and anhydrite from diapir caprock showing "chicken wire" texture.]]