Editing Cave (section)

===Solutional===
{{Main|Solutional cave}}
'''Solutional caves''' or '''karst caves''' are the most frequently occurring caves. Such caves form in rock that is soluble; most occur in [[limestone]], but they can also form in other rocks including [[chalk]], [[Dolomite (rock)|dolomite]], [[marble]], salt, and [[gypsum]]. Except for [[Salt_cave|salt caves]], solutional caves result when rock is dissolved by natural acid in [[groundwater]] that seeps through [[bedding planes]], [[Fault (geology)|faults]], joints, and comparable features. Over time cracks enlarge to become caves and cave systems.

The largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H<sub>2</sub>CO<sub>3</sub> ([[carbonic acid]]) and naturally occurring [[organic acid]]s. The dissolution process produces a distinctive landform known as ''[[karst]]'', characterized by [[sinkhole]]s and underground drainage. Limestone caves are often adorned with [[calcium carbonate]] formations produced through slow [[Precipitation (chemistry)|precipitation]]. These include [[flowstone]]s, [[stalactite]]s, [[stalagmite]]s, [[helictite]]s, [[soda straw]]s and columns. These secondary mineral deposits in caves are called ''[[speleothem]]s''.

The portions of a solutional cave that are below the [[water table]] or the local level of the groundwater will be flooded.<ref>{{cite web |url=http://www.amazingcaves.com/learn_formed.html |title=Learning about caves; how caves are formed |access-date=September 8, 2009 |author=John Burcham |work=Journey into amazing caves |publisher=Project Underground |url-status=dead |archive-url=https://web.archive.org/web/20090503192150/http://www.amazingcaves.com/learn_formed.html |archive-date=May 3, 2009 }}</ref>

[[Lechuguilla Cave]] in [[New Mexico]] and nearby [[Carlsbad Cavern]] are now believed to be examples of another type of solutional cave. They were formed by H<sub>2</sub>S ([[hydrogen sulfide]]) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with groundwater and forms H<sub>2</sub>SO<sub>4</sub> ([[sulfuric acid]]). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface.