<P> Caves can be classified in various other ways as well, including active vs. relict; active caves have water flowing through them, relict caves to not, though water may be retained in them . Types of active caves include inflow caves ("into which a stream sinks"), outflow caves ("from which a stream emerges"), and through caves ("traversed by a stream"). </P> <P> 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, marble, salt, and gypsum . Rock is dissolved by natural acid in groundwater that seeps through bedding planes, faults, joints, and comparable features . Over geological epochs cracks expand to become caves and cave systems . </P> <P> The largest and most abundant solutional caves are located in limestone . Limestone dissolves under the action of rainwater and groundwater charged with H CO (carbonic acid) and naturally occurring organic acids . The dissolution process produces a distinctive landform known as karst, characterized by sinkholes and underground drainage . Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation . These include flowstones, stalactites, stalagmites, helictites, soda straws and columns . These secondary mineral deposits in caves are called speleothems . </P> <P> The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded . </P>

Formed when groundwater mixes with gases and minerals to form a solution that dissolves rock
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