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The final stage in cave development begins sometime after the water table lowers. This often happens as streams carve deeper valleys into bedrock. Cavities formed earlier when the water table was higher are left high and dry, stranded in the unsaturated zone where air can enter. Once the cave has been drained calcite can begin to deposit, forming a wide variety of dripstone decorations.
The chemical process causing deposition of calcite is the reverse of the process of solution. Water in the unsaturated zone, which dissolved some calcite as it trickled down through the limestone above the cave, is still enriched with carbon dioxide when it reaches the ventilated cave. The carbon dioxide gas escapes from the water (just as it escapes from an opened bottle of soda pop). The acidity of the water is thereby reduced, the calcium bicarbonate cannot remain in solution, and calcite is deposited as dripstone.
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The lighted interior of Mitchell Caverns.
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The decorative dripstone features are called speleothems (from the Greek spelaion for cave and theme for deposit). Electric lighting in Mitchell Caverns transforms the speleothems into eerie, .......When these structures are highlighted by lanterns or electric lights, they transform a cave into a natural wonderland.
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Stalactites. Notice that some of the stalactites have been broken, exposing their hollow interior structure.
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The most familiar speleothems are stalactites and stalagmites. Stalactites hang downward from the ceiling and are formed as drop after drop of water slowly trickles through cracks in the cave roof. As each drop of water hangs from the ceiling, it loses carbon dioxide and deposits a film of calcite. Successive drops add ring below ring, the water dripping through the hollow center of the rings, until a pendant cylinder forms. Tubular or "soda straw" stalactites grow in this way; most are fragile and have the diameter of a drop of water, but some reach a length of perhaps a yard or more. The large cone-shaped stalactites begin as these fragile tubes and then enlarge to cones when enough water accumulates to flow along the outside of the soda straws. Deposition of calcite on the outside of the tubes, most of which are near the ceiling and taper downward, results in the familiar cone shapes.
Stalagmites grow upward from the floor of the cave generally as a result of water dripping from overhanging stalactites. A column forms when a stalactite and a stalagmite grow until they join. A curtain or drapery begins to form on an inclined ceiling when the drops of water trickle along a slope. Gradually a thin sheet of calcite grows downward from the ceiling and hangs in decorative folds like a drape.
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Stalagmites.
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Sheets of calcite that are deposited on the walls or floor by flowing water are called flowstone. Rimstone dams are raised fence-like deposits of calcite on the cave floor that form around pools of water.
Helictites are curious twisted or spiraling cylinders or needles. They apparently develop when water seeps through the ceiling so slowly that slight chemical or physical changes can cause reorientation of the crystal structure of the calcite or gypsum. Cave corals, also formed by slowly seeping water, are small clusters of individual knobs.
Mitchell Caverns has a variety of other types of speleothems...
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 View geologic map of area (large files!)
General information on caves
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