Epikarst, the upper surface of karst, consisting of a network of intersecting fissures and cavities that collect and transport surface water and nutrients underground; epikarst depth can range from a few centimetres to tens of metres.

Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate). The primary source of this calcite is usually marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze (see lysocline for information on calcite dissolution). Secondary calcite may also be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems such as stalagmites and stalactites. A further form is composed of oolites (Oolitic Limestone) and can be recognised by its granular appearance. Limestone makes up approximately 10 percent of the total volume of all sedimentary rocks.

Pure limestones are white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces. Limestone may be crystalline, clastic, granular, or dense, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock. Chert or Flint nodules are common in limestone layers. Bands of limestone emerge from the Earth's surface in often spectacular rocky outcrops and islands. Examples include the Verdon Gorge in France; Malham Cove in North Yorkshire, England; and the Ha Long Bay National Park in Vietnam.

Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution that is supersaturated with chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls.

Karst topography and caves are often formed in areas composed chiefly of limestone.

Uses of limestone

Limestone is quarried for roadbeds, building and landscape construction, and cement manufacture.

Limestone is especially popular in architecture, and many landmarks around the world, especially in North America and Europe, are made primarily of the material. Limestone is readily available and relatively easy to cut into blocks or more elaborate carving. It is also long-lasting and stands up well to exposure. However, it is a very heavy material, making it impractical for tall buildings; it is also quite expensive. Limestone was most popular in the early 20th and late 19th centuries. Train stations, banks and other structures from that era are normally limestone. Limestone is used as a facade on some skyscrapers, but only in thin sheets rather than solid blocks. In North America, most limestone used in construction comes from Indiana.

Though the limestone used for construction is good for humid climates, it is vulnerable to acids, making acid rain a problem when it occurs in places where limestone is used extensively. The acids in the water can wear away the details of statues and other art.
From Wikipedia the free encyclopedia

Speleology is the scientific study of caves and other karst features, their make-up, structure, physical properties, history, life forms, and the processes by which they form (speleogenesis) and change over time (speleomorphology).

Important subdivisions of speleogy are cave hydrology, cave biology, geochemistry of speleothems, cave surveying and mapping.

Speleology is also sometimes applied to the activity of exploring caves. This is more commonly known as caving or spelunking.
From Wikipedia the free encyclopedia

A helictite is a speleothem found in limestone caves that changes its axis from the vertical at one or more stages during its growth. They have a curving or angular form that looks like they had grown in zero gravity.

Helictites are, perhaps, the most delicate and most beautiful of cave formations. They are usually made of calcite, needle-form calcite and aragonite. Forms of helictites have been described in several types: ribbon helictites, saws, rods, butterflies, "hands", curly-fries, and "clumps of worms." Typically the helictite has radial symmetry.

Formation

The growth of helictites is still very enigmatic. Until now there has been no explanation for how they formed, and even now there are only theories.

One theory names the wind in the cave as main reason for the strange look. Drops hanging on a stalactites are blown to one side, so the dripstone grows in that direction. If the wind changes, the direction of growth changes too. However this theory is very problematic, because wind directions change very often. The wind in caves depends on air pressure changes outside, which in turn depend on the weather. Wind caves are known to experience these windy conditions. The wind direction changes as often as the weather conditions outside change. But the dripstones grow very slow, several centimeters in 100 years, meaning the wind direction would have to stay steady for long periods of time, changing for every fragment of a millimeter of growth. A second problem with this theory is that many caves with helictites have no natural entrance where wind could enter.

Another theory explains helictites with capillary forces. If the helictite has a very thin central tube where the water flows like in straws, capillary forces would be able to transport water ignoring gravity. This theory was inspired by some hollow helictites. However, the problem with this theory is that the majority of helictites are definitely not hollow.

A helictite starts its growth as a tiny stalactite. For an unknown reason the chemical composition of the water is slightly altered causing the single crystal structure to change from a cylindrical shape to a conical one. Sometimes each crystal fits into the prior one like an inverted stack of ice cream cones. The direction of the end of the straw may wander, twist like a corkscrew, or the main part may form normally while small helictites pop out of its side like rootlets or fishhooks. In some caves, helictites cluster together and form bushes as large as six feet tall. These bushes grow from the floor of the cave. When helictites are found on cave floors, they are referred to as heligmites, though there is debate as to whether this is a genuine subcategory.

History

The first detailed description of helictites was made in 1665 by Olaus Worm.
From Wikipedia the free encyclopedia

Flowstone is composed of sheetlike deposits of calcite formed where water flows down the walls or along the floors of a cave. Found in "solution", or limestone caves, it is the most common of all cave deposits.

Flowing films of water that move along floors or down positive-sloping walls build up layers of calcium carbonate (calcite), gypsum, or other cave minerals. These minerals are dissolved in the water and are deposited when the water loses its dissolved carbon dioxide, meaning it can no longer hold the minerals in solution. The flowstone forms when thin layers of these deposits build on each other, sometimes becoming rounder as the deposit gets thicker. Sometimes the deposits are so wide and thin they are called "draperies", and many deposits look like static waterfalls.
From Wikipedia the free encyclopedia