There are many systems and standards to classificate the speleothems, does not having yet, a universally accepted. The classification proposed by Guimarães (1966), grouped the speleothems in 3 categories, be based on this division in the in good shape of precipitation of minerals, but it is very important to know that each speleothem is the materialize of several factors (chemical, phicical, climatctics, organics), and that this study must be individual and, its classification and grouping become hard.
v Deposition Through Water in Circulation – is the speleothems formed by thedeposition of minerals contained in aqueous solution, which moves in through caves principally by the force of gravity. These speleothems develop through three basic mechanisms: dripping, flow, and the “whirlpool effect” which may occur in currents. They may occur on roof, walls and floors of caves, and they are the commonest forms in caves. Their principal exemples are stalactites, drapery, stalagmites, columns, mud cups, calcite towers, flowstones, horns and rimstone.
ü Deposits of Exudation Water – are speleothems formed in caves from aqueous solutions which, as a result of cappilary effect, circulate slowly and discontinously through pores in the rock or though the intercrystalline spaces of exiting speleothems. A variety of factor (temperature, pressure between the pores in the rock, spaces of the cave, air humidity, ventilation, dripping volume), cause theses solutions to seep from the rock, depositing the calcite or other mineral until then held in saturation. To form this, it is necessary that the water moviment be so slow that no drop is formed at the points of exit, thus the force of gravity do not affect them. It does not occur the sprinkle of drops, but the evaporation of the water and carbonate gas with the preciptation of calcium carbonate (calcite or aragonite), against gravity, taking the most variety forms and sizes, appering exclusively inside the cave. Their principal exemples are: helictites, heligmites, needles, flowers, cotton, angel hair, coralloids, pine trees, leaves, shields or discs, spheres or blisters, orange sticks.
ü Staganant Water Deposits – are speleothems formed in cave from the deposition of minerals in the surface or submerged areas of water. This water may become satured with carbonate by the slow liberation of CO2. These are typically erratic, with no defined orientation, and irregular, generally with numerous projecting crystalline facets; calcite is predominant here. Some exemples: geodes (dog´s teeth, triangles, pyramides, stars), rafts, calcite bubbles, platforms, clubs, corncobs, candlesticks, concretions, pearls, volcanoes.
ü Deposits of Biological Origin – are speleothems formed by the action of animal or vegetable organisms in caves. They may occur in depositional or erosional forms, and at times as a combination of both at same time. Some exemples moonmilk, speleophotothems.
ü Mixed Origin Deposits – the chemical composition and final aspect of some speleothems are related to the simultaneous or sequentional action of more than one mechanism of action. Some exemples: cementing, anemolites, spherical stalactite, cow´s udder, paw of elephant etc).
v Stalactites – these are the commonest of all speleothems, and occur in practically all known limentone caves, and sometimes in caves of other types of rock .
Their genesis could hardly be simpler: the drops of water with mineral in solution comes from fissures in the cave roof, and remains afflixed to the roof for a certain time until the volume builds up sufficiently to overcome surface tension, and the drop falls. During the period, carbonic anhydride (CO2) is liberated into the atmosphere of the cave, the solution becomes supersaturated, and a delicated ring of calcite is preciptated at the pint of contact between drop and roof. Drop by drop, a tubular stalactite, aclled a soda straw grows vercally downward towards the floor.
These straws vary between 2 and 9 mm in diameter, and their walls are approximately 0.5 mm thick; they may in exceptional cases reach a lenght of three metres.
Each crystal is generally deposited in crystallographic continuity with the preceding crystal; this is shown by the parallel cleavage planes which are exposed when a stalactite of this sort is broken open. Monocrystalline stalactites are usually transparent.
The growth rate of such tubular stalactites varies from place to place and from epoch to epoch, but, according to studies carried out in various parts of the world, it is somewhere in the region of 0.3mm per year (Guimarães). Nevertheless, it is a known fact that there is no “average growth rate” for stalactites, and that the notion is merely a point of reference.
Stalactites also grow in diamter: the original tube is normally porous and the water may, by means of interstices and the cleavage planes of the mineral deposited, move to the outside of the stalactite, where it deposits part os the material which it is carrying. This usually takes place when the central canal is blocked by the growth of crystals on the internal walls.
The water thus held back in the central passage may also leak out by way of the pores at the point where stalactite and roof meet; it then runs down the outside surface, depositing thin sheets of calcite which enclose the stalactite itself. The greater deposition on the upper part of the surface gives the stalactite the conical form associated with it by tradition.
formed when a drop of water emerges on an inclined wall or roof. It runs
down the surface, leaving behind a slight trial of CaCO3 which, as the
process goes on, grows vertically until it forms a white, translucent,
undulating sheet of calcite.
v Stalagmites – a drop of water, falling from the roof of a cave or from a stalactite, on reaching the floor precipitates the calcite which it contains in solution. Continual dripping, and deposition of the calcite, gives rise to a speleothem known as a stalagmite, which grows vertically upwards from the floor. It can have several metres high and more than one metre of diameter, it can have shapes like:
v Columns – are the speleothem formed by the union of stalactites and stalagmites.
v Mud Cups – Mud Cups – when dripping occurs on non-compacted soils, or soils of little consistency (deposits of sand or clay on river bancks), it hollows out little orifices in the floor of the cave. As the process goes on, these pits get deeper, and the walls are covered by the precipitation of calcite, while the spray effect caused by the drops, forms an upper margin or lip. When this process of deposition is carried to an extreme, the cup is turned into a stalagmite with a “root”.
v Calcite Towers – are groups of small clay pinnacles covered with calcite. They are formed by a process of differential erosion and mineral deposition similar to that which forms colunites. In the latter, dripping opens isolated orifices in clay deposits,; in the formation of towers, the erosion is caused by a multiplicity of neighbouring drops. The areas between the orifices, untouched by erosion, and areas protected by pebbles which resist the impact of the drops remain as witness to the clay bank in the form of little towers known as fairy chamneys. These chimneys are speleogens rather than speleothems. However, in certain cases these residual towers are covered with calcite from the dripping of saturated solutions – as occurs with mud cups – and the calcified towers are turned into speleothems.
v Flowstones are laminar deposits which cover the walls and floor of a cave; they arise through precipitation of calcite dissolved in the water which runs over these surfaces. They may adopt a wide variety of shapes:
v Horns – these strange and rare formations are to some extent related to stalactites in that they are roof speleothems, cylindrical and hollow, through which water descends into the cave. Here, however, the process of deposition is due not to dripping but to the circulation of a spout of calcite-saturated water which reaches the cave by a regular orifice on the roof. Part of the falling water slides down the inside wall of the rocky conduit and deposits the calcite. On account of ‘whilpool’ action, depositions take place with greater intensity at the ‘mouth’ of the orifice, and consequently CO2 is liberated into the environment. In this fashion a thick ring is formed at the edges of the orifice; as the process goes on, it grows vertically, taking on the shape of a hanging tube similar to a horn. Greater details of such deposits are still necessary.
v Rimstone Dams – are flowstone formationswhich look like small dykes and which hold back, in a series of “ladders”, the water which runs along the floor of a cave. The appearence of the flooded ladders arises from sinuous lamellar walls, generally concave with the current behind them. Rimstone dams are extremely variable in size: they may be only a few millimetres high (microgours), or they may reach several metres, when they form veritable walls. As rimstone dams hold back water in carbonate, they form an important “cradle” for the formation of a variety of other mineral deposits in caves, including “dogtooth” crystals, “cave pearls”, “volcanoes” and “cave rafts”, all of which are decribed in their appropriate place. Their color is usually brown, because of the impurity in the water, but in some cases, principally when small, they can have a specific color as red to orange because the presence of iron, or white when calcite or argonite is present.
v Helictites and Heligmites – are filiform speleothems, beautful and delicate, they are formed exclusively inside the caves and in specific conditions. Their form and size can vary depending on the climate, physical or chemical situation, they rarely exceed a few centimetres in size, but can occasionally reach one metre. They present a central duct with a micro-diameter of 0.008 to 0.5mm, in which circulates over hydrostatic and capillary pressure the water from calcareous rock, being that the outflow volume in these ducts is of the order of 10-8l/sec. When the water leaves the end of the duct, given liberation of CO2, the micro volume of water evaporates without dripping and the calcite precipitates, provocating the growth of the speleothem, in a curved form and ascendant (against gravity). It is called helictite, when it is formed on the roof and wall, and heligmite when it is formed on the floor and over others speleothems. For its form, it can be: filiform, rosary, veriform and branching.
v Aragonit Needles – are magnificent speleothems formed of fine (1 to 2 mm across) and rectilinear crystals, up to 30cm long. They are transparent and grow on decorated walls and on other speleothems, which no predominant orientation.
v Cave Flowers or Anthoides – is a term used to cover a variety of “erratic” speleothems, of aragonite or calcite, with several delicate forms, characterized by a group of tentacles, brachs, filaments or needles radiating from a centre or common axis. They have no central conduit and are formed by a slow deposition of minerals though solutions which move on their outside surface. In simpler forms they can be confused with helictites. Their genesis are very discussed and based in their morphology, three types of flower are characterized:
v Gypsite Flowers – group of striated and twisted crystals, relatively frequent in Brazilian caves, where they fill cracks in the rocks or cover walls with fine and sometimes scintillating crusts of crystals formed by gypsite (calcium sulphate).
v Cave Cotton and Angel Hair – rare speleothem constituted of gypsite that form fine crystals, in a delicate crystalline web which hangs down from the roof of the cave. They are extremely fragile, bright, forming a chumaço fibroso white, similar to a cotton.
v Needles – speleothem formed by fine elongate crystals, individual, usually transparent, and a white or cream coloration, they are rigid and fragile. They can reach the exceptional lenght of up 25cm, accuring in dry caves or passages and made by sulphate, specially gypste, but also by mirabilite, epsomite and selenite.
v Coralloids – speleothem which are composed of groups of nodules or braches of calcite, or some other mineral , The component parts, which may take the shape and the name of rods, corals, cauliflower , popcorn , branches of grapes, or mushrooms, are generally small. Their structure are concentric, having no central duct, their color can vary from yellowish white and dark brown, due to the presence of impurities in the calcite and formed by the exudation of the water on the walls and floors of caves or pores of others speleothems.
v Pine Trees or Mud Firs – they are individual structures which always occur in groups of dozens or hundreds all over the floors of the dams that present water periodically with conical structures with rugose surfaces, rigid and vertical, formed by carbonated firs, firmly cemented the floor. The genesis of these mud firs appears to be ralated to exudation by capillary, generating the decomposition more accentedof calcite.
v Calcite Leaves – formed by exudation in stalagmites, forming ascendant leaves or petals.
v Shields or Discs – are flat circular or semicircular speleothems which project obliquely or at right angles from the walls of a cave. They are only a few centimetres thick but often reach more than 1 metre in diameter.
v Spheres or Blisters – are small spherical white protuberances which occur on the walls of caves, usually in areas otherwise occupied by corals. They differ from the latter in being hollow. They can be composed by gypsite, calcite, chalcedony and opal.
v Orange-sticks – are helictites or aragonite flowers of which the free extremities are wrapped in little white tufts of a porous consistency. They are probably formed by the deposition of magnesium salts ans of the “monnmilk”.
v Calcite Geodes – they appear in the form of crystalline linnings on the submerged surfaces of wells and dams, or of concavities and re0entrances of walls. There are varieties in these speleothems, such as:
v Rafts – they are plane microcrystalline structures, irregular in form, which may reach 25cm in diameter. They can be found floating on the surface of the water, sometimes they are near the edge, becoming permanently attached, simulating a platform. Their origin is from the precipitation of calcite in stagant water with the liberation of CO2 in the level of the water, they might begin this precipitation around “grains”, which float on the surface of the water.
v Calcite Bubbles – are rare speleothems, hollow in structure, usually spherical or hemispherical; they crystallize through the liberation of CO2 on the surface of pools of stagnant water, dams in general, and are supported by floating bubbles of air. They are always less than 1cm in diameter, and about 0.2mm in thckness.
v Platforms – formations similar to rafts, but they are formed from the edge to the centre.
v Clubs, Corncobs and Candlesticks – stalactites positioned only a little way above the surface of carbonate – rich pools may, if there is an increase in the water level, undergo immersion of their tips. In this extremity, stats to occur the crystallization of the dissolved carbonate, it comes to look like a corncob of calcite crystals or the crystallization occurs only at the water-line, thus creating a flat circular structure, this is known as candlestick or the deposition occurs in the spherical form or hemispherical with little “bubbles” giving a aspect of clubs. The colors of these structures are usually dark due to the impurities or firs in the water.
v Concretions – are sedimentary aggregations, usually of calcite, which cover or wrap round small nuclei found on the surface of the soil of a cave. The nucleus may be no more than a grain of sand, a fragment of rock or of another speleothem, a piece of vegetable matter, bone, shell of clams , or of a variety of other substances. We also called face-hardenings the process of deposition of calcium carbonate over the substances that are introduced in the caves, as roots or objects from the half external . The most tipical forms of concretion are the cave pearls, they are concretions of concentric structure which are formed in the interior of rimestone dams or in small wet cavities in the floors and walls of caves , where occurs the dripping and circular moviment of water, which helps in the formation of its spherical form, but it does not is a determinative factor in its formation, since some theories try to explain its genesis. When grouped, they are called pearl nests and their size can go from a few milimetres to up 20cm. But, it is more frequent of 2 or 3cm in radius, and they are basically from calcite. Their growth rate lie between 0.2 and 2.0mm per year.
v Volcanoes – they are found on pools of stagnant water, they have the form of a truncated cone with a concave upper surface like a crater. They are formed by dripping into dams of water saturated with calcium carbonate, and grow vertically like stalagmites from a submerged floor. The drop of water which falls from the roof lands on the surface of the pool, divides, and, through the liberation of CO2, the calcite in precipitation spreads outwards in the form of microcrystals. These precipitates sink, and form a thin circular film on the bottom of the pool. Other drops continue the work, and new layers of calcite follow the first. Although, the diameter of these circular layers gets gradually smaller, bacause of the reduction between the level of the water and the base of acumulation which will slowly raising to the constant deposition. In the centre of the circle, due to water turbulence caused by the impact of the drops, there is no accumulation of calcite, and the layers come to form laminar rings instead of circles, with diameter each time minors, and their hight is limited by the level of the water, thus the “peaks” are generally all on the same level. Frequently in these areas are found rafts and platforms. This speleothem cannot be confused with stalagmites with a superior cavity formed by erosion and corrosion of acid water dripping.
v Moonmilk – is one of the most interesting biothem forms found in caves. It is a paste-like or porous deposit, rather like a white clay. When dry it is powdery and somewhat reminiscent of chalk. It may be composed of a variety of minerals of carbonate nature, including calcite, aragonite, monohydrocalcite, magnesite, hydromagnesite, nesquehonite, huntite etc.
Moonmilk probably originates through the action of micro-organisms found in this type of deposit. These micro-organisms – actinomycetes, algae, and bacteria – have been identified as being responsible for the breakdown of calcite, whence the origin of the components of moonmilk. The mechanism by which this takes place is still not known.
v Salpetre – is formed through the action of bacteria on cave deposits, generally through the association with bat guano. The mineral found in caves is nitrocalcite.
v Speleophotothems – formations identified by Clayton Lino from 1977 on. They have the peculiarity of occuring only in entrance zones and they have their orientation to the luminosity. They appear in the form of small cylinders, rods or elongated cones. Studies about their formation identified them not as depositional forms but as residual forms resulting from the action of algae, which attack the rocky substrate both chemically and physically. Therefore, they may not be formally included among speleothems, but in the so-called “speleogens”.
v Face-hardenings – hibrid speleothem, where the precipitation of calcium carbonate wraps the fragmentos.
v Anemolites – these include stalagmites and helictites of which the direction of growth is clearly conditioned by the circulation of air in entrances or conduits of caves.
v Cow´s Udder – stalactites that are formed after the blockage of the duct by a spherical cover of firs (when they are in inunded areas), occuring the overflow of the carbonated acid water, forming several stalactites of this sphera.
v Tobacco-pipes – stalactites that their lower extremity grow crystals of calcite in a oblique and in an upward direction of growth.