Stalagmites and stalactites

Stalactites and stalagmites are conical, icicle-like shapes of pure CaCO that form on roofs and floors, respectively, of caverns. These are precipitated from cold groundwater that drips from limestone crevices. 

Figure 7.1 Cave formations are caused when rainwater and carbon dioxide mix and form a weak carbonic acid, which then dissolves the calcium carbonate of limestone beneath the earth, allowing for cave formation. The photo shows stalactites and stalagmites and other formations at Luray Caverns in Virginia.

Stalagmites are cave formations that start on the floor and grow upward. These formations are caused when water that contains dissolved limestone drips from the ceiling of the cave and lands on the same spot. Sometimes, water dripping off of a stalactite will actually form a stalagmite directly below it. Eventually, a column forms when the stalactite and stalagmite meet. This feature can take thousands or even millions of years to form. 

Calcium carbonate is the primary component of seashells, antacids, marble and limestone (e.g. stalactites and stalagmites in caves), blackboard chalk, scale in water pipes, and calcium supplements for people and animals. It is also used to capture S02 gas in fossil fuel burning boilers, thereby helping to prevent acid rain, and as a soil additive to provide pH adjustment and calcium to farmers soil. 

The example of chicken breath was inspired by the article, From chicken breath to the killer lakes of Cameroon uniting seven interesting phenomena with a single chemical underpinning by Ron DeLorenzo, Journal of Chemical Education, 2001, 78(2), 191. The article also discusses boiler scale, the way that carbon dioxide partitions between hzzy drink and the supernatant gases (see p. 165), and stalactites and stalagmites. 

Carbonic acid (HjCO ) is produced by dissolving carbon dioxide in water. When formed under pressure, it is the gas used in carbonated drinks. In nature, it dissolves the limestone in caves, resulting in the formation of stalactites and stalagmites. It is corrosive as are other acids, although it is considered a rather weak acid. 

In addition to limestone, calcium is also found in other rocks, coral, shells, eggshells, bones, teeth, and stalactites and stalagmites. 

If allowed to accumulate, it can lead to blockages in pipes, washing machines, dishwashers, and shower heads. In Nature, we can see more dramatic examples of calcium deposits, such as stalactites and stalagmites. Calcium can also react with other chemicals, such as surfactants, to form insoluble salts that give rise to precipitates ( scum ) deposits. 

Acute scalcntihcdral crystals are sometimes referred to as dogtooth spar. Calcite represents the stable form of calcium carbonate aragonite will go over to calcite at 470 C (K78=F. Calcite is a common constituent of sedimentary rocks, as a vein mineral, and as deposits from hot springs and in eaves as stalactites and stalagmites. 

Stalactites and stalagmites are found in underground caverns in limestone areas. They are formed from the slow decomposition of calcium or magnesium hydrogencarbonates in water (Figure 11.34). 

Figure 11.34 Stalactites and stalagmites have formed over hundreds of thousands of years.

Figure 2-8. Calcium carbonate stalactites and stalagmites in a cave in southern Germany (photographs by the authors).

As introduced above, the interaction between the hydrosphere and the lithosphere frequently results in mass exchange. In this way rocks get dissolved, sediments build-up, stalactites and stalagmites form, materials get transported, and so on. The pH of water and of sediments determines the mobility and solubility of different elements, which may in turn modify the redox potential of the aqueous medium. For example, aluminum, calcium, magnesium, iron, manganese, and other metals become more soluble at low pH if pH increases, their solubility decreases and precipitation occurs. 

These processes occur by precipitation through evaporative concentration of a solute in the aqueous medium until its dissolution capacity is exceeded. Then, a solid is formed and deposited either as a sediment or on a nearby surface. These products are called evaporites. A typical example is the deposition and formation of calcium carbonate stalactites and stalagmites. Evaporation is a major process in arid areas and it influences the chemistry of surface waters. That is why in saline lakes, inland seas, or even in estuaries, evaporites of NaCl or NaCl/KCl and deposits of CaS04 and CaC03 are formed. Here, CaS04 generally precipitates first, and then NaCl. 

Thus, water dripping from the ceiling of a cavern can deposit CaCOs a tiny particle at a time, and over long periods can form stalactites and stalagmites. 

This process and its reverse account for the formation of limestone caves and the stalactites and stalagmites found there. The acidic water (containing carbon dioxide) dissolves the underground limestone deposits, thereby forming a cavern. As the water drips from the ceiling of the cave, the carbon dioxide if ->st... 

What are stalactites and stalagmites How are they formed Calcium chloride. 

There are deeper caves that contain stalactites and stalagmites that could only have formed when the cave was air-filled. Using mass spectrometric UATh dating, Richards et al. (1994) measured sea level low stands down to 50 meters below present sea level. The last extensive thrust of the Wisconsinan ice sheet at about 20 ka is clearly shown. Speleothems recovered from a cave on Andros Island, Bahamas at —45 meters was dated at 139 - 160 ka, showing that sea level must have been at least this low at that time... 

Limestone caverns, shown in Figure 6, form over millions of years. They are made as rainwater, slightly acidified by HsO", gradually dissolves rocks made of calcium carbonate. This reaction is still going today and is slowly enlarging caverns. The reverse reaction also takes place, and solid calcium carbonate is deposited as beautiful stalactites and stalagmites. 

Stalactites and stalagmites in limestone caverns form because of a slight displacement of a reaction from equilibrium. 

Macro- and Micromorphological Characteristics of Flowstones, Stalactites and Stalagmites... 

A technique used for dating ceramics, bricks, sediment layers, burnt flint, lava, and even cave structures like stalactites and stalagmites, based on the fact that some materials, when heated, give off a flash of light. The intensity of the light is used to date the specimen and is proportional to the quantity of radiation to which it has been exposed and the time span since it was heated. The technique is similar to electron spin resonance (ESR). Good for dates between 10,000 and 230,000 years. 

The flowing water becomes saturated with calcium carbonate as carbon dioxide is swept away, the reverse reaction becomes favored, and limestone is deposited in formations whose shapes are governed by the path of the flowing water. Stalactites and stalagmites are examples of similar formations found where water saturated with calcium carbonate drips from the ceiling to the floor of caves over eons. 

Figure 4 Orange and blue lights illuminate this cave. Stalactites and stalagmites form when dissolved solids crystallize and build up over time.

Stalactites and stalagmites in caves are formed from solutions, as shown in Figure 4. First, minerals dissolve in water as it flows through rocks at the top of the cave. This solution of water and dissolved minerals drips from the ceiling of the cave. When drops of the solution evaporate from the roof of the cave, the minerals are left behind. They create the hanging rock formations called stalactites. When drops of the solution fall onto the floor of the cave and evaporate, they form stalagmites. Very often, a stalactite develops downward while a stalagmite develops upward until the two meet. One continuous column of minerals is formed. This process will be discussed later. 

Stalactites and stalagmites form as more rock accumulates. 

Acid in the Environment Carbonic acid plays a key role in the formation of caves and of stalactites and stalagmites. Carbonic acid is formed when carbon dioxide in soil is dissolved in water. When this acidic solution comes in contact with calcium carbonate—or limestone rock—it can dissolve it, eventually carving out a cave in the rock. A similar process occurs when acid rain falls on statues and eats away at the stone, as shown in Figure 16. When this acidic solution drips from the ceiling of the cave, water evaporates and carbon dioxide becomes less soluble, forcing it out of solution. The solution becomes less acidic and the limestone becomes less soluble, causing it to come out of solution. These solids form stalactites and stalagmites. 

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