Structure/Behavior

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Structure:      

Calcium Carbonate is a salt made up of Ca²⁺ ions and CO₃^2- ions. It forms a rhombohedron crystal because of the attraction that causes the ions to form onto one anther in this specific patter. This crystal is the mineral calcite. The calcite is crystal is generally a rhombohedra because of its cleavage properties. Cleavage of calcite goes in three directions. Cleavage is what causes crystals to angle where the bonding forces are weak and to break into planes. (for information on rhombohedrons visit: http://mineral.galleries.com/minerals/property/crystal.htm#scalahed) that can be altered and combined with other shapes, so there are many different shapes of calcite crystals. There are more than 300 forms of calcite crystals. Calcite crystals also come in many different colors, but usually white or transparent. Pictures below are all calcite crystals; notice the many different shapes and colors:

Pictures Source: http://www.tigerblossom.com/calcite.htm

 Picture Source: http://www.gwydir.demon.co.uk/jo/minerals/calcite.htm 

Another Important property of calcium carbonate or the calcite crystal is its property of double refraction. Double refraction is when the ray of light travels through and is spilt into two different beams, one traveling slowly, one traveling fast. The two different beams are bent at two different angles of refraction. As a result of this property looking through calcite there are two images. Double refraction is useful in the field of optics (see uses page) A picture that illustrates double refraction is below:

Picture Source: http://www.gwydir.demon.co.uk/jo/minerals/calcdref.htm

Chemical Reactions and Tendencies:

            Calcium Carbonate participates a unique reaction with any acid. The uniqueness of the reaction is that it reacts and always produced carbon dioxide with any acid, no matter the strength. This test is used to identify calcium carbonate by geologist or to test construction materials. The equation is:

CaCO₃(s) + Acid (aq) → Ca⁺²(aq) + H₂O (l) + CO₂ (g)

This reaction is also important in understanding the formation of caves since this reactions occurs with calcium carbonate in limestone and later the reverse happens and the calcium carbonate is made into the solid stalactites and stalagmites. This property is also the reason why calcium carbonate is used in antacids (for more info on caves or antacids see uses page).

Calcium Carbonate also decomposes to form lime, CaO, and carbon dioxide. Lime is an important material in the industries of steel, glass, and paper among many others.

CaCO₃(s) → (heat) CaO(s) + CO₂ (g)    

 Here's a model of a Calcium Carbonate Crystal :

  http://earthsci.org/rockmin/atomic/atomic.html