Major Analytes in Limestone Purity test

Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

Limestone is composed principally of calcium carbonate, which when heated at elevated temperatures decomposes to calcium oxide and carbon dioxide.

    CaCO_{3     +         Heat     =}   CaO + CO₂

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The CaCO₃ may account for a composition as high as 98.5% or more in limestone, and when broken down, the value of CaO is 55.19%. Limestone, an impure form of calcium carbonate contains other constituents as impurities in addition to the carbon dioxide present.  These are the calcium and magnesium silicates as well as silicates of iron, alumina, manganese, titanium, sodium and potassium. When the combined value of silicates present is high, the CaO value is correspondingly reduced.

On the other hand, limestone may become dolomitic, that is, in addition to CaCO₃ present; there exists also a large concentration of MgCO₃ in the form of CaCO₃. MgCO₃ in which case the MgO is very large and may reach up to 21% plus. However, the CaO content is much reduced compared to the concentration in a principally CaCO₃ limestone.

The analysis of limestone, irrespective of its nature entails as a primary step, a decomposition reaction with dilute hydrochloric acid to form mainly a solution of calcium chloride from which the various other chemical constituents are derived in a stepwise manner by the application of suitable analytical procedures. The parameters to be determined are: CaO, MgO, (Fe₂O₃, TiO₂, Al₂O₃) or a combination of these as R₂O₃, Acid insoluble component or silica, and Loss on ignition or carbon dioxide (CO₂).

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