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Calcium Magnesium Carbonate CaMg(CO3)2
In England, dolomite has become a useful source for the
production of magnesite by reacting calcined dolomite with
sea-water.
Dolomite is a double carbonate rock with composition of Calcium
& Magnesium occurring as arhombohedral crystals, proportion
varying as per mining zone. Dolomite is harder and denser than
the calcite form of calcium carbonate or limestone, and is more
chemically inert and more impervious to acid attack. Chemically
and structurally it is similar to calcite with half the calcium
ions replaced by magnesium. |
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Theoretically, dolomite contains: |
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CaCO3 |
54.35% |
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MgCO3 |
45.65% |
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Analysis for Dolomite: |
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Calcium Oxide |
as CaO |
32.11 |
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Magnesium Oxide |
as MgO |
20.59 |
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Silica |
as SiO2 |
0.25 |
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Alumina |
as Al2O3 |
0.14 |
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Ferric Oxide |
as Fe2O3 |
0.5 |
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Loss on Ignition |
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44.87 |
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PROBABLE COMPOSITION: |
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Calcium Carbonate |
as CaCO3 |
50.94 |
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Magnesium Carbonate |
as MgCO3 |
43.0 |
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In nature, considerable variations in the composition
of dolomite relating to lime and magnesia percentages are found.
When the percentage of CaCO3 increases by 10% or more over the
theoretical composition, the mineral is termed 'calcitic dolomite',
'high-calcium dolomite' or 'lime-dolomite'. With the decrease in
percentage of MgCO3, it is called 'dolomitic limestone'. With the
variations of MgCO3 between 5 to 10%, it is called 'magnesian
limestone', and upto 5% MgCO3 or less it is taken to be limestone
for all purposes in trade and commercial parlance.
Dolomite usually contains impurities, chiefly silica, alumina and
iron oxide. For commercial purposes, the percentage of combined
impurities should not go beyond 7% above which, it becomes
unsuitable for industrial use. It is then used only for road
ballasts, building stones, flooring chips etc. |
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Hardness |
3.5-4 |
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Associated Minerals |
include calcite, sulfide ore minerals,
fluorite, barite, quartz, and occasionally with gold. |
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Chemical/Typical composition |
White. |
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Colour |
Often pink or pinkish and can be
colorless, white, yellow, gray or even brown or black when
iron is present in the crystal |
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Characteristics |
Unlike calcite, effervesces weakly with warm
acid or when first powdered with cold HCl. |
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Luster |
Pearly to vitreous to dull |
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Field Indicators |
Typical pink color, crystal habit, hardness,
slow reaction to acid, density and luster. |
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Applications:
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Paints.
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Glass.
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Ceramics.
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Detergent.
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Foundry Fluxes.
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Chemical Industry.
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Cement.
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