Clacite & Dolomite

Mineralogical and Crystallographic Study of Calcite and Dolomite

1. Calcite & Dolomite -Vishnuraayan. G. 12410034

2. Calcite – Introduction Most common and widespread mineral on or near the Earth’s surface. Only stable form is CaCO 3 Principal constituent of Sedimentary limestones Occurs in carbonate shells as fine precipitates and as clastic materials.

3. Color : Colorless or white , sometimes grey, yellow, blue, red, brown

4. Luster : Vitreous Diaphaneity : Transparent to opaque Streak : White Streak

5. Crystal Shape : Triagonal Cleavage : Rhombohedral Fracture : Conchoidal but rarely visible due to perfect cleavage Hardness : 3.0

6. Specific Gravity : 2.715(if pure) to 2.94 Reaction with HCl powdered + dil. HCl Brisk effervescence proving presence of carbonate group

7. Optical Properties n o = 1.658 n e = 1.486 n o – n e = 0.172 = δ Maximum Birefringence with fourth order or higher colors.

8. Relief : Moderate but large variations are seen Under PPL Under XPL

9. Interference Figures A normal negative uniaxial interference figure is seen. Lamellar Twinning

10. Uses of Calcite Many different uses according to its purity and character. Marbles and crystalline limestones – ornamental stones. Calcium Carbonate is used as a flux in smelting Certain variety of calcium carbonate is used in printing Lime neutralize the natural acids in the soil.

11. Dolomite – Introduction Occurs in extensive beds at many geological horizons Dolomite may be deposited directly from sea water, but most dolomite beds have been formed by the alteration of limestones, the calcite of which is replaced by dolomite. Chemical Composition : (CaMg)(CO 3 ) 2

12. Color : White, yellowish, brown, and sometimes red, green, or black

13. Luster : Vitreous to pearly of crystals; dull of massive varieties. Diaphaneity : Translucent to opaque Streak : White Crystal Shape : Triagonal Presence of Mg reduces the symmetry

14. Cleavage : Rhombohedral Fracture : Conchoidal or Uneven Hardness : 3.5 to 4.0 Specific Gravity : 2.86 Reaction with HCl powdered + dil. HCl Does not rapidly dissolve or effervesce.

15. Optical Properties n o = 1.679 n e = 1.500 n o – n e = 0.179 = δ (nearly equal to that of calcite) Maximum Birefringence with fourth order or higher colors.

16. Relief : Low to moderate or high Interference Figures : A normal negative uniaxial interference figure is seen . Glide Twin lamellae seen on many sections

17. Uses of Dolomite Important Building material. Making of Refractory furnace lining and source of carbon dioxide,

18. How do we differentiate Calcite & Dolomite Dolomite differs from calcite because of the presence of MAGNESIUM. Calcite reacts quickly with acids and produce carbon dioxide bubbles. But dolomite, weakly reacts with acids producing bubbles very slowly . Dolomite is slightly harder and denser than calcite . Calcites form scalenohedrons but dolomites never form scalenohedrons .

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