Dolomite introduction

2. Presented by:
Hammad Ahmad sheikh
BS Hons(4th Prof)

3. • Carbonate rocks
• Minerals Of Carbonate rocks
• What is dolomite?
• Physical properties of dolomite
• Crystal structure
• Formation of Dolomite
• Fabric of Dolomite
• Geochemistry of Dolomite

4. • Identification of Dolomite
• Zoned and unzoned Dolomite
• Dedolomitization
• Uses of dolomite
• Conclusion
• Reference

5. Carbonate Rocks
• Carbonates are sedimentary rocks formed at (or near)
the Earth's surface by precipitation from solution at
surface temperatures.
• The most common carbonate sedimentary rocks are
limestone and dolostone, but also Sodium and
Potassium Carbonates can be found.
• Carbonate rocks are Depositionally most simple
but diagenetically most complex rocks of the
world.

6. Carbonate Minerals
• There are a number of a carbonate minerals which
are formed by combining of one or more ion with
the CO
3
2- ion.
• Some important minerals are given in the table (1.1)
Mineral name Chemical Formula
Calcite
Aragonite
Dolomite
Ankerite
Magnesite
Siderite
CaCO3
CaCO3
CaMg(CO3)2
CaFe(CO3)2
MgCO3
FeCO3
Table 1.1

7. Dolomite
• Dolomite is an carbonate
mineral composed of
calcium magnesium
carbonate CaMg(Co3
-2).
• Dolostone is a termed use
for a sedimentary rock
which is formed from
such a mineral.
Physical Properties of Dolomite
Color
Hardness
Streak
Crystal system
Luster
Tenacity
White,grey to
pink,yellow
3.5 to 4
White
Trigonal
Vitreous to Pearly
brittle
Table No 1.2

8. Crystal Structure
• It is a rhombohedra
carbonate consisting
of alternating layers
of carbonate anions
and the cations.
• In the crystal
structures there is a
Ca and Mg ions
arranged with Co3
-2 . Fig 1 showing the crystal lattice of
dolomite.

9. High
Magnesian
Calcite
Proto
Dolomite
Stochiometric
Dolomite
Formation of Dolomite
• Dolomite is formed by
the replacement of the
calcite ions by the
magnesium ions.
• Depending upon the
ratio of the mg ions in
the crystal lattice they
have different names.
Fig 2 showing the stages of Dolomite
formation.

10. Formation of Dolomite
Fig 3 showing the formation of high ordered dolomite from high-mg calcite.

11. Formation of Dolomite
• In the high-Mg calcite there is a 0-32 mol% of Mg
substitution for Ca.
• In the Protodolomite there is roughly 55-60 Mol%
Cain the lattice with incomplete segregation of Ca
and Mg into separate layers
• In the stoichiometric dolomite has a 50:50 of Ca to
Mg Ratio with near perfect ordering of the Mg ad Ca
in alternate cation layers.

12. Formation of Dolomite
• Anciently Primary dolomite is very rare only forming
in certain lakes and lagoons while most of the
dolomite is from the replacement origin.
Two major considerations in the formation of
dolomite are:
1. The source of the Mg+ ions.
2. The process whereby the dolomitizing fluid is pumped
through the carbonate sediments.

13. Formation of Dolomite
• To study the ancient dolomite five broad categories of
dolomitization models are currently available which are
given below:
1. Evaporative Dolomitization
2. Seepage-reflux Dolomitization
3. Mixing-Zone Dolomitization
4. Burial Dolomitization
5. Seawater Dolomitization
Each involves different type of dolomitizing fluid, mode of flow
and geological settings.

14. Formation of Dolomite
• Evaporative Dolomitization:
o Dolomite is being precipitated within high intertidal
supratidal and sabkhas enviornment.
o Dolomitic that formed in supratidal enviornment are
precipitated from evaporated sea water.
o Early formation of aragonite and gypsum leading to a
higher Mg/Ca ratio of porewater to facilitate the
dolomitization.

15. Formation of Dolomite
• Seepage-reflux Dolomitization:
o This involves the generation of dolomitizing fluids
through evaporation of lagoon water or tidal flat pore
water and then descent of these fluids into underlying
carbonate rocks.
Sea
level
Saline lagoons and sabkhas
Dolomitization
Mg
bearing
fluid

16. Formation of dolomite
• Mixing Zone dolomitization:
o This type of dolomite formed by the mixing of sea
water with the fresh water.
Sea level
Reef
Materoic
vadose
zone
Meteroic
phreatic
zone
Rain
Mixing
zone

17. Formation of Dolomite
• Burial Dolomitization:
o The principal mechanism is the compactional dewatering of
basinal mudrocks and the expulsion of Mg rich fluids into
adjacent shelf edge.
o The transformation of clay minerals with increased burial
and rising temperature suggest that it would liberate Mg
ions along with Fe ion.
o Basinal shales are commonly organic rich and the
diagenesis would contribute to Co3 ions.

18. Formation of Dolomite
• Seawater Dolomitization: itself can also be a source
of Dolomite because it contains the sufficient
amount of Mg ions with little modification if there
is an efficient mechanism for pumping it.

19. Fabric of dolomite
• Nonplaner:
Fabrics with irregular, nonlinear, crystal
boundaries between anhedral crystals are termed
“nonplanar”.Based on the nature of crystal
boundaries there mosaic is termed as Xenotopic.
• Planer:
Fabric showing planer crystal boundaries
with subhedral or euhedral crystal outlines are
termed “Planer-e (Idiotopic)” and “Planer-s
(Hypidiotopic) “respectively.

20. Fabric of Dolomite
• The difference between Planer-e and Planer-s
fabric is of shape of the crystals.
• In planer-e the shape of the crystals are euhedrel.
• In planer-s the shape of he crystals are sub-hedrel

21. Trace Elements
Geochemistry of Dolomite
• Minor and trace constituents are found in natural
calcite,dolomite and aragonite.
• Trace element in dolomite can be present in a similar
manner to the major cations Ca and Mg.
• The trace elements usually studied are Sr,Na,Fe and
Mn.
• Because of trace elements zoning occurs in dolomite.

22. Trace Elements
Geochemistry of Dolomite
• There are two types of zoning
in dolomite:
o Zoned Dolomite
o Unzoned Dolomite
• Zoned dolomite shows
the layering of the
different minerals in the
same crystal that is of
generally Zn and Mn.
Fig showing the zonation in dolomite
crystal

23. Identification of Dolomite
• In the lab it is best identify by staining it with the
Alizarin Red Sulphate Solution.
• Result. — Color of calcite will turn into red-brown,
whereas dolomite will not be affected.
• In the field it gives effervesence with 10% HCL in the
powdered form.

24. Dedolomitization
• Dedolomitization refers to the partial to whole
transformation of former dolomite rocks to a calcian
rich rock.
• The dolomitization can be considered as a kind of
process in which Mg is gradually released.
• The dedolomitization process can be divided in to
two steps
1. Dissolution of Dolomite
2. The precipation of Calcite.

25. Uses of Dolomite
• Dolomite serves as an oil and gas resorvior rock.
• Dolomite is used in the construction industry.
• Dolomite is used in a steel industry.
• Dolomite is used as a source of Magnesia.
• Dolomite serves as the host rock for many lead,zinc
and copper deposits.
• Dolomite used as a pigments,paints.
• Dolomite is used in making of bricks.

26. Conclusions
• Dolomite is a major carbonate mineral.
• Its formation from secondary origin is common.
• Dolomite is generally formed from the replacement
of the Ca ions with the Mg ions.
• In the ancient dolomite the type of its formation can
be of different mechanisms it could not be easily
understood.
• Dolomite can behave as the resorvoir rocks.
• Dolomites have wide uses.