Dolomite Perspectives on a Perplexing Mineral

particles that first formed as dolomite by direct 
precipitation from seawater or other aqueous solu-
tion. This process creates unlithified dolomite 
sediment. However, later researchers assigned the 
designation of primary to dolomite on the basis of 
its position in the rock fabric.
9
Primary, in this 
case, came to refer to dolomite that has directly 
precipitated above, at or within the sediment, 
while also forming at the same time as that sedi-
ment. Thus, the geochemical term primary takes 
on a stratigraphic context.
>
Smallest to largest. The dolomite label can be applied to the mineral (
left), 
rock (
center) and mountain range (right).
MattV_ORAUT09_Fig_2
4. Shrock RR: “A Classification of Sedimentary Rocks,”
The Journal of Geology 56, no. 2 (March 1948): 118–129.
5. The popularity of this term has waxed and waned over 
the years, mainly because the designation of dolomite 
has historical priority for the rock. However, dolostone 
may once more gain acceptance as researchers seek to 
avoid ambiguity.
6. Machel, reference 1.
7. Machel, reference 1.
8. Machel, reference 1.
9. Rodgers J: “Terminology of Limestones and Related 
Rocks: An Interim Report,” 
Journal of Sedimentary 
Petrology 24, no. 4 (December 1954): 225–234.
10. Warren, reference 2.
11. Sun SQ: “Dolomite Reservoirs: Porosity Evolution and 
Reservoir Characteristics,” 
AAPG Bulletin 79, no. 2 
(February 1995): 186–204.
12. Lucia FJ: “Origin and Petrophysics of Dolostone 
Pore Space,” in Braithwaite CJR, Rizzi G and Darke 
G (eds): 
The Geometry and Petrogenesis of Dolomite 
Hydrocarbon Reservoirs. London: Geological Society, 
Special Publication 235 (2004): 141–155.
Halley RB and Schmoker JW: “High-Porosity Cenozoic 
Carbonate Rocks of South Florida: Progressive Loss
of Porosity with Depth,” 
AAPG Bulletin 67, no. 2 
(February 1983): 191–200.
13. In 1837, Jean-Baptiste Élie de Beaumont used a model 
of mole-for-mole exchange of calcium by magnesium 
to account for vuggy porosity in the dolostones of the 
Tyrolean Alps. Élie de Beaumont J-B: “ L’application du 
calcul à l’hypothèse de la formation par épigenie des 
anhydrites, des gypses, et des dolomies,” 
Bulletin de la 
Société Géologique de France 8 (1837): 174–177.
14. Powers RW: “Arabian Upper Jurassic Carbonate 
Reservoir Rocks,” in Ham WE (ed): 
Classification of 
Carbonate Rocks—A Symposium. Tulsa: The American 
Association of Petroleum Geologists, AAPG Memoir 1 
(1962): 122–192.
This relationship between dolomitization and porosity is 
also reviewed by Lucia, reference 12.
15. Murray RC and Pray LC: “Dolomitization and Limestone 
Diagenesis—An Introduction,” in Pray LC and
Murray RC (eds): 
Dolomitization and Limestone 
Diagenesis: A Symposium. Tulsa: Society of Economic 
Paleontologists and Mineralogists,
 SEPM Special 
Publication 13 (1965): 1–2.
16. Murray and Pray, reference 15.
17. Weyl PK: “Porosity Through Dolomitization: 
Conservation-of-Mass Requirements,” 
Journal of 
Sedimentary Research 30, no. 1 (March 1960): 85–90.
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Autumn 2009
35
Not all precipitates fall into the primary clas-
sification. A different type of precipitate has 
more negative implications in the oil field. This 
dolomite precipitates from aqueous solutions in 
the form of pore-filling cement.
Secondary dolomites are formed through the 
replacement of CaCO
3
by CaMg(CO
3
)
2
. Currently, 
the term replacive, or some variation thereof, 
appears to be eclipsing secondary.
Thus, precipitation is responsible for both 
primary dolomite and pore-filling cement. On the 
other hand, dolomitization forms secondary or 
replacive dolomite. Unfortunately, the latter term 
is frequently used to describe distinctly different 
processes. Many use this term loosely to describe 
either the process in which magnesium ions 
replace calcium ions or settings where precipita-
tion leads to unlithified sediment or pore-filling 
cements. Some experts feel that too much lati-
tude is granted by such usage. To them, dolomiti-
zation should not be applied to dolomite 
cementation or to cases in which hydrothermal 
fluid leads to recrystallization of preexisting 
dolomites. They reserve the term solely for the 
replacement reaction. 
This brief glimpse into the dolomite lexicon 
chronicles attempts by geoscientists to grasp the 
nature of a perplexing mineral. Despite the com-
plexity inherent in dolomite, E&P companies have 
a history of success in exploiting these formations.