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thesis entitled

The Dolomite Growth Mechanism in the
Calcite to Dolomite Transformation

presented by

Lisa Ann Kessels

has been accepted towards fulfillment
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”'93

THE DOLOMITE GROWTH MECHANISM IN THE
CALCITE TO DOLOMITE TRANSFORMATION
By

Lisa Ann Kessels

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geological Sciences

1995

ABSTRACT

THE DOLOMITE GROWTH MECHANISM IN THE
CALCITE TO DOLOMITE TRANSFORMATION

By

Lisa Ann Kessels

Dolomite precipitation at elevated temperatures is limited by the rate of
nucleation and growth in the induction period. At 200° C in Ca-Mg Cl2 solutions,
dolomitization of calcite proceeds by three stages: (1) a period of no stable nucleation;
(2) stable nucleation and slow replacement of the initial products; (3) the rapid
precipitation of dolomite. SEM (Scanning Electron Microscopy) and AFM (Atomic
Force Microscopy) analyses of the reactant surface revealed no products before the first
10 hours of the experiment. Afier 10 hours, Mg-carbonate phases were detected on
calcite. Rapid replacement by dolomite occurs after 12 - 18 hours when only small
amounts of dolomite (1-5%) are detected by XRD. Comparison of the microtopographic
surfaces of products from the slow replacement of the induction period and the later
rapid replacement period indicate the growth mechanism of the products is the same.
Natural dolomite samples from the Seroe Domi Fm, Bonaire, N.A. (Miocene); San
Pedros Island, Belize (Holocene); and the Davis Formation, Missouri (Cambrian),
exhibited the same microtopographic surface features. No growth spirals were observed

on any of the surfaces.

In memory of R. R. Kessels

iii

ACKNOWLEDGMENTS

First, I would like to thank Duncan Sibley for the guidance in completing this
thesis and all the other general advice on life. The second person to whom I am deeply
indebted is Steve Nordeng, an unofficial advisor, whose expertise using the Atomic
Force Microscope was invaluable. I would also like to thank Mike Velbel for his
patience and guidance in the crystallography of carbonates, and Dave Long for letting me
ask him all the last minute questions. Finally, I would like to acknowledge the person

who helped me survive the red tape as a graduate student, Loretta Knutson.

iv

TABLE OF CONTENTS

List of Tables vi
List of Figures vii
Introduction 1
Previous Work 2
Crystal Growth Mechanisms 4
Methods 7
Results 1]
Discussion and Modelling of Results 51
Conclusions 71 3
Implications for Natural Dolomitization 73
Appendix I 77
List of References 86

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

LIST OF TABLES

XRD results and sample list
Model Equations and Constants
Model Transformation Data (n=4)
Model Transformation Data (n=3)

Model Transformation Data (n=2)

vi

6O

77

8O

83

LIST OF FIGURES

Figure 1. Dolomite Transformation Curve

Figure 2. Spiral Growth Model (left) and Birth and Spread Model
(right)

Figure 3. Surface of a sample reacted for 15.0 hours. The sample
represents the late induction period. Arrow points to a cluster
of product crystals (Scale bar = 10 um).

Figure 4. Closeup of Figure 2. Arrow points to a cluster of product
crystals (Scale bar = 10 um).

Figure 5. Surface of a sample reacted for 18.2 hours. The sample
represents the early rapid replacement period (Scale bar = 10 um).

Figure 6. Surface of a sample reacted for 18.2 hours. The sample
represents the early rapid replacement period. Note the increased
number of product crystals on the edges of the calcite surface
(Scale bar = 10 um).

Figure 7. Surface of a sample reacted for 18.2 hours. The sample
exhibits the nucleation of product crystals on previously
precipitated product crystals (Scale bar = 10 um).

Figure 8. Surface of a sample reacted for 94.3 hours. The sample has
completely transformed to dolomite (Scale bar = 10 um).

Figure 9. Microtopographic surface of product crystals from a 15.0
hour sample.

Figure 10. Microtopographic surface of product crystals from an 18.2
hour sample.

Figure 11. Microtopographic surface of product crystals from a 94.3
hour sample.

vii

13

15

19

21

23

26

28

3O

Figure 12. Cross-plot of 15.0 hour sample surface (Figure 9).
Figure 13. Cross-plot of 18.2 hour sample surface (Figure 10).
Figure 14. Cross-plot of 94.3 hour sample surface (Figure 11).

Figure 15. Microtopographic surface of a sample reacted for
9.9 hours.

Figure 16. Closeup of 9.9 hour sample surface (Figure 15).
Figure 17. Closeup of hillocks on 9.9 hour sample (Figure 16).
Figure 18. Block diagram of 9.9 hour sample surface (Figure 15).

Figure 19. Microtopographic surface of a sample from the preliminary
study (Mg/Ca = 1.0) which consists of 89 wt. % dolomite.

Figure 20. Microtopographic surface of a sample from the preliminary
study (Mg/Ca = 1.0) which consists of 97 wt. % dolomite.

Figure 21. Microtopographic surface of dolomite crystals from the
Seroe Domi Fm., Bonaire, NA.

Figure 22. Microtopographic surface of dolomite crystals from
San Pedros, Belize.

Figure 23. Microtopographic surface of dolomite crystals form the
Davis Formation, Missouri.

Figure 24. Model Transformation Curve (n=4)
Figure 25. Model Transformation Curve (n=3)
Figure 26. Model Transformation Curve (n=2)
Figure 27. Actual Data vs. Model Data (n=4)
Figure 28. Actual Data vs. Model Data (n=3)

Figure 29. Actual Data vs. Model Data (n=2)

viii

32

34

36

39

41

43

45

47

49

52

54

56

61

63

65

66

67

INTRODUCTION

Dolomite is the thermodynamically favored carbonate phase in seawater (Land
1985; Hardie 1987). The absence of dolomite in the majority of modern marine
environments has been the subject of investigation for over 50 years. This phenomenon
has been approached through the examination of experimentally-synthesized dolomite
and naturally-occurring dolomites. The synthesis of dolomite in the laboratory has
enabled the study of the reaction curve, chemical catalysts and inhibitors, and the growth
mechanism (Katz and Matthews 1977; Gaines 1980; Baker and Kastner 1981; Sibley and
Bartlett 1987; Sibley et al. 1987; Sibley 1990; Nordeng and Sibley 1994; Sibley et a].
1994). Naturally-occurring dolomites, the end-products of the reaction, have been
petrographically examined to make inferences about the precipitation of dolomite in
nature (Choquette and Steinen 1980; McKenzie 1981; Sibley 1982; Bullen and Sibley
1984; Gregg and Sibley 1984; Saller 1984; Middleburg et a]. 1990; Fouke and Reeder
1992). Both approaches to the problem indicate the reaction initially proceeds slowly,
followed by a period of rapid precipitation (Katz and Matthews 1977; Middleburg et a1.
1990; Sibley et al. 1994).

In this study, three aspects of the process of dolomitization were studied. First,
the initial slow stage of the reaction was studied to characterize the nature of initial

precipitation. Second, the time interval representing the transition from slow to rapid

2

replacement was studied to determine if there is a change in growth mechanism to
account for the rapid increase in products. Finally, the surface topography of natural
dolomites was studied to determine if natural dolomite grows by the same mechanisms
as experimentally-derived dolomite. The natural samples studied are dolomite from the
Seroe Domi Fm., Bonaire, N.A. (Miocene); San Pedros Island, Belize (Holocene); and
the Davis Formation, Missouri (Cambrian). The samples represent a diverse range of
proposed dolomitization models and ages. The Seroe Domi Formation dolomite has
been interpreted to represent dolomitization from mixed waters (Fouke 1994). The
dolomite from Belize is interpreted as dolomitization in the shallow subtidal zone from
seawater (Mazzullo et. al 1994). The Davis Formation dolomite is interpreted as burial

dolomitization (Gregg 1985).
PREVIOUS WORK

The precipitation of most dolomite, CaMg(CO3)2. occurs through a replacement
reaction in which a Ca-Mg carbonate precipitates at the expense of calcium carbonate.
This transformation reaction has been divided into two distinct time intervals (Figure 1).
During the first interval, referred to as the induction period, Ca-Mg carbonate phases
nucleate and replacement of calcite is slow. The second interval is characterized by
rapid replacement and is represented by a sharp change in slope on time-transformation
curves (Sibley et al. 1987; Nordeng and Sibley 1994; Sibley et a]. 1994). Experiments by
Nordeng and Sibley (1994) indicate a series of metastable products precipitate before

stoichiometric dolomite. Their results also indicate there is a progressive increase in the

 

 

 

 

 

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Figure 2. Spiral Growth Model (left) and Birth and Spread Model (right)

 

4

amount of Mg in the series of products. Examination of the reaction curve in previous
studies (Sibley et a]. 1987; Nordeng and Sibley 1994; Sibley et al. 1994) indicates the
induction period is often the longest interval in the entire reaction.

Variables that catalyze and inhibit the reaction exhibit the greatest effect upon the
length of the induction period. Sibley (1990) conducted experiments that demonstrated
the length of the induction period decreased as the Mg/Ca ratio of the solution increased.
Baker and Kastner (1981) found that sulfate in the dolomitizing solution slowed the rate
of transformation. Katz and Matthews (1977) determined that an increase in the
temperature significantly reduced the induction period. Their experiments also showed
that the type of substrate affects the transformation. Aragonite transformed to dolomite
faster than calcite at equal temperatures. Sibley and Bartlet (1987) showed that the
duration of the induction period decreased with higher amounts of reactant surface area.
Their experiments also showed that a very high Mg—calcite (VI-IMC, approximately 35
mole % MgCO3) precipitated even when dolomite seeds were added. Gaines (1980)
found an initial precipitate closer to the composition of dolomite when natural dolomite
seeds were added to the reaction. However, in both of the studies, they report initial
products first detected by XRD. In all of the previous work, however, no degree of

alteration in the reaction conditions has removed the induction period.

CRYSTAL GROWTH MECHANISMS

Crystal formation can be divided into two-dimensional nucleation with planar

growth, and three-dimensional growth (Burton et a]. 1951; Nielsen 1964; Ohara and Reid

5
1973; Christian 1975). Three-dimensional growth, occurring at screw dislocations, is
energetically easier because of the constant supply of energetically favorable sites
provided by the spiral dislocations.

Two—dimensional nucleation models vary between two limiting conditions,
mononuclear two-dimensional grth and polynuclear two-dimensional growth (Ohara
and Reid 1973). In the mononuclear case, nucleation of a phase is considered the rate-
limiting step. Once a phase nucleates, it spreads rapidly across the surface. The
extreme case of polynuclear growth is where there is no lateral growth of the nuclei.
The new phase covers the surface by accretion of nuclei. A model between these two
extremes, referred to as the birth and spread model, involves nucleation and lateral
spread across the surface at a finite rate (Figure 2). In this model, nuclei also develop on
the newly generated surface of the precipitating phase and subsequently spread laterally
across this surface at a finite rate.

The three-dimensional growth model (Burton et al. 1951; Nielsen 1964)
explained why the crystal growth rate from near-equilibrium reactions was greater than
predicted for the two-dimensional model. In the two-dimensional model, if each
nucleus gave rise to only one layer of the new phase of the precipitating crystal, then the
crystal growth observed for reactions at low saturation should not occur because once a
layer is complete the surface energy required to nucleate a new growth unit on a flat layer
would prevent further growth (Nielsen 1964). However, in the three-dimensional model,
spiral growth around a defect has a center from which growth proceeds out laterally as
well as rotating around the center of the defect. The growth proceeding around the

center of the spiral is referred to as the arm of the growth spiral. The center is always

6
higher than the surrounding crystal and acts as the initiation point of the rotating arm
(Figure 2). Thus, the precipitating mineral grows laterally as well as vertically without
the need for a distinct and separate nucleation event for each layer of the precipitating
mineral.

In the laboratory, the growth model for carbonate reactions has been determined
from surface microtopography using the Scanning Force Microscope (SFM), also
referred to as the Atomic Force Microscope (AFM). Dove and Hochella (1992)
observed the in situ formation of clusters ( 6 - 9 nm in height individually, combined
clusters reached 31 nm in height ) that grew laterally on the surface of calcite in contact
with solutions saturated with respect to calcite in a square micron field of view. They
interpreted the observations as the nucleation and lateral growth of calcite on a calcite
substrate similar to the birth and spread model. In their study, they also observe that each
new growth session of calcite is initiated by nucleation and layer growth. Spiral growth
was not observed in their experiments until later in the reaction (2 hours). Gratz, Hillner,
and Hansma (1993) observed sites of calcite initiation that followed a spiral pattern.
These results were interpreted to represent the growth of single-arm and two-armed
growth spirals. The two-armed growth spirals have centers less than 1 micrometer in

size (estimated from their Figures 3a - 31).

METHODS

Laboratory-derived dolomite was synthesized from 0.1 grams of Iceland Spar
calcite (160 - 200 um) placed in 23 ml Teflon-lined bombs with 15 ml of MgCl2 and
CaCl2 solution with a Mg/Ca ratio of 1.2 heated to 200° Celsius. In each bomb, the
solution contained 0.437 grams Mg“ and 0.601 grams Ca2+. The CO," in solution is
from the dissolution of the 0.1 grams calcite. Complete conversion of the Iceland Spar
calcite to dolomite will yield a maximum of 0.092 grams stoichiometric dolomite. A
solution with a Mg/Ca ratio of 1.0 was used during preliminary experiments. At specific
times during the reaction, the bombs were removed, cooled to room temperature, and
analyzed. Each point in the time of the transformation was studied with duplicate bomb
experiments. The contents of each bomb were either kept in contact with the
experimental solution and immediately studied with the fluid cell of the AFM or rinsed
with distilled water and filtered.

Portions of the samples were powdered and X-rayed to determine the
composition and amount of dolomite. An internal CaF2 standard was used to calibrate
the position of the d(104) peaks of calcite and dolomite. The calcite to dolomite ratio
was determined by d( 104) peak height ratios (Lumsden 1979). The composition of the
dolomite was calculated by the position of the d(104) peak and the equation mole %
CaCO3 = 333.33 d(104) - 911.99 (Goldsmith and Graf 1958; Lumsden and Chimahusky
1980). Portions of the sample were also left intact and were prepared for SEM-EDS
analysis. SEM-EDS analysis was used to determine the presence or absence of Mg. The

term Mg-carbonate is used to describe the crystals smaller than the analytic resolution of

8

the instrument ( Sum ). Mg-carbonate crystals smaller than the field of analysis showed
a Mg peak compared to the background calcite which did not show a Mg peak.

Preliminary work utilizing a solution with a Mg/Ca ratio of 1.0 yielded products
with variable mole percent MgCO3. The mole percent MgCO3 increased with time,
similar to the results of Nordeng and Sibley (1994). Two representative samples from
the preliminary study which contain 89% and 97% weight percent dolomite are included
in this study for comparison. These two samples were examined by atomic force
microscopy to determine if the growth mechanism for this particular reaction is affected
by a change in the Mg/Ca ratio. The samples chosen are from the rapid growth and final
phase of the transformation of the preliminary work. Both samples are dolomite with a
composition of Cao.,,Mgo.47CO3.

Samples for AFM analyzes were adhered to a magnetic stub and observed under
the AFM dry cell and wet cell using reactant solution and distilled water as the solution
for the fluid cell. The reactant solution was used to maintain the sample initially as the
surface was characterized. Distilled water was then allowed to flow through the fluid
cell by gravity to determine the relative dissolution rates of different features on the
surface. A record of the particular samples studied with the SEM and AFM is presented
in Table 1. These samples are predominantly from the end of the induction period as
dete'rmined by X-ray analysis. After this time interval of the transformation, the percent
of dolomite product increases rapidly (Table 1). For samples studied with the AFM, the
surfaces of five random grains were investigated in five square micron intervals.

Samples of natural dolomite were prepared for SEM and AFM analyses by

treating their surfaces with dilute acid The dolomite was rinsed three times with 0.5%

 

9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1. XRD results and sample list
time weight % products AFM EEM initial wt. final wt.
2.1 0.0 X 125.823 125.813
2.1 0.0 X 125.918 125.903
4.0 0.0 125.985 125 945
4.0 0.0 126.053 126.003
6.0 0.0 X 125 945 125.91
6.0 0.0 X 126.118 126.11
8.0 0.0 126.139 126.105
8.0 0.0 125.741 125.702
9.9 0.0 X X 125 813 125.763
9.9 0.0 X X 125.919 125.903
12.4 0.0 X 126.071 126.046
12.4 3.6 125.79 125:768
15.0 0.0 X X 125.414 125.369
15.0 0.0 X X 125.889 125.84
15.6 0.0 X X 125.867 125.838
15.6 0.0 X X 124.773 124.725
15.9 2.4 X 125.741 125.702
15.9 0.0 X X 126.139 126.087
16.0 0.0 X X 126.15 126.109
16.0 0.0 X X 126.162 126.136
16.5 0.0 X X 125.911 125.879
16.5 0.0 X X 126.026 126.001
17.0 12.3 X X 126.118 126.08
17.0 26.1 X 125.653 125.629
18.0 33.1 X 126.053 126 003
18.0 44.6 X 125.945 125.91
18.2 0.0 X X 126.038 126.003
18.2 2.6 X X 125.815 125.76
18.2 4.9 X X 126.122 126.109
18.2 8.3 X X 125.744 125.725
18.2 15.5 X X 126.16 126.129
18.2 31.9 X 126.267 126.232
18.2 45.0 X 126.102 126.042
18.2 46.0 X 124.74 124.706
22.4 5.3 X 124.739 124.669
22.4 15.7 X 125.968 125.908
25.0 9.7 X 125.783 125.708
25.0 51.2 X 125.919 125.862
27.0 31.1 X 126.413 126.368
27.0 57.6 X 126.208 126.116
28.0 18.6 X 125.849 125.782
28.0 70.9 X 125.984 125.921
29.0 83.6 125.773 125.705

 

 

 

 

 

 

 

 

Table 1 (cont'd).

 

10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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29.0 82.1 125.909 125.86
30.0 100.0 125.919 125.833
30.0 100.0 124.855 124.793
38.7 64.1 126.225 126.209
38.7 80.4 125.945 125.928
44.0 96.6 125.847 125.77
44.0 95.2 126.148 126.091
64.3 98.6 125.985 125.777
64.3 100.0 125.849 125.709
69.7 100.0 126.358 126.248
69.7 100.0 126.024 125.957
72.8 100.0 125.923 125.808
72.8 100.0 125.881 125.72
80.0 100.0 125.806 125.679
80.0 100.0 124.883 124.759
92.9 96.0 126.005 125.658
92.9 100 0 126.336 125.969
92.9 100.0 126.01 125.948
92.9 100 0 124.912 124.766
94.3 100.0 X X 126.18 126.008
94.3 100.0 X X 124.763 124.61
167.9 100 0 125.929 125 879
167.9 100.0 126.14 126.056

 

 

11

hydrochloric acid in 15 ml portions and filtered using a millipore filter to remove more
soluble phases and salts, and to etch the dolomite slightly to reveal in greater detail the
surface structures. Samples were studied using the dry cell and fluid cell of the AFM.
For image analysis in the fluid cell, distilled water was also allowed to flow across the

surface as described for the synthetic samples.

RESULTS

When the initial solution was 1.2 Mg/Ca, the composition of initial products
formed during the reaction was the same as the final products when the transformation
had gone to completion. The weight percent of products formed relative to the weight
percent of calcite reagent remaining and the initial and final weights of the bombs are
reported in Table 1. The products were a dolomite with an average composition of
Cao_,,Mg0,49CO3 . The composition ranged from 44 - 51 % mole MgCO3 for the 45 out of
66 samples with dolomite detected by XRD. Thus, during the rapid growth interval and
final phases of the transformation, the precipitating phase has the same composition
when the reagant is exposed to fluid with a Mg/Ca ratio of 1.2 at 200° C. In the
preliminary results with an initial solution of 1.0 Mg/Ca, the former scenario was not
the case. The mole percent Mg of the first products detected by X-ray analysis (39 mole
% MgCO3, Sibley 1990) was lower than mole percent Mg of products formed later in the
reaction (47 mole %MgCO3).

SEM analysis verified a dramatic change in the amount of Mg-carbonate and

12

dolomite crystals from the slow replacement stage of the induction period to the rapid
precipitation period as identified by the transformation curve (Figure 1). Figure 3 and 4
are of a sample that was at 200° Celsius for 15.0 hours and contains no detectable
products by XRD analysis (sample from the induction period). Etch pits are present in
the substrate calcite. A cluster of Mg-carbonate rhombs (1 pm in diameter) are also
present on the surface (Figure 3 and 4). Small product crystals ( 0.5 - 2 um in diameter)
occur in small quantities (as few as two crystals have been found on an individual
sample) on the crystal surface of samples with no detectable products by XRD analysis.
The 15 hr sample has fewer crystals on the surface than samples reacted longer (Figure 5,
6, 7, and 8), which is indicative of a lower nucleation rate earlier in the reaction. Figure
5 and 6 are of a sample that was reacted for 18.2 hours and contains 3% dolomite by X-
ray analysis. Figure 5 shows dolomite crystals intergrew and coated the surface of the
calcite substrate. Figure 6 shows the greatest abundance of crystals precipitated at the
edges of the substrate, a feature of the reaction which will be discussed later. Figure 7 is
a sample which reacted for 18.2 hours and contains 5% dolomite. The sample indicates
that after the greater part of the calcite surface was covered with dolomite, dolomite
continued to nucleate on itself as evidenced by the smaller crystals on dolomite
precipitated earlier in the reaction. Figure 8 is of a sample that reacted for 94.3 hours
and contains 100% dolomite by X-ray analysis. Dolomite crystals have completely
replaced the substrate by continued nucleation and growth. The 94.3 hour sample
exhibits crystal intergrowth as well as dolomite nucleation on previously-formed
dolomite crystals. Thus, dolomite continued to nucleate in the final phase of the

transformation.

13

Figure 3. Surface of a sample reacted for 15 .0 hours. The sample represents the late
induction period. Arrow points to a cluster of product crystals (Scale bar =

10pm).

 

Figure 3

15

Figure 4. Closeup of Figure 2. Arrow point to cluster of product crystals (scale bar =
1 um).

 

Figure 4

 

17

Figure 5. Surface of a sample reacted for 18.2 hours. The sample represents the early
rapid replacement period (scale bar = 10pm).

 

 

Figure 5

19

Figure 6. Surface of a sample reacted for 18.2 hours. The sample represents the early
rapid replacement period Note the increased number of product crystals on the
edges of the calcite surface (scale bar = 10m ).

20

 

Figure 6

21

Figure 7. Surface of a sample reacted for 18.2 hours. The sample exhibits the nucleation
of product crystals on previously precipitated product crystals (scale bar = 10pm ).

 

22

 

Figure 7

 

23

Figure 8. Surface of a sample reacted for 94.3 hours. The sample has completely
transformed to dolomite (scale bar = lOum ).

 

24

 

Figure 8

25

The surface of the calcite reagant, as studied by the AFM, is a rough surface with
pronounced etch pits at the near microtopographic scale (1 - 5 um in the x and y
directions) relative to the smoother surfaces of the precipitated dolomite. The calcite
dissolution front did not have a rhombic outline whereas crystals of the product did have
a rhombic outline. However, the steps on those product crystals were irregular, abruptly
ending near the edge of the rhomb. Figure 9 is a microtopographic image of the 15.0
hour sample during the slow replacement stage, Figure 10 is the 18.2 hour sample and
Figure 11 is the 94.3 hour sample. Figure 9 and Figure 10 show concentric growth layers
on the dolomite. There are more centers of growth on the 18.2 hour sample than the 15 .0
hour sample, indicating an accelerated rate of nucleation on the former. The sample of
dolomite from the final phase of the reaction (94.3 hours) also has circular growth
layers on the surface of the dolomite (Figure 11). No growth spirals were observed on
any of the samples. Thus, the change from slow to rapid replacement during this time
interval on the transformation curve is not the result of a change in growth mechanism
from layer growth to spiral growth. Figures 12 and 13 are cross-plots of the 15.0 hour
and 18.2 hour samples. Steps on the surface are interpreted as growth layers on the
forming crystal. These layers consist of growth units which are multiples of the d-
spacing parallel to the d(104), or 2.886 angstroms (Goldsmith and Graf 1958; Lumsden
and Chimahusky 1980) for ideal dolomite (CaomMgojoCOQ. The height of individual
steps on these samples range from 4.4 to 17.6 angstroms. The steps are interpreted as
multiple growth units where a single growth unit is the unit cell. The height of the
individual steps on the 94.3 hour sample range from 15.6 to 24.5 angstroms (Figure 14).

These steps are also interpreted as multiple growth units.

26

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38

A sample reacted for 9.9 hours contained no detectable dolomite or other
products as determined by X-ray analysis. AFM analysis of the precipitate on the
reactant surface shows the same microtopographic surface structures (Figure 15 - 18) as
seen in the previous samples. When distilled water was drawn across the surface by
gravity, the individual layers on the surface of the substrate calcite retreated, but layers
on the precipitate did not retreat within the two hour time flame of the fluid cell
experiment. Thus, the precipitate is a Ca-Mg carbonate of unknown composition Early
carbonate phases in similar experiments are Ca-rich dolomites and very high Mg-calcites
(Sibley et a1. 1994).

Examination of samples from the onset of nucleation in the induction period
(Figures 15 -18), the slow growth stage in the induction period (Figure 9 and 12), the
beginning of the rapid replacement period (Figure 10 and 13), and the end of the reaction
(Figure 11 and 14) all exhibit the same microtopographic surface features. Hillocks on
the surface consist of concentric layers which form terraces of irregular polygons.
Smaller hillocks comprised of concentric layers are randomly located on broad terraces
forming the larger hillocks. A hillock is interpreted as the result of the formation of
nuclei and lateral growth similar to the birth and spread model, or nucleation and two-
dimensional lateral growth model (Burton et a]. 1951; Ohara and Reid 1973; Sunagawa
1984,1986). Thus, the entire reaction is characterized by the birth and spread model.

The surfaces of the two preliminary samples from a solution with a Mg/Ca ratio
of 1.0 also show concentric layers indicative of nucleation and two-dimensional growth
(Figure 19 - 20). Both samples represent the rapid replacement period. Thus, a change

in the Mg/Ca ratio from 1.0 to 1.2 does not change the growth mechanism from layer

39

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51

growth to spiral grth at the transition from the induction period to the rapid
replacement period.

The microtopographic surfaces of natural dolomite samples from the Seroe Domi
Fm., Bonaire, N.A. (Sibley 1980); San Pedros, Belize; and the Davis Formation, Missouri
are also characterized by multiple hillocks and steps with irregular boundaries. Figure
21 is the microtopographic surface structure picture of Pliocene dolomite from the Seroe
Domi Fm., Bonaire, N.A. (Sibley 1980). The surface shows concentric growth layers
consistent with the birth and spread model. Figure 22 and 23 are the microtopographic
surface structure pictures of dolomite crystals from San Pedros, Belize and the Davis
Formation, Missouri. Both surfaces exhibit concentric growth layers and are also
consistent with the birth and spread model. The height of individual steps from all three
natural samples fell in the range of 5.0 - 32.1 angstroms, or presumably grth layers
consisting of multiple growth units. Thus, the examined natural dolomites have surface

structures consistent with the experimental surface structures and growth mechanisms.
DISCUSSION AND MODELLING OF RESULTS

Surface structure microtopographs indicate the Ca-Mg carbonate phases grow by
a birth and spread mechanism during and after the induction period Nucleation occurs
on the calcite as well as on earlier formed Ca-Mg carbonate precipitates. SEM results
indicate the dominate face is the (IO—l4) face. Thus, microtopographs represent the
(1074) face. Growth spirals have been found with the TEM on the (roil) face of early

natural crystals with the aide of cathodltuninesence (F ouke and Reeder 1992). However,

52

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58

in that study screw dislocations were not observed on the (1014) face.

In modelling the grth of dolomites and high Mg-calcites, previous researchers
have determined from modified Arrhenius plots that aqueous diffusion is not the rate-
limiting step (Kunzler and Goodell 1970; Katz and Matthews 1977). Thus, a surface-
limited approach to the precipitation kinetics of dolomitization was utilized Dolomite
preferentially precipitates at the edges and comers of calcite (Figure 6), generally thought
as energetically more difficult precipitation sites, but presumably areas of higher
carbonate ion concentration due to enhanced dissolution of calcite at edges and comers.
However, Ca-Mg carbonate precipitation also occurred at the center of calcite faces
along lines parallel to the crystal edge. A possible reason for the observation of
precipitate concentrated at corners and edges of the calcite and generally areas of higher
dissolution of calcite, is the fact these areas would have a high concentration of steps.
The inside edge of a step would offer another source of bonding and reduce the surface
energy of the new nuclei. However, since the calcite is highly rounded and etched almost
immediately after the reaction begins and well before the precipitation of Ca-Mg
carbonate phases begin, the availability of these preferential sites is not the rate-limiting
step for the growth of Ca-Mg carbonate. The rate-limiting step for the dissolution of
calcite for these particular reaction conditions is inconclusive from SEM results.

The transition from the induction period to the rapid replacement period is not a
result of a change in growth mechanism nor a change in the surface of the dissolving
substrate calcite. Thus, the two main factors left which can accommodate this transition

are the growth rate and the nucleation rate. Since the number of new crystals on a given

59

surface was observed to increase with reaction time, the nucleation rate is increasing
with reaction time. Factors affecting the nucleation rate include the type of substrate
available which varies in this reaction from a calcium carbonate to stoichiometric
dolomite. A substrate closer to the composition of stoichiometric dolomite will be an
energetically easier site for nucleation. Thus, the development of surface area composed
of a mineral of composition close to stoichiometric dolomite, increases the nucleation
rate. The precipitation of mineral of this composition will propagate its own
precipitation by continually providing new substrate and enhances the reaction rate as
demonstrated by the following model.

The transformation data (Table 1) was modelled with the Avrami isothermal
time-transformation curves (Avrami 1939; Christian 1975; Carlson 1983; Sibley 1990).
A growth rate of 1.1 X 10‘8 cm/sec was used as determined previously for the
transformation of calcite to dolomite (Sibley 1990). The nucleation rate, nuclei/cm3sec
(see Appendix I ), was raised to correspond with the increasing number of product
crystals at longer reaction times as observed by SEM analysis.

The modelled volume of products was calculated fi’om the following

equation:

V = 1 - exp (-kt") (Avrami 1939; Christian 1975)

where n is the exponential factor of time and k is the product of a shape factor, the
growth rate cubed, and the nucleation rate. For equations and terms for each of the three

models see Table 2. Figure 24 is a plot of the raw data and the amount of theoretical

 

 

 

 

 

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Model Transformation Curve (n=4)

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62

product calculated from the model with n=4. Figure 25 and Figure 26 are the same plots
of raw data and modelled data with n=3 and n=2 respectively. The power n to which
time, t, is raised, has been correlated to nucleation and growth mechanisms (Avrami
1939; Christian 1975; Carlson 1983). A value of 11 between 2 and 3 correlates to the
dominance of lateral growth away from the nuclei on the surface, and a value between 3
and 4 correlates to a model where nucleation is not superseded by lateral growth, or,
essentially continuous growth in three dimensions. The latter is represented by two cases
(Avrami 1939; Christian 1975). The first case is a spiral growth mechanism where
grth occurs in all three dimensions. The second is the case of birth and spread where
the rate of nucleation is roughly equivalent to the rate of lateral growth. Avrami (1939)
and Christian (1975) both discuss the case where there are a very limited number of
nucleation sites, or germ nuclei. However, in this experiment, there are multiple phases
precipitating. Each phase will have nucleation sites available. As noted earlier in the
discussion of the SEM data, Ca-Mg carbonate phases precipitated on previously
precipitated Ca-Mg carbonate phases and the calcite substrate. Figure 27, 28, and 29 are
the respective best linear fit plots of the actual data versus the theoretical data as
calculated from each model. Figure 28, corresponding to a model with n=3, yields the
best results with an r-squared value of 0.896. However, a model with n=3 requires a
higher nucleation rate to fit the data than a model with n=4 (see Appendix I). The model
with n=4 yields an r-squared value of 0.874. Thus, the data fit a model of n=3 and n=4,
but not a model of n=2 which represents planar growth.

In modelling the nucleation rate, or the number of nuclei on the surface at a

specific point in time, nucleation is broken down into its representative physical

 

 

 

 

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68

components:

N* = N exp (-6G*/k.,T) (Nielsen 1964; Steefel and Van Cappellen 1990)

where N“ is the surface density of critical nuclei at a particular point in time (simply N in
the Avrami models), N (in this equation) is the density of units of the precipitating phase
in the adsorption layer available to accumulate and form a critical-sized radius, BG“ is
the [ice energy required for a critical-sized nucleus to form, IQ, is the Boltzmann's
constant, and T is temperature. A critical-sized nucleus is a stable nucleus that is adding
more molecules of the precipitating mineral than molecules that are leaving the surface.
Assuming the reaction is surface limited, N should be a constant near infinity relative to
N“, or the units of the precipitating phase in the adsorption layer should be much larger
than the units of the precipitating phase actually on the surface forming a critical sized
nucleus (Nielsen 1964; Steefel and Van Cappellen 1990; Nordeng and Sibley 1994).
Since all the other terms can be considered as constants in this experiment, N“ varies
only with 6G“. The free energy required to form a critical size nucleus can be defined as

follows:

SG" = it v3 o3 / 3 (Kb T ln Q )2 (Nielsen 1964; Steefel and Van Cappellen

1990; Nordeng and Sibley 1994)

where Q is the saturation state, v is the molar volume, and o is the surface free energy

69

term. Thus, 5 G“ varies with saturation, molar volume, and the surface free energy term.
The saturation state of the interval of the transformation curve of interest, the induction
period and the transition period from slow replacement to rapid replacement, is
approximately constant because the amount of product formed is too small to change the
solution composition (Sibley 1990). Thus, 5G*, and indirectly N‘, varies only with the
molar volume and the surface free energy term. A smaller molar volume requires a
smaller activation energy. From the previous equations, as SG“ decreases, N“, the
number of critical nuclei, increases. Thus, as more Mg-rich phases (Nordeng and Sibley
1994) with smaller molar volumes are precipitated, the number of nuclei able to
precipitate on the newly generated surface should increase. Since the products detected
by XRD analysis have the same molar composition, the molar volume and surface free
energy term associated with the precipitate during the rapid growth and final phase of the
transformation should be constant and should not change N". However, later in the
transformation, the saturation state will decrease, decreasing N". Thus, an increase in
the Mg content of each new precipitate enhances the nucleation rate because the new
crystals serve as a nucleation site with a lower surface free energy for Ca-Mg carbonates.
The fact that the observations of the final products does not support a decrease in the
nucleation rate indicates the decrease in the Mg/Ca ratio from 1.2 to 1.13, a 5.8%
decrease in the molar ratio, does not stop dolomite nucleation. The lack of a change in
dolomite nucleation is likely due to the large amount of solution relative to the reagant.

As demonstrated earlier, an increase in nucleation up to the end of the induction

period fits the curve of the raw data (Figure 1). Since the end of the induction period

70

also corresponds to the onset of precipitation of dolomite with the final composition for
this experiment, the rate-limiting step is the nucleation and slow replacement of each
separate phase of the different Mg-carbonate products as the Mg content increases up to
the end of the induction period. Researchers (Katz and Matthews 1977; Mucci and
Morse 1983) have shown calcium carbonate with a composition less than 35 mole % Mg
(composition of first metastable precursor detected in experimental dolomitization) and
greater than 21 mole % Mg (Mg/Ca ratios up to 10.3 were required for Mg incorporation
into calcite to obtain high concentrations) are difficult to form and usually do not
precipitate at all. Thus, if the first phase contains 35 mole % Mg, it would be
energetically difficult to nucleate on the reagent, Iceland Spar calcite, as discussed
previously. This energetic barrier would result in the long period with no stable
nucleation.

Sibley et a]. (1987) suggested thermodynamically-favorable environments such as
seawater in contact with calcium carbonate, where no detectable dolomite is forming,
represent the induction period. However, they did not determine when, in the induction
period, stable nucleation first occurs. This study demonstrates that there is not only slow
replacement by Ca-Mg carbonate phases in the induction period, but an initial time
interval in which no stable nucleation occurs. Based on the results of this study we
expect to find some carbonate sediments in contact with seawater in which: 1) no
dolomite nuclei have formed, 2) dolomite nuclei have formed but have grown too slowly
to be detectable by XRD analysis, and 3) detectable amounts of dolomite are present. To
date, no studies have been done to test statements 1 and 2.

The study also verifies that the mechanism by which dolomite precipitates for the

71

observed recent and ancient dolomite is the same as the growth mechanism for the
experimentally-derived dolomite. Although the natural samples were rinsed with a 0.5%
HCl, this is not believed to have greatly affected the surface because of the slow rate of
dissolution of dolomite (Busenburg and Plummer 1982). However, it is likely the Seroe
Domi and Davis formation dolomites have undergone some dissolution after dolomite
precipitation in their natural environments. Dissolution of crystal surfaces can expose
grth layers. Therefore, it is likely the hillocks observed on these natural dolomites
have been exposed to dissolution. Given all the dissimilarities between the three natural
dolomites and the natural versus laboratory conditions, the results suggest that the birth

and spread mechanisms may be very common.

CONCLUSIONS

A rhombic phase which dissolves slower than calcite precipitated before
detectable amounts of product can be verified by X-ray analysis. The surface
microtopographic structure of the Ca-Mg carbonate precipitated during slow replacement
and the dolomite precipitated during the rapid growth and final phases of the
transformation are the same and both indicate grth similar to the Birth and Spread
Model (Burton et al. 1951; Ohara and Reid 1973; Sunagawa 1984, 1986). A slight
decrease in saturation from a Mg/Ca ratio of 1.2 to 1.0 does not affect the surface and
grth mechanism interpretations. Naturally occurring dolomite shows a structure
indicative of the same grth mechanism as the experimentally-derived dolomite.

From the Avrami time-transformation models and raw data, the number of nuclei

72

increase as the Mg content of each new precipitate increases towards stoichiometric
dolomite. AFM analyses show a period of ten hours before any stable nucleation occurs
indicating the first phase is the most difficult to nucleate.

The calcite to dolomite transformation has been characterized by the nature of the
induction period and the rapid replacement period. In this study, the following is
concluded:

I) The induction period consists of two stages. The first stage is characterized by

no stable nucleation. The second stage is characterized by the nucleation and

slow replacement of Ca-Mg carbonate phases.

2) The transition from the induction period to the rapid replacement period is not

the result of a change in growth mechanism.

3) Precipitate from the induction period and the rapid replacement period, as

well as the final products, have microtopographic surfaces interpreted as growth

by a mechanism similar to the Birth and Spread Model.

4) Samples of naturally-forming dolomites exhibit the same microtopographic

features as the experimentally-derived dolomite and consequently, are interpreted

to grow by the same mechanism.

Thus, the lack of dolomite in thermodynamically-favorable environments is
interpreted as the result of a long induction period in which little to no precipitate forms.
The length of the induction period in natural environments will vary considerably due to
fluctuation in conditions, such as saturation state, temperature, and available substrate,
since the length of time in which favorable conditions persist will greatly affect the

induction period. Furthermore, the history of the mineralizing environment determines

73

whether dolomite will form.

IMPLICATIONS FOR NATURAL DOLOMITIZATION

This study of the growth mechanism by which dolomite precipitates demonstrates
the applicability of experimental high-temperature dolomite studies to dolomite forming
in natural environments. The series of studies (Land 1967; Gaines 1974; Katz and
Matthews 1977; Gaines 1980; Baker and Kastner 1981; Greg 1983; Bullen and Sibley
1984; Sibley and Bartlett 1987; Morrow and Rickets 1988; Sibley 1990; Zempolich and
Baker 1993; Nordeng and Sibley 1994; Sibley et al. 1994) including this study, all of
which involved dolomitization of calcium carbonate, have been based on the assumption
that experimentally-derived dolomite and naturally-occurring dolomite grow by the same
mechanism. This study provides direct evidence for similar microtopography, and
subsequently similar growth mechanisms, between natural and experimental samples
despite the stark differences between laboratory synthesis and natural precipitation.

The Atomic Force Microscopy analyses of experimentally-derived and natural
sample surfaces provide three new insights into the process of dolomitization: 1) the
grth mechanism of three different natural dolomites and the experimentally-derived
dolomite in this study is the same, 2) there is no evidence for a change in growth
mechanism during the transition from the induction period to the rapid replacement
period, and 3) characterization of the early stages of nucleation show there is a lack of
stable product formed during approximately the fust half of the induction period. This

allows the kinetic results from previous studies to be applied with greater confidence to

74
events occurring in natural dolomite environments. While this study does not preclude
the existence of metastable phases during the beginning of the induction period, it
demonstrates there is a hiatus after mineral-solution contact and before the formation of
stable nuclei of Ca-Mg carbonates which dissolve slower than calcite.

Observations of natural dolomites which support the inferences made from
experimental modelling range from the scale of a thin section to the outcrop. In nature,
fine-grained calcium carbonate is preferentially dolomitized over coarse-grained calcium
carbonate (Murray and Lucia 1967). Experimental studies show an increase in the rate of
dolomitization with a decrease in calcium carbonate reactant size (Bartlett 1984).
Cathodolurninescence and light microscopy of natural dolomite crystals reveal inclusions
and a mottled appearance at the center of the crystals (Sibley et al. 1994). This is
consistent with observations of dolomite precipitate coating the surface of the calcite
reactant and engulfing the partially dissolved calcite reactant. Similar observations were
made in studies where VHMC precipitated at the expense of calcite and the VHMC was
later replaced by stoichiometric dolomite (Sibley et al. 1994). The textures of
experimentally-derived dolomite and natural dolomites are also similar (Sibley 1990;
Sibley et a]. 1994). The mineral phases VHMC and Ca-rich dolomite are common
mineral assemblages only in modern environments (Kocurko 1986; Wenk et a1, 1993;
Sibley et a]. 1994). These mineral phases precipitate prior to stoichiometric dolomite in
experimental studies (Nordeng and Sibley 1994; Sibley er al. 1994). Solution modelling
of natural dolomites indicates a correlation between Mg/Ca ratio of natural dolomites
and the Mg/Ca cation ratio in solution (Sass and Katz 1982; Sass and Bein 1988). In

experimental studies, a similar correlation exists (Sibley et a]. 1994). Another

75

important correlation is the increase in stoichiometry with the increase in percent
dolomite in natural dolomites (Schmidt 1965; Langbein et al. 1984). This supports the
transition from VHMC to stoichiometric dolomite (an increasing Mg content) found in
laboratory studies (Nordeng and Sibley 1994). Outcrops of partially dolomitized beds
have abrupt contacts between the limestone and the dolomitized section (Sibley et al.
1994). This observation is consistent with the model of laboratory dolomitization. In the
laboratory, dolomite is characterized by a rapid replacement period after the induction
period indicating once nucleation and grth of dolomite begins (1- 5 % dolomite
produced from calcite reagant), the reaction usually goes to completion (Sibley 1990).
Thus, abrupt contacts between limestone and dolomite in natural partially-dolomitized
limestones represents a solution front where the dolomitized side of the front had a
residence time in the solution long enough to reach the rapid replacement period.
Therefore, fluctuations in the solution front do not produce dolomite of smaller crystal
size with less time exposure to the dolomitizing solution. Past a threshold residence time,
dolomitization goes to completion on one side of the solution contact and does not on
the other side. Lumsden (1988) observed the persistence of nonstoichiometric dolomite
in sea water over millions of years. Nordeng and Sibley (1994) demonstrated the
suppression of stoichiometric dolomite nucleation by fluctuating one of the factors that
catalyze the dolomitization reaction, temperature. Their results produced VHMC and
increased the time until stoichiometric dolomite was first detected by XRD (also referred
to as the length of the induction period for that particular phase, stoichiometric
dolomite). Thus, natural observations support the experimentally-determined time

dependence of dolomitization.

76

Based on these findings, natural environments which thermodynamically favor
the precipitation of dolomite but lack any products, such as sea water, are expected to be
in a period of unstable nuclei formation of Ca-Mg carbonates, or to contain calcium
carbonate surfaces with hillocks of a Ca-Mg carbonate phase which dissolve slower than
calcite precipitated on the surface, not previously detectable by conventional methods. It
is also expected that the length of the induction period for dolomite in these

environments will vary due to the time dependence of the reaction.

APPENDIX

77

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Omovmmom.mu vamommn.o OOOOOOOH VHrmN.m OH.v mo+mm mmmu.mm Hm.On ON
OmOvOOOO.mn HVOOOOO0.0 OOOOOOOH vH|m~.m OH.v mo+mO vmmu.nH Om.OH Om
mmmmmvmm.vu nmmmvwwvu.o OOOOOOOH vHrmm.m OH.v mo+Mm Hmmm.mm Om.mm um
mmmmmvwm.vu nmmmvmwvu.o OOOOOOOH vHimm.m OH.v mo+mm mnmm.m~ HH.Hm um
HuOHNOOv.mm uOHmmOvmm.O OOOOOOOH vHimm.m OH.v mo+mv vmmw.mv ~.Hm mm
HnOHmmOv.mm OOHmmOvmm.O OOOOOOOH vHimm.m OH.v mo+mv vumm.m ~5.m mm
Ovamom0.0v mmHmomOuv.O OOOOOOOH vHImm.m OH.v mo+Mm momm.VH mm.mH v.m~
mvamomO.uv mmHmomOuv.O OOOOOOOH VHlmN.m OH.v mo+Mm Hmva.m mm.m «.mm
mHmmmmmm.vm mmmmmmmvm.o OOOOOOOH vHimN.m OH.v mo+mH Ovmm.vv mo.mv N.OH
mHmmmmmm.¢m mmmmmmmvm.o OOOOOOOH vH|m~.m OH.v mo+mH monm.mv mv «.mH
mHmmmmmm.vm mmmommmvm.o OOOOOOOH vHimN.o OH.v mo+mH OHHu.Om 50.Hm «.mH
mHmmmmmm.v~ mmmmmmmvm.O OOOOOOOH lemN.m OH.v mo+mH Oumn.vH mv.mH «.mH
mHmmmmmm.vm «mammmmvm.o OOOOOOOH vHimm.O OH.v mo+mH mnumm.n mm.O «.mH
mHmmmmmm.vm Nmmmmmmvm.o OOOOOOOH vHimm.O OH.v mo+mH movum.v mm.v «.mH
mHmmmmmm.vm «mmwmmmvm.o OOOOOOOH VHlm~.O OH.v mo+mH Hmmmv.m mm.~ N.OH
mHmOmmmm.vm «mammmmvm.o OOOOOOOH vHimN.O OH.v mo+mH O O «.mH
mwmmvuum.mm mmmvmnmmm.o OOOOOOOH vH|m~.m OH.v mo+mH mmmm.mv Om.vv OH
mwmwvnnm.mm mmmvnnmmm.o OOOOOOOH VHImN.O OH.v mo+mH mOmO.Hm OO.mm OH
vmvnmmvm.mH mvnmmvmmH.O OOOOOOOH .vHrm~.w OH.v NHHvO mvmo.mm mO.mm 5H
Hanmmvw.mH anmmvmmH.O OOOOOOOH VHimN.w mH.v NHHvO Novu.HH Hm.NH 5H
OOOOOmOOO.H OOOOOOOH0.0 OOOOOOH vHImm.m OH.v ONan O O m.mH
mposvouq x mposooua one“ Ornp3onm ommnm wroEHp m»osnoum,m»o:voum 05H“
ossHo> Houoz ossHo> Hovoz coHpmoHosz & oEDHo>.x pzmwo3

 

 

 

.5283 m 038.

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OOH H OOOOOOOH vHimm.O OH.v Oo+mO OOH OOH OOH
OOH H OOOOOOOH vHImO.O OH.v Oo+mO OOH OOH OOH
OOH H OOOOOOOH VHimN.O OH.v mo+mO OOH OOH m.vm
OOH H OOOOOOOH lem0.0 OHtv uo+mO OOH OOH m.vO
OOH H OOOOOOOH vHImN.O OH.v uo+mu OOH OOH O.NO
OOH H OOOOOOOH vHImm.O OH.v no+mn OOH OOH O.mm
OOH H OOOOOOOH vHimm.O OH.v no+mm OOH OOH O.NO
OOH H OOOOOOOH lemm.O OH.v no+mn OOOn.mO Om O.NO
OOH H OOOOOOOH vHImO.O OH.v uo+mv OOH OOH OO
OOH H OOOOOOOH vH|m~.O OH.v mo+mv OOH OOH OO
OOH H OOOOOOOH vHImN.O OH.v uo+Mm OOH OOH O.mu
OOH H OOOOOOOH vHimm.O OH.v uo+mm OOH OOH O.mu
OOH H OOOOOOOH vHim0.0 OH.v no+Mm OOH OOH 0.00
OOH H OOOOOOOH vHImm.O OH.v no+mm OOH OOH n.OO
OOH H OOOOOOOH vHImm.O OH.v uo+Mm OOH OOH O.vw
OOH H OOOOOOOH vHImO.O OH.v no+Mm mvmm.OO H0.00 O.vm
HOmvam.mm HOOHVOOO0.0 OOOOOOOH vHimN.O OH.v Oo+mv OOOO.vO vw.mm vv
HOmva0.00 HOOHvOOmm.O OOOOOOOH lemN.O OH.v mo+mv OO0.00 mm.OO vv
NOOVOOO0.00 OmvuumOm0.0 OOOOOOOH vHImN.O OH.v Oo+mm OOO0.00 OO.vO 0.00
mHUSUOHQ x mpoznogm opmu Orzpzoum mamcm vroEHp muosvou muosvoum 08H»
oEOHo> Hovoz oasHo> Hovoz coHpmoHuzz x ossHo>.x pcmHoz

 

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OOHOOnmm.vm OHOOBvam.O ~H+mH molmO.H O HOOO mmOm.mv OO.vv OH
OOHOONOO.vm mHOOmmmvm.O mH+mH molmO.H O HOOO OvOmO.HO OO.mm OH
movmmun0.0m vmmmuOON.O OH+mH OOan.H O mmmv OOvO0.0N O0.0~ 5H
muHmmun0.0m OHONOBOON.O NH+mH molmO.H O mmmv uHovu.HH HO.NH 5H
vaOnmmOH.m OnmuOHN0.0 HH+mH moImO.H O mmvv O O 0.0H
vmmOmmnOH.m OumuOHm0.0 HH+mH mosmO.H O vav O O 0.0H
NOHvOmmmm.H HOOmmmmH0.0 HH+mH moImO.H O mHHv O O OH
mmHvOmmmm.H HvOmmmmH0.0 HH+mH moImO.H O mHHv O O OH
OOOOOHOOO.H «OOHOOOH0.0 HH+mH molmO.H O «Omm O O 0.0H
OOOOOHOBO.H vaHOBOH0.0 HH+mH molmO.H O OOOO mmmuOm.m Om.m 0.0H
ONOOOOO5.H NOOOOOOH0.0 HH+mH moan.H O OOum O O 0.0H
ONOOOOO5.H NOOOOOOH0.0 HH+mH moan.H O OOum O O 0.0H
OOOmanOO.H ONHvNOOH0.0 HH+mH OolmO.H O Onmm O O OH
OOONHvuOO.H mmHvuOOH0.0 HH+mH moImO.H O Oumm O O OH
OOOOovOO0.0 mOovOOOO0.0 HH+mH moumO.H O ONOH OOHumv.m HO.m v.mH
OOOOOOOO0.0 OOOVOOOO0.0 HH+mH moumO.H O ONOH O O «.mH
OmmmanOv.O mmanOvO0.0 HH+mH moImO.H O m.onm O O O.m
mOmmumOOv.O vmanOvO0.0 HH+mH mOumO.H O m.omm O O O.m
mOOmOvmme OOOvmvmooO HH+mH moImOH O NHO O O O
mOOmOvva.O mmOvmva0.0 HH+mH OolmO.H O «HO O O O
OOOOOOOOH.O uOmNOHO0.0 HH+mH moImO.H O OHN O O O
MOONOONOH.O uOmNOHO0.0 HH+mH mOumO.H O OHO O O O
mmOmmOO0.0 OOOOOOOO0.0 HH+mH moImO.H O vO O O v
mmOmmOm0.0 mOmmOmOO0.0 HH+mH moImO.H O OO O O O
OOOOOOVO0.0 OOIMOVOOO.O HH+mH moImO.H O mmm.O O O OO.N
mOvOOOvO0.0 OOanvOOm.v HH+mH OOumO.H O OO0.0 O O OO.N
mausuoum\x mpuzuoua‘ m<np3oum ommnm O<oEHp muosvoum, mpoznona oEHp
oEOHo> HonozfloEOHo> Houoz :oHpmoHusz x oEOHo>. x uzmHo3

 

 

 

 

 

 

 

 

 

HOME SOD 5.52:8?th .382 .v 2an

 

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ONOOOmmm.mm OOOOmmmmm.O NH+mH moImO.H O Oo+mO OOH OOH m.vO
OmOOOmmm.mm OOOOmmmmm.O mH+mH moImO.H O Oo+mm Ova0.0m H0.0m O.VO
mmOOOOmN.Om mOOOOmmOm.O mH+mH moImO.H O vOHOO OumOm.vm vm.OO vv
NOOOOOON.OO OOOOOONO0.0 ~H+mH moImO.H O vOHOO OOOO0.00 O0.00 vv
vaOOON0.0m vOOOONOmm.O mH+mH molmO.H O Omqu HOOmv.mu Om.OO u.Om
vOOHOOmO.mm OOHOOmOmm.O NH+mH moImO.H O OmunO OOOO.NO OO.vO n.OO
NOOvOmmH.mm OVOmmHNm.O NH+mH moImO.H O OOOON OOH OOH OO
NOOvOmmH.mn OvOmmHmu.O NH+mH OOumO.H O OOOhN OOH OOH OO
OqumOm0.00 OvOmOmOO0.0 NH+mH moImO.H O mOmvm NONvN.HO O0.00 mm
OqumOm0.00 OVOOOOOO0.0 OH+mH moImO.H O OOmvm HmOOO.NO HO.mO mm
mOOOmOOO.vO BOONOOOv0.0 NH+mH moImO.H O ONONO vaOn.mO H0.0u Om
OOOOOOOO.vO uOOOOOOv0.0 ~H+mH molmO.H O ONOON Ovan.uH OO OH Om
vaHmOO0.00 vOHmouOO0.0 NH+mH molmO.H O OOOOH OOOON.OO OO.mO um
vaHmOO0.00 vOHmOOOO0.0 NH+mH moImO.H O OOOOH OmnOm.mm HH.Hm um
OvamOHH.NO OOvNOHHm0.0 OH+mH moImO.H O HOOOH HvOOO.mv m.HO Om
OvaOOHH.~O OOvaHHm0.0 NH+mH moImO.H O HOOOH movuOO.m mu.m Om
mOmHmmOH.Hv OOHNOOHHv.O NH+mH moumO.H O vaHH OvOmm.vH O0.0H v.m~
OOOHNOOH.Hv ONHOOOHHv.O OH+mH moImO.H O vOHHH NHOVO0.0 mm.O v.m~
summOOOm.vm OmmOOOmvm.O mH+mH moImO.H O OOOO vamO.vv O0.0v N.OH
nummOOOm.vm OOOOOOmv~.O NH+mH molmO.H O OOOO OOOOO.mv Ov N.OH
nummOOOm.vm OmmOOOmvm.O NH+mH molmO.H O OOOO OOHHu.Om 50.Hm 0.0H
bummOOOm.vN OOmOOOOv0.0 NH+mH moImO.H O OOOO HOnmu.vH Ov.OH ~.OH
unmmOOOO.vm OmmOOOOvN.O NH+mH moImO.H O OOOO uvmmmm.n mm.O m.OH
nnmmOOOm.vm OOOOOOO¢0.0 NH+mH moImO.H O OOOO mHovuO.v Om.v 0.0H
nummOOOO.vw OmmOOOmvN.O NH+mH mOamO.H O OOOO OOOOmv.m OO.~ 0.0H
nummOOOm.vN OOOOOOva.O OH+mH molmO.H O OOOO O O N.OH
mposuoum x muosvoua mum“ N‘suzoum ommzm m(oEHu mposuoua, mausuoua oEHp
oEOHo> Hobo: ossHo> Hovoz coHummHusz x oEOHo>V R uano3

 

 

 

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OOH H mH+mH moImO.H O Oo+mO OOH OOH OOH
OOH H OH+mH moImO.H O Oo+mO OOH OOH OOH
OOH H OH+mH moImO.H O Oo+mO OOH OOH m.vm
OOH H NH+mH molmO.H O Oo+mO OOH OOH m.vm
OOH H mH+mH moImO.H O Oo+mO OOH OOH m.mm
OOH H mH+mH moan.H O Oo+mO OOH OOH O.Nm
OOH H mH+mH molmO.H O Oo+mO OOH OOH m.mm
OOH H mH+mH moImO.H O Oo+mO mmmOm.OO Om O.~m
OOH .H OH+mH moImO.H O Oo+mO OOH OOH OO
OOH H NH+mH moImO.H O Oo+mO OOH OOH OO
OOOmmmmm.mm OOmmmmmmm.O mH+mH molmO.H O Oo+Mv OOH OOH O.mu
OOOmmmmm.mO mOmmmmmmm.O NH+mH moImO.H O Oo+mv OOH OOH O.Nu
vmmOmmmm.mm mmOmmmmmm.O NH+mH OOan.H O Oo+mm OOH OOH n.mO
vmmOOmmm.mm OmOmmmmmm.O OH+mH moamO.H O Oo+mO OOH OOH 0.00
mposvoua x mposuouq oumu m.cu3oum Ommcm O<oeHu muosvouq muosvoua mEHu
ossHo> Honor oESHo> Houoz coHpmoHunz & oEOHo>V x uanoz

 

 

 

 

 

 

 

 

 

 

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OOOOOOOH.OH vOOOOHOH.O OH+mH Oolmv O u.vOm OOOO.Hm OO.mO OH
OOvaOOH.m vaOOHO0.0 OH+mH OOnMv O OOO OvO0.00 O0.00 OH
mHmovaOH.m movaOHm0.0 OH+mH OOqu O OOO OO¢O.HH H0.0H OH
Hmummmmm0.0 OummmmOO0.0 OH+mH OOumv O m.OOO O O 0.0H
Hmuummmm0.0 OummmmOO0.0 OH+mH Oolmv O m.OuO O O 0.0H
HHOOvOOV0.0 OOvmvaO0.0 OH+mH Oolmv O BOO O O OH
HHOOvmva.O OOvavOO0.0 OH+mH Oole O OOO O O OH
VOOOOHOO0.0 OOOHOOOO0.0 OH+mH OOumV O O.HOO O O m.OH
vOOOOHOO0.0 mmuHOOOO0.0 OH+mH OolmO O O HOO OOOO0.0 O0.0 0.0H
OOOHOmvmu.O HHOmvmuO0.0 OH+mH OOqu O O.HvO O O 0.0H
OOOHOmvmu.O HHOmvmnO0.0 OH+mH OolmV O O.HvO O O 0.0H
OOOOOOO0.0 uOOmmmmO0.0 OH+mH Oole O OOO O O OH
OOOOmmmu.O nOOmmmuO0.0 OH+mH OolmV O OOO O O OH
OOOvOmOO0.0 OvOmOOOO0.0 OH+mH Oolmv O O.vOH OHuOv.m HO.m v.OH
OOOvOOOO0.0 OVOOOOOO0.0 OH+mH Oolmv O O.vOH O O v.OH
mmOOvuOOm.O uOvaOmO0.0 OH+mH Oole O H0.0m O O 0.0
OOmOvOOO0.0 mOvaOmO0.0 OH+mH OOan O H0.00 O O m.m
OmvuOOOH0.0 vaOOHOO0.0 OH+mH OOqu O VO O O O
OmvuOOOH0.0 vuOOOHOO0.0 OH+mH OOnmv O vO O O O
HOOOOOOHH.O OOOOOHHO0.0 OH+mH OOqu O OO O O O
HOOOOOOHH.O nnOOOHHO0.0 OH+mH OOnmv O OO O O O
OOOOOOOO0.0 OOOOOOOO0.0 OH+mH Oolmv O OH O O v
OOOOOOOO0.0 OOOOOOOO0.0 OH+mH Oolmv O OH O O v
HOOOOOvH0.0 uOOOvHOO0.0 OH+mH OOumv O OOm.v O O O0.0
HOOOOOvH0.0 OOOOVHOO0.0 OH+mH Oolm¢ O OOm.v O O O0.0
mposvouawx muosvoua Luzoum oamnm O<oEHp muosvoum,mpozvoga‘ 08H»
mEOHo> Hovoz_oE:Ho> Hovoz coHumoHonz & oEOHo>,$ ucmHoz

 

HOME SOD OEEHEOOOOEH 382 .O 035.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

vaHHvOH.uv vHHHvOan.O OH+mH Oole O OmmH mmOm.vm v0.0m vv
vaHHvOH.uv vHHvaan.O OH+mH Oolmv O OOmH OO0.00 O0.0m vv
mOOvOOO0.0m OOvOOOOOm.O OH+mH OolmO O vmvH OOmv.mn Om.OO u.Om
HOOVOOO0.00 OOVOOOOO0.0 OH+mH Oole O OOVH OOO0.00 OO.vO n.Om
HnHHHvO0.00 OHHHvOOO0.0 OH+mH OOImv O OOO OOH OOH OO
HnHHHvO0.00 uHHHvOOO0.0 OH+mH OOIMv O OOO OOH OOH OO
vOHuanO.vO OHuumOOv0.0 OH+mH Oole O HvO OOvO.HO O0.00 OO
vOHnumOO.vO OHummOOv0.0 OH+mH Oolmv O HvO mOO0.00 HO.mO OO
OHvOVOO0.00 HvaOOOO0.0 OH+mH Oolmv O u.OOu mOOn.mO Hm.On OO
mHvaOO0.00 HvaOOOO0.0 OH+mH OolmO O 0.00n vau.uH O0.0H OO
mmvaOum.HO vvaOumH0.0 OH+mH Oolmv O OOO HOO0.00 OO.uO 5O
mmvaOnm.HO vvaOumH0.0 OH+mH Oolmv O mOn OOO0.00 HH.HO 5O
OnvaHO0.0H nvaHOOOH.O OH+mH OOqu O 0.000 va0.0v O.HO OO
OuvaHO0.0H mvaHOOOH.O OH+mH Oolmv O 0.000 vuOO.m Ou.m OO
OOnOOOH0.0H OOOOOHOOH.O OH+mH Oole O v.OOO OOOO.vH O0.0H v.OO
OOOOOOH0.0H mmOOOHOOH.O OH+mH OOIMv O v.OOO HOVO0.0 mm.O v.OO
HOOOOHO0.0H OOOOHOOOH.O OH+mH OOumv O 0.0mm Ova.vv m0.0v 0.0H
HOOOOHOm.OH OOOOHOOOH.O OH+mH OOIMv O m.Omm OOOO.mv Ov 0.0H
HOOOOHO0.0H OOOOHOOOH.O OH+mH OOumV O m.Omm OHH0.00 nO.Hm 0.0H
HOOOOHO0.0H OOOOHOOOH.O OH+mH Oolmv O m.Omm OOOO.VH mv.OH 0.0H
HOOOOHO0.0H OOOOHOOOH.O OH+mH OOumv O m.Omm Oanm.u mm.O 0.0H
HmOmOHOm.OH OOOOHOOOH.O OH+mH OOumv O m.Omm OovnO.v Om.v 0.0H
HOOOOHO0.0H OOOOHOOOH.O OH+mH Oole O m.Omm HOOmv.O O0.0 0.0H
HmOmOHOm.OH OOOOHOOOH.O OH+mH OOnMv O 0.0mm O O 0.0H
OOOOOOOH.OH vaOOHOH.O OH+mH OOan O O.VOO OmOO.mv OO.vv OH
muosvoum x muosvoua cpzoum oamcm O<oEHp muosvoua mposvoua oEHp
ossHo> Hocoz oEOHo> Hovoz :oHpmoHosz x oEOHo>.x pcmHoz

 

 

 

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OvaOOmm.mm OOOOOOOO0.0 OH+mH Oolmv O OOHOO OOH OOH OOH
OvaOOOO.mm OOOOOOOO0.0 OH+mH Oolmv O OOHOO OOH OOH OOH
HovamOO.vm vamOOvm.O OH+mH OOnmv O mOOO OOH OOH m.vm
HovamOO.vm vamOOvm.O OH+mH OOumv O OOOO OOH OOH m.vm
OOOOmmHO.vm HOOmmHOvm.O OH+mH Oolmv O OVOO OOH OOH 0.0m
OOOOOOHO.vm HOOmmHOvm.O OH+mH Oole O ovOO OOH OOH 0.0m
OOOOOOHO.vm HOOOOHOv0.0 OH+mH OOumv O ovOO OOH OOH 0.0m
OOOOOOHO.vO HOOmmHOvm.O OH+mH OOnmv O OvOO mnOm.Om Om m.Om
OOHHOO0.00 OOHHOOOO0.0 OH+mH Oole O OOVO OOH OOH OO
OOHHOO0.00 OOHHOOOO0.0 OH+mH OolmV O OO¢O OOH OOH OO
OOOnHOO0.00 OOOHOOOO0.0 OH+mH Oole O OOOO OOH OOH 0.0n
OOOOHOO0.00 OOOHOOOO0.0 OH+mH OOumV O OOOO OOH OOH 0.0n
mOmvuOO.mu mOmvnOOmn.O OH+mH OOImv O OOOv OOH OOH n.mO
OOmvuOO.mu mOmvnOOmm.O OH+mH OOqu O OOOv OOH OOH u.mO
uOuOvOmm.vn nuOvOmmvn.O OH+mH OOImv O HmHv OOH OOH m.vO
nOnOvOmm.vu OOOVOmmvn.O OH+mH Oole O HOHv OvO0.0m H0.0m m.vO
muosvoua x muosvoua cusoum mamcm O<mEHp muosvoua mausvoua 08H»
oEOHo> Hovoz oEOHo> Hovoz :oHpmmHusz & oEOHo>.x ucmHoz

 

 

 

.8253 m 035

LIST OF REFERENCES

86

List of References

Avrami, Melvin, 1939, "Kinetics of Phase Change. 1 General Theory W
Wigs, vol. ‘7, p. 1103- 1112.

Avrami, Melvin, 1940, "K metros of Phase Change. [1 Transformation- Time Relations for

Random Distribution of Nuclei" WWW, vol. 8, p. 212 -
224.

Baker, P. and Kastner, M., 1981, "Constraints on the formation of sedimentary dolomite, "
Science, vol. 213, p. 214 - 216.

Bartlett, Timothy R 1984 WWW:

WWW Masters Thesis
Michigan State University.

Bullen, Susan B. and Sibley, Duncan F ., 1984, "Dolomite selectivity and mimic
replacement", (1951ng, vol. 12, p. 655 - 658.

Burton, W. K. ,Cabrera, N. ,and Frank, F. C, 1951, "The Growth of Crystals and the

Equilibrium Structure of their Surfaces", WW

mmmmmamamsmmm vol. 243, set. A. p. 299 -
358.

Busenburg, E. ,and Plummer, L. N. 1982, " T he kinetics of dissolution of dolomite in C0,-

H20 systems at l. 5 to 65" C and 0 to 1 atom PC02,"Am:nQan_J_Q]mLQ£Sfl§n§§,
vol. 278, p. 1235- 1252

Carlson, William D., 1983, "Aragonite-Calcite Nucleation Kinetics: An Application and

Extension of Avrami T ransformation 7heory",_1qumn1_qf_Qe_nggy, vol. 91, p. 57 -
71.

Christian, J.W., 1975, I. -
Press, p. 1 - 587.

 

, Pergamon

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Dove, Patricia M. and Hochella, Jr., Michael F ., 1992, "In situ investigation of near-
equilibrium calcite precipitation by atomic force microscopy", Wk
Interaction, editors Kharaka and Maest, Balkema, p. 141 - 144.

F ouke Bruce W. and Reeder, Richard J., 1992, "Surface structural controls on dolomite

composition. Evidence from sectoral zoning", WW
Aggvol. 56, p. 4015- 4024.

Fouke, B. W, 1994, "Deposition, diagenesis and dolomitization of Neogene Seroe Domi

Formation coral reef limestones on Curacao, Netherlands Antilles" ,hflzljgamm
' ‘uo , vol. 133,182 pages.

 

Gaines, A, 19780, "Dolomitization Kinetics," in Zenger, D. H, Dunham, J. B. ,and

EtifingtomeL eds 29me
W P 123-137

Goldsmith, Julian R. and Graf, Donald L., 1958, "Structural and Compositional
Variations in Some Natural Dolomites", WW, vol. 66, p. 678 -
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Gratz, A. J., Hillner, P. E., and Hansma, P. K. 1993, "Step dynamics and spiral growth on
calcite" Wm vol 57 P 491- 495

Greg, Jay M. ,and Sibley, Duncan F. 1984, "Epigenetic Dolomitization and the Origin

of Xenotoptc Texture ,W, vol. 54, no. 3, p. 908 -
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