Clays and Clay Minerals. 1970,Vol.18,pp. 187-195. PergamonPress. PrintedinGreatBritain
M I C A W E A T H E R I N G R A T E S AS R E L A T E D
MICA TYPE AND COMPOSITION*
TO
R. A. LEONARDt and S. B. WEEDS
Department of Soil Science, North Carolina Agricultural Experiment Station, North Carolina State
University, Raleigh, N.C. 27607
(Received 17 N o v e m b e r 1969)
Abstract- Potassium release rates from micas varying widely in type and composition were measured.
A sodium tetraphenylboron solution was used as the extracting agent. Muscovites were found to be
two orders of magnitude more stable than a naturally occurring phlogopite and biotite. Synthetic
fluorphlogopite was as stable as some muscovites. Lepidolite was the most stable mica. Primary
factors affecting mica stability are thought to be: Hydroxyl bond orientation, isomorphous replacement
of OH- by F-, the stronger Lewis base, and structural factors that lead to compression or stretching of
the K---O bond.
INTRODUCTION
WEATHERING of mica by K + depletion has been the
subject of many investigations. Most investigators
have viewed mechanisms involved in vermiculite
formation from mica weathering as primarily those
of ion exchange with concurrent or subsequent
structural charge reductions (Barshad, 1948; Raman
and Jackson, 1965). The K + exchange mechanism
apparently is a diffusion-controlled process dependent on the salt concentration used in the replacement (Mortland, 1958; Sumner and Bolt, 1962;
Reed and Scott, 1962).
Barshad (1948), Mortland (1958) and Bassett
(1960) have found that K § can be replaced in
biotites and phlogopites by leaching with aqueous
salt solutions. This procedure cannot be used to
replace K § from muscovite, however, Bassett
(1960) explained this difference in stability as being
due to differences in orientation of structural
hydroxyls. He postulated that .the oxygen-proton
bond directed towards the K + ion in the case of
trioctahedral micas leads to a repulsive force which
decreases the bonding energy of K +.
The data of Reed and Scott (1962) showed that
for the same particle size fraction, the K + release
rate from muscovite in a sodium tetraphenylboron
*Published with the approval of the Director as Paper
No. 2929 of the Journal Series.
tResearch Soil Scientist, USDA, Watkinsville,
Georgia 30677 (formerly Instructor, Department of Soil
Science, North Carolina State University, Raleigh, North
Carolina.
:~Professor of Soils, North Carolina State University,
Raleigh, North Carolina.
(N aTPB) solution was approximately two orders of
magnitude slower than from a biotite.
Cook and Rich (1963), using boiling salt solutions
and molten lithium nitrate, demonstrated that there
may be a wide range in stabilities within the dioctahedral group. They suggested that this may be
related to the differences in ionic substitutions
which usually occur in the mica lattice.
Recently, Rausell-Colom et al. (1965) determined K § "solubilities" for a wide range of mica
types. Their values ranged from 1-5 x 10-~ M to
2 x 10-4M, consistent with earlier findings of
Mortland (1958). They were unable, however, to
replace any K + from a muscovite, lepidolite or
synthetic fluorphlogopite. It was reasoned that
traces of K + from glass reaction vessels prevented
any replacement. Their "solubility" values were
inversely related to F - contents of the trioctahedral
micas. This observation is consistent with the
conclusion of Bassett (1960) since when F replaces O H - , the repulsive force between the K §
ion and a proton is not present. Rausell-Colom et al.
(1965) observed no other adequate relationships
between stability and compositional variables such
as ferrous iron content or tetrahedral vs. octahedral charge. Thus, they concluded that orientation of the O H - group plays the dominant role in
determining mica stability.
In view of recent mica structure determinations
which show wide departures from the ideal classical structure, it is entirely possible that many of the
observed differential weathering rates may be
explained by structure variables. Radoslovich
(1963) considered that the relative stability of the
2M1 muscovite must be related to the unique way
187
188
R . A . LEONARD and S. B. WEED
in which K + is locked into interlayer positions.
Brown (1965) postulated that much of the stability
variation can be accounted for by a variation in the
K---O bond length.
Since charge reduction apparently takes place
during weathering (Raman and Jackson, 1965), the
rate of charge reduction may also affect the
weathering rate if the reduction takes place
simultaneously with K removal.
Most observations of rates of K release were
made under conditions where many of the variables
were either not specified or not measured. This
research was initiated to provide additional information on K release rates under controlled conditions. The experiments were conducted so as to
provide direct numerical comparisons over a wide
range of mica types.
MATERIALS AND METHODS
All studies were conducted on specimen grade
micas. These consisted of eight muscovites collected near mining excavations in western N o r t h
Carolina; one biotite, one phlogopite, and one
lepidolite obtained from Ward's Natural Science
Establishment, Rochester, N e w York; and a
synthetic fluorphlogopite obtained from the
Mycalex Corporation, Caldwell, N e w Jersey.
Sample description and identification are given in
Table 1. Each mica was chemically analyzed for
major constituent elements (Shapiro and Brannock,
1956). Structural formulae for each mica computed
from the analyses are given in Table 2.
The micas were wet-ground in a ball mill, and
1-5 ~ size classes were fractionated by sedimentation. All rate studies were conducted on this
size class. Particle size distributions within the
1-5/z class (Table 3) were determined by the
hydrometer method (Day, 1956).
The micas were characterized structurally
using X-ray diffraction (Table 4). Preferred particle
orientation in specimens for X-ray analysis was
overcome by mixing the samples with a thermoplastic organic cement, essentially as described by
Brindley and Kurtossy (1961). The degree of triad
rotation in the tetrahedral layer was calculated
according to the method of Radoslovich and
Norrish (1962).
Potassium release rates were studied using a
solution 0-2 M in sodium tetraphenylboron
(NaTPB), 1 M in NaC1, and 0.01 M in disodium
ethylene diaminetetraacetate ( E D T A ) as the
extracting agent (Reed and Scott, 1962). The pH of
the solution was adjusted to 7.5. A ratio of 50 ml of
extracting solution to 2 g of mica was used in all
extractions. The samples were maintained at 27.5 ___
0-2 ~ and continuously mixed during K § extraction.
A t the end of the appropriate reaction time a small
subsample was removed and added to a relatively
large volume of 1 N NH4CI solution to quench the
reaction. The precipitated K + was then removed
from the mica suspensions by repeated washings
using centrifugation with a 1 N NH4CI-50% acetone solution (Reed and Scott, 1961). Potassium
remaining was measured by an X-ray emission
technique (Weed et al., 1969).
After completion of the rate studies the remaining
suspensions of mica-NaTBP were allowed to mix
for a total of 30 days so that layer charge changes
with exhaustive K § depletion could be determined.
A t this time the remaining material was treated for
K + removal from the suspensions and saturation
with Sr 2+ as described previously (Leonard and
Weed, 1967). Using this material, cation exchange
Table 1. Mica description, identification, and sampling location
Sample
identification
Description
Ml
White muscovite
M2
M3
M4
M5
Light ruby muscovite
White muscovite
Pale green muscovite
Pale brown-green
muscovite
Pale green muscovite
Ruby muscovite
Ruby muscovite
Dark green biotite
Lavender lepidolite
Brown phlogopite
Colorless
fluorphlogopite
M6
M7
M8
B2
LI
P1
P2
Sample source
N ear N.C. road 80 at South Toe River,
Yancey Co., N.C.
Near old Westall mine, Yancey Co,, N.C.
Hoot Owl Hollow, Mitchell Co., N.C.
Hoot Owl Mine, Mitchell Co., N.C.
Near Penland, Mitchell Co., N.C.
Deer Park Mine, Mitchell Co., N. C.
Big Ridge Mine, Haywood Co., N.C.
Iolta Bridge Mine, Macon Co., N.C.
North Burgess, Ontario, Canada (Ward's)
Colorado (Ward's)
North Burgess, Ontario Canada (Ward's)
Mycalex Corporation, Caldwell, N.J.
MICA W E A T H E R I N G RATES
189
~o66~6666~6~m6
v
o ~
~
_o
~
~666~6666~66~
v
&666~&~66~666~6
V
9
.
9
.
.
.
.
.
.
.
.
.
.
V
.
V
.
.
V ~
VV
~o
~ 6 6 6 ~ A 6 6 6 6 6 6 ~ 6
v
"6
vv
~66~A6~66o66A6
V
II
V
+
V ~
0
V
V
II
?
0
N
~
o
<
190
R . A . LEONARD and S. B. WEED
Table 3. Particle size distribution of micas within the
1 - 5 / z class limits
Per centbyweightofparticles
in size classes(~)
Mica
< 2
2-3
3-4
4-5
> 5
Mean particle
size(/x)
MI
M2
M3
M4
M5
M6
M7
M8
B1
B2
L1
P1
P2
13
19
19
10
14
15
19
12
17
6
19
13
18
23
25
22
25
26
25
19
15
25
12
27
16
32
32
25
35
31
34
26
36
36
37
23
28
24
23
26
25
20
30
17
26
36
37
14
34
17
32
19
6
6
4
4
9
8
0
0
7
25
9
15
8
3-15
3"33
3"09
3"38
3.24
3-30
3"10
3.42
3"11
4.07
3"11
3.64
3'08
were then assigned to expanded layers, the fraction
of which was computed from the residual K §
content. The N a § which remained in expanded
layers was apparently due to incomplete Sr 2+
saturation. The remaining N a + was generally less
than 5 per cent of the CEC.
RESULTS
Table 4. Crystal structure characteristics of micas
Mica c sin/3*
M1
M2
M3
M4
M5
M6
M7
M8
B1
B2
P1
P2
L1
(•)
20.09
20.02
19-99
19"91
19"97
19'97
20.04
19"99
10"10
10"10
10"08
10.01
19.81
bob s
aeale.
(A) (Degrees)
8 . 9 9 4 14.85
9 . 0 0 3 14.78
8 . 9 8 7 14.90
9 " 0 2 6 13"73
9 " 0 1 3 14"47
9 " 0 3 5 13"58
9 " 0 1 3 14"22
9"008 14"18
9 " 2 4 6 11"00
9 " 2 4 0 11"67
9 " 2 0 0 12"28
9.184
9.27
9.028
9.13
Polymorpht
2M1
2M~
2M~
2M1
2M1
2M1
2M1
2M1
It was found convenient to express the K §
release data in t er m s of t h e equation:
~00( 1 - - l n ~ 0 0 ) = 1--ktrb
derived by Reed and Scott (1 962)
where Q is the amount of K + remaining at time, t,
Q0 is the initial K + content,
rb is the mica particle radius, assuming
cylindrical particles,
and k is the rate constant.
Th e equation was derived assuming a cylindrical
model for the particle and assuming that K + diffusion from interlayer positions is the rate limiting
step. Th e equation also assumes a uniform weathering from moving in from the particle edges with
time. Some of the data are shown in Figs. 1 and 2,
the quantity
being plotted vs. t. Th e slope of the supposedly
linear relationship obtained is equal to --k/rb. The
value of k, which is a numerical estimate of the
1M or 3T
IMor3T
2M2
*d(001) = c s i n / 3 .
tSmith and Yoder (1956)
1 M = one-layer monoclinic
2M1 and 2M2 = two stacking sequences for two-layer
monoclinic
3T = three-layer trigonal.
capacities (CEC) were determined by the X-ray
emission procedure of Weed and Leonard (1963).
Residual N a + and K § were determined by flame
photometric procedures after sample dissolution
with H F (Shapiro and Brannock, 1956). Charge on
expanded layers was computed by first assigning
all the residual K § and part of the residual N a + to
nonexpanded layers (Mehra and Jackson, 1959).
Sodium in nonexpanded layers was assumed to be
present at the same ratio to K + as the original
mica~ The remaining N a § and exchangeable Sr 2§
1.0
"8
old
.6
c"
I
.4
-2
......
0
I
!
I
I
100
200
300
400
Time ( h r )
Fig. 1. Diffusion plots for K § release from various micas.
MICA WEATHERING RATES
1.OI
"8
.e
t-"
I
oTd . 4
. 2 84
I
O
I
I
0.50
I
I
1.00
Time
I
1.50
(hr)
Fig. 2. Diffusion plots for K + release from micas P1 and
B2.
relative stability of the mica, can be obtained by
assuming rb to be equal to the mean particle size
(Table 3).
Representative data for four micas are shown in
Fig. 1. Muscovite M8 was the most resistant of the
muscovite group, and M4 was the least resistant.
The fluorphlogopite, P2, was about as resistant as
the muscovites. Lepidolite, L 1, was the most stable
mica. Micas P 1 and B2 were the least stable (Fig. 2).
The k values computed from the plots are given
in Table 5. N o t all plots were linear, as is illustrated
by the data for M4 (Fig. 1). Departure from linearity was greatest for those micas from which more
Table 5. Experimental k values calculated from a diffusion model for potassium release from micas into NaTPB
solutions at 27.5~
Mica
M1
M2
M3
M4
M5
M6
M7
M8
B2
P1
P2
Lt
-k/rb*,hr-l,•
4
14-0
12.0
6-4
29-0
13'0
16"0
5-8
5-9
2900.0
1500-0
13"0
2"3
*Slope of plot: ~o(1 - In ~0) vs. t.
--k, lz 1hr-1, • 104
4-1
3.7
2-1
8-1
4-0
5-0
1-9
1"7
700-0
400-0
4.1
0.74
191
than half of the K + was removed. That is, the plots
were most linear in the initial phases of K + removal.
Therefore, for the non-linear plots, except for P1
and P2, k was estimated from a line drawn from the
intercept to the first data point. A lag-time is indicated by the shape of the plots for P1 a n d P2. The
k for these micas was found by taking the slope of
the linear portion some time after initiation of the
reaction.
Errors in K + determination were estimated to be
approximately +__2 per cent. Errors in determining
time and temperature were usually less than + 2 per
cent over the measured interval. Considering
analytical precision alone and assuming that k
values were determined from single pairs of points
after approximately 50 per cent K § removal, as
was the case for M1, M2, M4, M5 and M6, errors
in k values are estimated to be about + 10 per cent
(Benson, 1960).
DISCUSSION
In spite of uncertainties encountered in obtaining
k values for K + release from micas, large differences were shown to exist between relative weathering rates of the different micas. Within the dioctahedral group, M8 was approximately four times
more stable than M4. The weathering rates of
trioctahedral micas varied even more. Lepidolite
L 1 was approximately 1000 times more stable than
biotite B2. Apparently there is no simple relationship between K + release rates and mica properties.
Charge reduction a n d Fe 2+ content
Gruner (1934) first postulated that positive
charges lost during removal of potassium were
compensated by oxidation of octahedral Fe 2+ to
Fe 3+ or by the substitution of hydroxyls for oxygen.
Foster (1963), after a critical examination of published analyses of vermiculites and hydrobiotites,
concluded that most of the charge reduction could
be accounted for by oxidation of Fe 2+. Therefore,
the presence of Fe 2+ may provide a mechanism of
charge reduction and enhance K § release if charge
reduction occurs simultaneously.
Mica M4, which lost K § at the fastest rate among
the muscovites, had the highest Fe 2+ content of the
dioctahedral micas. However, M8, which lost K § at
the slowest rate, did not have the least amount of
Fe 2+. No apparent relationship between Fe 2+ and
K + release existed within the muscovite group.
Biotite B2 released K § at a faster rate than did
phlogopite PI. N o general conclusions should be
made based only on results from these two micas.
However, as will be discussed later, the biotite may
have released K + more rapidly because of its
longer K---O bond rather than because of its high
content of oxidizable Fe 2+. RauseU-Colom et al.
192
R.A. LEONARD and S. B. WEED
(1965) found no relation between Fe 2+ and rates of
K § release even for a group of high iron biotites.
Apparent charge reduction occurred with K §
replacement for all micas used in this study (Table
6). For the most part, this reduction in charge
could not be accounted for by oxidation of Fe z+ in
the octahedral layer of the mica. Since charge
reduction was apparently not related to Fe 2+ content, it is reasonable that no relationship should
exist between Fe ~+ contents and K + removal rates.
A relation between mica stability and magnitude of
tent with proposal of Bassett (1960) and observations of RauselI-Colom et al. (1965). However, this
observation alone does not necessarily indicate
that the proton orientation in P1 weakens the
attractive force for K § When F-, the stronger
Lewis base, is present in micas, the attractive force
for K + which is positioned over the hexagonal or
ditrigonal opening in the oxygen layer may be
greater than the attractive force between O H - and
K + regardless of the particular O - - H polarization.
This factor is not widely recognized.
Table 6. Charge characteristics of weathered micas
Mica
Initial mica
charge
(me/100 g)
Residual K §
content
(me/100 g)
Charge on
expanded
layers
(me/100 g)
Per cent
charge
reduction
M1
M2
M3
M4
M5
M6
M7
M8
B2
P1
P2
L1
262
232
232
233
243
233
245
237
198
208
237
254
25
25
37
21
22
21
37
39
4
8
19
96
165
161
182
174
156
179
183
184
158
169
220
128
37
31
22
25
36
23
25
22
21
19
7
50
charge reduction still may be expected regardless
of the exact mechanism of reduction, but this
relationship was not apparent in this study. With
the exception of lepidolite L 1, there is a tendency
for observed charge reduction to be greatest for
least stable micas; however, this may be a result of
mica instability rather than a cause. To explain
observed charge reduction, some mechanism other
than Fe 2+ oxidation must be postulated. A possible
explanation is to assume proton incorporation into
the crystal lattice of mica as proposed by Raman
and Jackson (1965). Magnitudes of charge reduction observed in this study are consistent with their
observations. They proposed that the incorporated
proton was associated with oxygens of tetrahedra
occupied by AI 3+. Conceivably as charge reduction
proceeds, the AP + ion itself may be replaced by a
hydroxyl tetrahedron.
Hydroxyl orientation and F- content
The major compositional difference between
micas P 1 and P2 was in their O H - and F - contents.
Mica P2 had complete replacement of structural
O H - by F-. Apparently the presence of F - increased the stability of P2 to K + removal, consis-
Biotites were found by Bassett (I 960) and others
to have some of their O H - groups directed as in
muscovite, presumably due to the presence of
some vacant octahedral sites. On the basis, biotites
might be expected to be more stable than phlogopites if O - - H polarization weakens the attractive
force for K +. However, P1 was more stable than
B2. Therefore, some other factor must be responsible for the difference in K + release rate between
P1 and B2.
A surprising result of this study was the marked
stability of lepidolite L 1 compared to the stability
of other trioctahedral micas. However, recent work
of Farmer and Russell (1964), who used infrared
absorption spectroscopy, indicated that the lepidolite in their study may actually belong in the
dioctahedral family if classified according to the
appearance of its infrared absorption pattern. They
noted that, presumably due to the marked difference in valency of octahedral AP + and Li +, the
octahedral layer of lepidolite had low symmetry
similar to that found in dioctahedral mica. The high
symmetry of the trioctahedral micas leaves certain
S i - - O bending modes inactive in the infrared and
other S i - - O modes are nearly degenerate and
MICA WEATHERING RATES
couple with the octahedral cations to give two
strong closely spaced absorption bands. This
characteristic in the absorption pattern was not
found for lepidolite. Farmer and Russell (1964)
stated no conclusions concerning orientation of
O H - groups in lepidolite since in their sample
most of the O H - had been replaced by F - . Due to
the lower symmetry of the octahedral layer and to
the lower polarizing power of Li § in comparison to
A P + or Mg 2+, structural hydroxyls of lepidolite
may be oriented as in muscovite, or are at least
somewhat tilted away from the normal to the tetrahedral sheet. On this basis, then, lepidolite should
be about as stable to K § release as muscovite. The
observation was, however, that lepidolite was even
more stable than muscovite. In the lepidolite
studied, about 15 per cent of the O H - groups were
substituted by F-. The presence of F - would be
expected to add additional stability through increasing the bonding energy of the K § ion which
lies directly above the F - . A b o u t 10 per cent of the
interlayer positions were also occupied by Rb +. It
is not known if the presence of Rb + should increase
stability of the K + - R b + interlayer. If adding F - to a
dioctahedral-like structure increases K + bonding
energy, a fluormuscovite would be expected to be
extremely resistant, and in comparison become
even more resistant than a fluorphlogopite. This
implies that some factor or force in addition to O H orientation or replacement by F - must be increasing stability of natural dioctahedral micas relative
to natural trioctahedral micas.
Tetrahedra rotation
Radoslovich (1963) postulated that the relative
stability of 2M~ muscovite was related to the
unique way in which K § is "locked" into interlayer
positions. It was initially thought that the magnitude
of t~ would be a measure of "locking" tendencies or
compressional forces on the K---O bond. However,
no apparent relationship between a and K + release
was observed. In general, trioctahedral micas do
not exhibit tetrahedra rotation to the extent found
in dioctabedral micas and, as can be seen from this
study, the dioctahedral micas are generally more
stable than trioctahedral micas. However, the
relative mica stabilities were not related to the
magnitude of a, especially since lepidolite was
found to be most stable and had the lowest t~ due to
low tetrahedral A1. The failure ofct to predict mica
stability does however, not imply that structural
characteristics are unimportant.
K---O Bond lengths
In micas, the configuration of the interlayer
region and the K---O bond length depends on the
manner in which inter-atomic forces are balanced
193
within the crystal. Brown (1965) pointed out the
variability of the K---O bond length and postulated
that the variation observed would affect mica
stability. The structure model of oDonnay et al.
(1964) suggested a range from 2-72 A to 3.25 A for
the K - - O bond length. The variation of K - - O bond
lengths with structure and composition has recently
been better defined by Tepikin et al. (1969) and
Drits (1969). These studies generally show that the
K---O bond length in biotites is greater than that in
phlogopites, a possible reason why PI was found to
be more stable than B2.
Drits (1969) also pointed out the relationship
between O H group polarization and K - - O bond
lengths. In dioctahedral micas, K § is in an octahedral enivronment with respect to O and the K---O
distance is about 2.85 ,~. But, in trioctahedral micas
the interaction between K + and O H groups prevents the K + ion from bringing the layers sufficiently close to achieve the octahedral environment.
The resultant K - - O bond length is around 3 ,~,
significantly greater than 2.85 A. This difference in
interlayer configuration and K - - O bond lengths
must be reflected in the marked stability of dioctahedral micas compared to trioctahedral micas.
Radoslovich (1962) compared the b-dimension of
vermiculite to that of phlogopite and concluded
that the role of K + in the mica was to decrease b.
Leonard and Weed (1970) verified this conclusion
by observing that the b-dimension of phlogopite
increased with K + removal. Earlier, Burns and
White (1963) and Leonard and W e e d (1967) found
that the b-dimension of muscovite tends to contract
with K + removal. These observations are additional evidence that the K - - O bond in dioctahedral
micas is compressed relative to that in trioctahedral
micas. A s K § is released from dioctahedral micas a
slight decrease in b at the weathering front may
tend to lock the K + remaining more tightly and
retard its release. Also the increase in b at the
weathering front in trioctahedral micas may weaken
or stretch the K - - O bond sufficiently to enhance
K + release.
REFERENCES
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as revealed by base exchange reactions, X-ray analysis,
differential thermal curves and water content: Am.
Mineralogist 33, 665-678.
Bassett, W. A. (1960) Role of hydroxyl orientation in
mica alteration: Bul. Geol. Soc. Am. 71, 449-456.
Benson, S. W. (1960) The Foundation o f Chemical
Kinetics. McGraw-Hill, New York.
Brindley, G. W. and Kurtossy, Sari S. (1961) Quantitative
determination of kaolinite by X-ray diffraction: Am.
Mineralogist 46, 1205-1215.
194
R. A. L E O N A R D and S. B. W E E D
Brown, G. (1965) Significance of recent structure determinations of layer silicates for clay studies: Clays and
Clay Minerals 6, 73-82.
Burns, A. F. and White, J. L. (1963) Removal of potassium alters b-dimension of muscovites: Science 139,
39-40.
Cook, M. G. and Rich, C. I. (1963) Negative charge of
dioctahedral micas as related to weathering: Clays and
Clay Minerals 11, 47-64.
Day, P. R. (1956) Report of the committee on physical
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Trioctahedral one-layer micas, lI. Predictions of the
structure from composition and cell dimensions: Acta
Cryst. 17, 1374-1381.
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R~sum~-Les taux d'extraction du potassium de micas de types et de composition trts difftrents ont
6t6 mesurts. Une solution de tttraphtnyl-bore de sodium a 6t6 utilisge comme agent extracteur. On
a trouv6 que les muscovites 6talent de deux ordres de grandeur plus stables que la phlogopite et la
biotite naturelles. La fluorophlogopite synthttique 6tait aussi stable que quelques muscovites. La
16pidolite est le mica le plus stable. On pense que les facteurs primaires affectant la stabilit6 du mica
sont: l'orientation de la liaison hydroxyle, le remplacement isomorphe de O H - par F_, une base
Lewis plus forte et les facteurs structurels qui occasionnent la compression ou l'allongement de la
liaison K-O.
K u r z r e f e r a t - D i e Geschwindigkeiten der Abgabe von Kalium aus Glimmern, die sich in Bezug auf
Typ und Zusammensetzung stark yon einander unterschieden, wurden gemessen. Als Extraktionsmittel wurde eine NatriumtetraphenylborliSsung verwendet. Es wurde festgestellt, dass Muskowite
um zwei Gr6ssenordnungen bes~ndiger sind als ein natiirlich vorkommender Phlogopit und Biotit.
Synthetischer Fluorphlogopit war ebenso best~indig wie gewisse Muskowite. Lepidolit stellte den
best~ndigsten Glimmer dar. Man glaubt, dass die Best~ndigkeit der Glimmer in erster Linie dutch
folgende Faktoren beeinflusst wird: Orientierung der Hydroxylbindung, isomorpher Ersatz yon O H dutch F 2, die s~rkere Lewis Base, sowie strukturelle Faktoren, die Anlass zu einer Stauchung oder
Dehnung der K - O Bindung geben.
MICA WEATHERING
RATES
Pe3IOMe----H3MepeHI, I CKOpOCTHyRaYleHHH I{aJIHg H3 CJIIO~, cyIIIeCTBeHHO pa3~HqaiomHxc~ n o T~Irly
H COCTaBy. B Ka~IeCTBe3ir
areHTa IIpHMeH~IYlCgpaCTBOp HaTpHCBOrO TeTpa~HnJI6opa.
YCTaHOBYICHO, ~TO MyCKOBHTbIHa ~Ba nop~n~a yCTOI~tIHBCHI]pHpo~tHbIX ~pnoroIIHTOB H ~HOTHTOB.
CHHTeTHtICCKHI~ ~TOp~JIOrOIIHT TaIOI~C yCTO~qI4B KaK H HCKOTOpbIr MyCKOBHTbI. fleHH~IOJIHT
OKa3aJIGg HaH60~eC yCTOK'qHBO~CJHO~Oi~. BbI~CJICHbI cYle~yxoxJjHe nepBHtIHbIe ~paKTOpbI, BYIH~q~omHe
Ha yCTO~qHBOCTb CJIIO,~: opHeHTaUH8 Bo~opo~HbIX GBH3eH, H3OMOp{bHbIe 3aMeWCHHH O H - Ha F - ,
6OJICC CK~HOe 0CHOBaHHe .lhoHca, H cTpyKTypHblC ~paKTOpbI, IIpHBO~III~HC K C)KaTHIO HJIH
p a c T a x e H m o CBa3H K-O.
195