Chemistry Reference
In-Depth Information
Table 3.10
Representative hyperfine parameters at RT of some iron sulfates
Mineral
Formula
Fe site
d
Fe
(mm/s)
D (mm/s)
Fe
2
þ
oct
Szomolnokite
FeSO
4
.H
2
O
1.18-1.27
2.67-3.07
(Fe
2+
tetr)
0.23
0.69
(Fe
3+
oct)
0.55
0.38
Fe
2+
Rozenite
FeSO
4
.4H
2
O
oct
1.27
3.33
(Fe
2+
oct)
0.37
1.15
(Fe
2+
tetr)
0.20
0.48
Fe
2+
Melanterite
FeSO
4
.7H
2
O
oct
1.25-1.27
2.7-3.5
Fe
3+
Kornelite
Fe
2
(SO
4
)
3
.7H
2
O
oct
0.47
0.45
Fe
2+
oct
1.18-1.32
1.57-1.62
(Fe
2+
tetr)
0.21
0.67
Fe
3+
Coquimbite
Fe
2
(SO
4
)
3
.9H
2
O
oct
0.46-0.48
0.33-0.36
(Fe
3+
tetr)
0.1
0.67
FeSO
4
.Fe
2
(SO
4
)
3
.14H
2
OFe
2+
Römerite
oct
1.27-1.30
3.31
Fe
2+
oct
1.25-1.28
2.71-2.75
Fe
3+
oct
0.39-0.43
0.35-0.39
(Fe
3+
tetr)
0.1
0.66-0.84
K
2
Fe
8
Al(SO
4
)
12
.18 H
2
OFe
2+
Voltaite
oct-M2
1.20
1.56-1.62
Fe
3+
oct-M1
0.50
0.13-0.18
Fe
3+
oct-M2
0.36
1.06-1.18
Fe
3+
Jarosite
KFe
3
(SO
4
)
3
(OH)
6
oct
0.38
1.23
Table
3.10
summarizes representative hyperfine parameters for a number of
sulfate minerals. The data are taken from various authors as collected by Stevens
et al. [
158
] and from others [
159
-
162
].
Apparently, four kinds of doublets may be encountered in sulfates: one or two
Fe
2+
doublets with hyperfine parameters in the range d
Fe
= 1.1-1.3 mm/s and
D = 2.6-3.3 mm/s; one Fe
2
þ
doublet with d
Fe
& 0.2 and D = 0.65-0.70 mm/s;
one Fe
3
þ
doublet with d
Fe
= 0.3-0.5 and D = 0.4-0.5 mm/s and one Fe
3
þ
doublet
with d
Fe
= 0-0.1 and D = 0.6-0.8 mm/s.
3.4.3 Carbonates
Siderite, FeCO
3
, has a rhombohedral structure and contains divalent iron in the high
spin state. The magnetic structure is antiferromagnetic with a low Néel temperature
of 38 K. At room temperature as well as at 80 K a doublet is observed with hyperfine
parameters d
Fe
= 1.2 mm/s, D = 1.79 mm/s at RT and d
Fe
= 1.36 mm/s,
D = 2.04 mm/s at 80 K. In contrast to X-ray diffraction the Mössbauer spectra are
not distinctively influenced by substitution of Mg and Mn for Fe [
163
], although there
are indications that Ca
2
þ
provokes an asymmetry in the lineshape, pointing to a
second doublet with larger quadrupole splitting [
66
]. The siderite spectra are mostly
asymmetric, namely, one line is deeper than the other one, whereas the widths are the
