Chemistry Reference
In-Depth Information
Fig. 3.25 RT spectra of some tourmalines from the English Lake District which needed to be
fitted with 2 to 4 doublets (adapted from Eeckhout et al. [
207
])
Table 3.15
Representative hyperfine parameters at RT for cyclosilicates
Mineral
Formula
Fe site
d
Fe
(mm/s) D (mm/s)
Fe
2+
Beryl
Be
3
Al
2
Si
6
O
18
oct
1.16
2.70
(Fe
3+
oct)
0.59
0.86
Al
3
(Fe
2+
)
2
(AlSi
5
)O
18
Fe
2+
Cordierite
1.15
2.3
Ca(Fe
2+
)
3
]Al6(Si
6
O
18
)(BO
3
)
3
OH)
3
(OH)
Fe
2+
Tourmaline
(schorl)
Y1
1.08-1.10
2.50
Fe
2+
Y2
1.07-1.10
2.20-2.35
Fe
2+
Y3
+ other D
1.07-1.10
1.40-1.70
[Na(Li
0.5
Al
0.5
)
3
-Ca(Fe
2+
)
3
]Al
6
(Si
6
O
18
)(BO
3
)
3
(OH)
3
(OH)- and the dravite-schorl
series [Na(Mg)
3
- Ca(Fe
2+
)
3
]Al
6
(Si
6
O
18
)(BO
3
)
3
(OH)
3
(OH).
The spectrum of tourmaline consists basically of a quadrupole doublet with
d
Fe
= 1.1 mm/s and D = 2.46-2.48 mm/s originating from Fe
2+
on the B (Y)
sites. Although this doublet is dominant in most of the spectra in tourmalines, other
doublets are clearly observed which have been attributed to Fe
2+
,Fe
3+
and
intermediate Fe
n+
(from electron exchange processes). Additional iron in C (Z)
sites and a cis-trans isomerism in B (Y) sites may render the spectra rather
complicated leading up to five or even seven components to be used in the fits
[
202
-
207
].
RT
spectra
of
some
tourmalines
are
displayed
in
Fig.
3.25
(Table
3.15
).
3.5.5 Inosilicates
The inosilicate minerals are built up by chains of SiO
4
tetrahedra. They can further
be divided into two subclasses: the pyroxenes with single-stranded chains, having
an overall composition SiO
3
2-
and the amphiboles with double-stranded chains of
Si
4
O
11
6-
stoichiometry.
