Chemistry Reference
In-Depth Information
Repeating this procedure for a few other temperatures and analyzing the zero-field
spectra in a consistent way a complete picture of the hyperfine fields of greigite
and smythite could be determined.
Other examples of the application of external-field MS to improve the spectral
resolution in the characterization of soils are described by De Grave et al. [
278
].
3.7.5 Extraterrestrial Samples
Although the title of this chapter refers to applications of MS in earth sciences, one
cannot exclude to mention briefly the MS investigations of soils and rock materials
which are not strictly connected to the planet Earth.
First of all, a lot of extraterrestrial material has reached the Earth by means of
meteorites. These meteorites are in 85 % of the cases so-called chondrites, which
contain predominantly particles or chondrules that are composed of silicate min-
erals, such as olivine and pyroxene, and that are surrounded by some glassy or
crystalline feldspathic material. Sulfides such as triolite are also present. However,
the most interesting meteorites are the iron meteorites containing Fe-Ni alloys
[
279
,
280
]. In this kind of meteorite 1:1 crystallographically ordered Fe-Ni alloys
(tetrataenite) have been discovered [
281
,
282
], which has never been observed for
terrestrial variants. In that respect, the Ni-rich Santa Catharina meteorite, which
was found in Brazil in 1875, received special attention and has been thoroughly
examined by MS [
283
,
284
] and by MS in applied magnetic fields [
285
]. The
central singlet, manifestly present in the RT spectrum, has been shown to exhibit a
small hyperfine field at low temperatures (Fig.
3.51
). It has in a later stage been
assigned to a low-spin Fe-Ni phase as an intergrowth of low-spin c-Fe(Ni) and
tetrataenite and has been proposed as a new mineral, called antitaenite [
286
].
Secondly, different space programs for the exploration of the Moon were ini-
tiated in the sixties of the former century. During the American manned Apollo
Fig. 3.51 RT spectrum of a
sample of the Santa Catharina
meteorite showing the sextets
of ordered 50-50 Fe-Ni (dash)
and disordered 50-50 Fe-Ni
(dots) and the singlet of the
paramagnetic 28 %
Ni phase (adapted from [
284
])
