 |
| Titel |
The application of μ-XRD2 to identify gypsum whiskers in Messinian evaporites |
| VerfasserIn |
Simone Ziegenbalg, Christoph Berthold, Andreas Kappler, Jörn Peckmann  |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051213
|
|
|
|
|
|
| Zusammenfassung |
| Micron-sized crystals are difficult to identify with conventional techniques like optical
microscopy and standard XRD. Modern X-ray diffractometers combined with focussing
X-ray optics and a large 2-dimensional detector (μ-XRD2) enables the analysis of
minute mineral phases directly on uncovered thin sections. We used a BRUKER
D8-GADDS-microdiffractometer equipped with a focussing 50 μm polycapillary optic to
identify the gypsum mineralogy of delicate hair-like crystals present locally in
Messinian evaporites, which otherwise mostly consist of anhydrite. These peculiar
crystals are characterized by a length-to-width ratio considerably higher than 100 and
can therefore be regarded as whisker crystals. Gypsum whiskers typically form by
efflorescence on moist porous surfaces. The whiskers studied here project from
alabastrine gypsum into former cavities. The gypsum resulted from the hydration of
anhydrite. The whiskers are embedded in biogenic native sulphur, which filled the
cavities in the course of microbial alteration of the host lithology. The entombment by
native sulphur protected these delicate minerals against destruction by dissolution
during exposure of the evaporites on a dumping site of a former mine, where the
rocks have been sampled. To best of our knowledge, gypsum whiskers had not been
previously recognized in evaporites. Even more significant, this study emphasizes the
great potential of μ-XRD2 for sedimentary petrology, because it enables in situ
identification of micron-sized mineral phases, which cannot be identified with conventional
techniques. |
|
|
|
|
|
|