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| Titel |
Cyclic growth and branching phenomena of calcite grown in Mg2+ containing solutions and in natural systems |
| VerfasserIn |
Felix Wiethoff, Detlef K. Richter, Rolf D. Neuser, Adrian Immenhauser, Hermann Gies, Jürgen Schreuer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136074
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| Publikation (Nr.) |
 EGU/EGU2016-17032.pdf |
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| Zusammenfassung |
| Undulosity in calcites (radiaxial fibrous calcite (RFC) and fascicular-optic fibrous calcite
(FOFC)) is a common phenomenon in paleozoic and mesozoic limestones. Despite their
importance as archives for climate reconstruction the underlying mechanisms and processes
of their formation are still poorly understood [1]. To improve the application of such archives
for climate reconstruction a better knowledge of their formation and possible alteration
scenarios is necessary.
In Mg2+ containing gel based growth experiments calcite crystals develop pathological
morphologies. The morphology can be described as a product of a geometrical selective
branching process at the rhombohedral crystal faces. Multiple sheet like building blocks
evolve at the branching crystal face; each slightly tilted in respect to their substrate. The
product is a crystal aggregate consisting out of several misoriented sub domains. In polarized
light thin section microscopy the extinction behaviour of these sub units resemble the optical
undulosity of radiaxial fibrous cements.
In a multi method approach the local Mg2+ concentration was measured using EMPA and
compared with maps of the local crystal orientation (via electron backscatter diffraction
(EBSD)) and thin section microscopy. We found that Mg2+ is enriched at the sub-domain
boundaries and deduced that lattice misfit as a consequence of impurity incorporation causes
the crystal branching.
We propose that this process is cyclic and each new misoriented sheet represents a
growth period after a phase of inhibited growth caused by crystal faces covered by
Mg2+−ions.
In comparison to natural systems we found that radiaxial-fibrous cave cements show a
pathological morphology based on the same formation principles.
[1] Richter et al. (2011) Sediment. Geol. 239, 23-36 [2] Reeder & Paquette
(1989) Sediment. Geol. 65, 239-247 [3] Davis et al. (2004) Am. Min. 89, 714-720 |
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