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Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

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The staurolite enigma solved.

Mohamed Amine Marzouki¹, Bernd Souvignier¹, Massimo Nespolo²

¹Radboud University Nijmegen, Faculty of Science, Mathematics and Computing Science, Institute for Mathematics, Astrophysics and Particle Physics, Postbus 9010, 6500 GL Nijmegen, The Netherlands.

Acta Crystallographica. Section A, Foundations and Advances

|May 14, 2015

Summary

This summary is machine-generated.

Staurolite twinning, a mineralogical puzzle, is explained by a new hybrid theory. The Saint Andrews cross twin is more frequent due to superior cation site restoration, resolving its higher occurrence.

Keywords:

Greek cross twin Saint Andrews cross twin staurolite twinning

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Area of Science:

Mineralogy
Crystallography
Materials Science

Background:

Staurolite exhibits frequent twinning, with two common forms: the Saint Andrews cross twin and the Greek cross twin.
The observed frequency of these twins contradicts traditional twinning theories, particularly the reticular theory, due to differing twin indices.

Purpose of the Study:

To elucidate the crystallographic reasons behind the differing occurrence frequencies of staurolite twin laws.
To reconcile the observed twinning patterns with existing theories of crystal twinning.

Main Methods:

Analysis of the (pseudo)-eigensymmetry of crystallographic orbits in staurolite.
Application of the hybrid theory of twinning to explain complex twin structures.
Quantitative assessment of sublattice restoration for both anion and cation sites under different twin laws.

Main Results:

Both Saint Andrews cross and Greek cross twins demonstrate restoration of the anion substructure, explaining the overall frequency of staurolite twinning.
The Saint Andrews cross twin exhibits significantly higher quasi-restoration (45%) of cation sites compared to the Greek cross twin (19%).
The hybrid theory reclassifies the Saint Andrews cross twin as a hybrid twin with an effective twin index of 6.0.

Conclusions:

The higher occurrence frequency of the Saint Andrews cross twin in staurolite is attributed to its superior ability to restore cation sites.
The findings provide a comprehensive explanation for staurolite twinning, integrating crystallographic symmetry analysis with twinning theories.