@misc{10481/103451,
year = {2025},
month = {3},
url = {https://hdl.handle.net/10481/103451},
abstract = {In the argillic alteration zone of the SinAbad area of the Urumieh–Dokhtar magmatic
belt (Iran), Mg-rich, Fe-poor chlorites, which crystallised at temperatures between
160 ◦C and 260 ◦C, were affected by extensive alteration to smectite mixed-layering at
the micro- and nano-scales during the retrograde evolution of the hydrothermal system.
Chlorites retain their usual optical aspect and properties, except for the index of refraction
perpendicular to the (001) layers, which becomes lower than those parallel to the layers,
producing an increase in birefringence and change in the optic and elongation signs, in comparison
to the ordinary ones for Mg chlorites. Scanning electron microscopy (SEM) maps
and compositions, and electron microprobe (EMP) analyses indicate minor but ubiquitous
Ca (and K) content. X-ray diffraction (XRD) of chloritic concentrates allowed the identification
of chlorite and tosudite. High-resolution transmission electron microscopy (HRTEM)
images show major 14 Å (chlorite), with the frequent presence of 24 Å (contracted tosudite)
individual layers and small packets up to five layers thick. Lateral change from 14 Å to
24 Å individual layers has been visualised. High-resolution chemical maps obtained in
high-angle annular dark-field (HAADF) mode confirm the existence of areas preferentially
dominated by chlorite or tosudite. The overall chemical compositions obtained by SEM,
EMP, and transmission electron microscopy (TEM) align from the chlorite to the tosudite
end-members, whose pure compositions could be determined from extreme analytical
electron microscopy (AEM) analyses. The described intergrowths and interlayers, under the
optical resolution, could provide a clue to explain changes in the normal optic properties of
chlorite, which are mentioned, but not explained, in the literature.},
publisher = {MDPI},
keywords = {Optical properties},
keywords = {Tosudite},
keywords = {Chlorite},
title = {Hydrothermal Retrogradation from Chlorite to Tosudite: Effect on the Optical Properties},
doi = {10.3390/min15030326},
author = {Ahmadi, Zahra and Nieto García, Fernando and Khormali, Farhad and Velilla Sánchez, Nicolás and Einali, Morteza and Maghsoudi, Abbas and Amini, Arash},
}