Ricerc@Sapienza

Mineral evolution is concerned with the timing of mineral occurrences, such as the earliest reported occurrences in the geologic record. Minerals containing essential Li have not been reported from rocks older than ca. 3000 Ma, thus the lithian tourmaline (fluor-elbaite) and mica (lepidolite) assemblage from a pegmatite near Zishineni associated with the ca. 3000 Ma Sinceni Pluton presents unusual interest. Fluor-elbaite (0.75-0.98 F per formula unit) forms green crystals up to 50 trim long. Spindle stage measurements give omega = 1.652(1), epsilon = 1.627(1) (589.3 nm).

Tourmalines form the most important boron rock-forming minerals on Earth. They belong to the
cyclosilicates with a structure that may be regarded as a three-dimensional framework of octahedra ZO6
that encompass columns of structural “islands” made of XO9, YO6, BO3, and TO4 polyhedra. The overall
structure of tourmaline is a result of short-range and long-range constraints resulting, respectively on the
charge and size of ions. In this study, published data are reviewed and analyzed to achieve a synthesis

An Fe-rich fluor-elbaite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe- and Al-ordering over the octahedrally coordinated Y and Z sites. Overall, the experimental data (structural refinement, electron and ion microprobe, Mössbauer, infrared and optical absorption spectroscopy) show that thermal treatment of fluor-elbaite results in an increase of Fe contents at the Z site balanced by an increase of Al at the Y site.

A green tourmaline sample from the Tzarevskoye uranium–vanadium deposit, close to the Srednyaya Padma deposit, Lake Onega, Karelia Republic, Russia, has been found to be the second world-occurrence of Cr-rich vanadio-oxy-dravite in addition to the Pereval marble quarry, Sludyanka crystalline complex, Lake Baikal, Russia, type-locality. From the crystal-structure refinement and chemical analysis, the following empirical formula is proposed: X(Na0.96K0.02□0.02)Σ1.00 Y(V1.34Al0.68Mg0.93Cu2+0.02Zn0.01Ti0.01)Σ3.00 Z(Al3.19Cr1.36V0.03Mg1.42)Σ6.00(TSi6O18)(BBO3)3V(OH)3W[O0.60(OH)0.23F0.17]Σ1.00.

Tourmalines from the late-Variscan Arbus pluton (SWSardinia) and its metamorphic aureole were structurally
and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis,
Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the
magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic
system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes

An inclusive study of tourmaline, a well-known petrogenetic indicator, allowed the reconstruction of late-stage evolution of B-bearing Variscan granodioritic magmas in Sardinia batholith (Italy). Tourmaline samples from Mandrolisai igneous massif were chemically and structurally investigated by electron microprobe analysis, single-crystal X-ray diffraction, Mössbauer, infrared and optical absorption spectroscopy.