The First Occurrence of Asbestiform Magnesio-Riebeckite in Schists in the Frido Unit (Pollino Unesco Global Geopark, Southern Italy)

In this paper, new mineralogical and petrographical data of asbestiform Magnesio-riebeckite from ophiolite cropping out in the Pollino Unesco Global Geopark (southern Italy) are presented. Magnesio-riebeckite schists with HP-LT index mineral assemblage recorded metamorphic events in blueschist facies in the Frido Unit. Previous toxicological studies showed that asbestiform Magnesio-riebeckite species exhibited high carcinogenicity in previous intraperitoneal injection experiments with rats. The results have been obtained using different analytical techniques such as X-ray fluorescence (XRF), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and electron probe micro analysis (EPMA). Results show that all the samples contain fibrous Magnesio-riebeckite and/or prismatic, acicular crystals in aggregates. The concentration of elements in Magnesio-riebeckite crystals is: Na2O (4.12–6.26 wt%), MgO (8.22–10.87 wt%), FeO (19.07–23.81 wt%), SiO2 (52.05–56.06 wt%), CaO (1.12–4.53 wt%), Al2O3 (1.34–1.93 wt%), and MnO (0.10–0.34 wt%). Magnesio-riebeckite crystals are documented in the Pollino Unesco Global Geopark for the first time. For this reason, the aim of this paper is the characterization of Magnesio-riebeckite to improve the knowledge of this mineral in the studied area, because the release of fibers into the environment is dangerous for human health.

Using Natural Pozzolan, Cement and Lime for Stabilizing Soil in Earth Dams

The paper has focused on studying the ability of using natural pozzolan to combine lime and cement in process of stabilized soil, implementing experimental contents for on-site soil including: grain composition, plastic limit, plasticity index, mineral parts and other common mechanical properties, standard compaction. Followed by experiments for soil, cement and pozzolan stabilized soil mixtures, including standard compaction, compressive strength. A suitable model of physical experiments to simulate and prove lime, cement and pozzolan stabilized soil meets the criteria for making waterproofing materials for earth dams in the Central Highlands

Si-Disordering in MgAl2O4-Spinel at High P-T Conditions, with Implication to Si-Mg Disorder in Mg2SiO4-Ringwoodite

A series of Si-bearing MgAl2O4-spinels were synthesized at 1500-1650 °C and 3–6 GPa. These spinels had SiO2 contents up to ~1.03 wt%, and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+. Unpolarized Raman spectra were collected from polished single grains, and displayed a set of well-defined Raman peaks at ~610, 823, 856 and 968 cm-1 which had not been observed before. Aided with the Raman features of natural Si-free MgAl2O4-spinel, synthetic Si-free MgAl2O4-spinel, natural low quartz, synthetic coesite, synthetic stishovite and synthetic forsterite, we infer that these Raman peaks should belong to the SiO4 groups. The relations between the Raman intensities and SiO2 contents of the Si-bearing MgAl2O4-spinels suggest that at some P-T conditions some Si must adopt the M-site. Unlike the SiO4 groups with very intense Raman signals, the SiO6 groups are largely Raman-inactive. We have further found that the Si cations primarily appear on the T-site at P-T conditions ≤ ~3–4 GPa and 1500 °C, but attain a random distribution between the T-site and M-site at P-T conditions ≥ ~5–6 GPa and 1630–1650 °C. This Si-disordering process observed for the Si-bearing MgAl2O4-spinels hints that similar Si-disordering might happen to the (Mg,Fe)2SiO4-spinels (ringwoodite), the major phase in the lower part of the mantle transition zone of the Earth and the index mineral for the very strong shock stage experienced by extraterrestrial materials. The likely consequences have been explored.

Occurrence of chloritoid-bearing metapelitic rocks and their significance in the metamorphism of the Silgará Formation at the Central Santander Massif

We report here for the first time the occurrence of chloritoid in Mg-Al-rich metapelitic rocks of the Silgará Formation at the Central Santander Massif, which was metamorphosed up to the amphibolite facies. These rocks contain an unusual mineral assemblage such as quartz + biotite + muscovite + garnet + staurolite ± kyanite ± chloritoid, with minor plagioclase and K-feldspar, and Fe-Ti oxides as the main accessory phases. Associated carbonate rocks containing the mineral assemblage tremolite + calcite. Chloritoid occurs as porphyroblastic tablets in graphite-bearing metapelitic schists highly tectonized that can be associated to the influence of the major tectonic structures in the study area. The occurrence of chloritoid as an index mineral in metapelitic rocks of the Silgará Formation is attributed to a thermal event (associated to the emplacement of small granitic masses) overimposed on the regional metamorphism.