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This study investigates the capability of the Southeast Mesohellenic Trough (SE MHT) sandstone formations to serve as a potential reservoir for CO2 storage in response to the emerging climate change issues by promoting environmentally friendly mineral sequestration applications. Sandstone samples, for the first time, were evaluated for their petrographic characteristics, mineral chemistry, geochemical properties, as well as their petrophysical and gas adsorption properties through tests. The sandstones were tested and classified into distinct groups. The most promising site to be considered for pilot CO2 storage testing is the Pentalofos Formation locality since its sandstones display specific mineral phases with the proper modal composition to conceivably react with injected CO2, leading to the development of newly formed and stable secondary mineral phases. The gas adsorption results are also more encouraging for sandstones from this sedimentary formation. All the measured UCS (uniaxial compressive strength), Ei (bending stiffness), and ν (Poisson's ratio) results are above those dictated by international standards to perform CO2 storage practices safely. Furthermore, the specified targeted locality from the Pentalofos Formation holds the geological advantage of being overlaid by an impermeable cap-rock formation, making it suitable for deploying CO2 mineralization practices. The demarcated area could permanently store a calculated amount of ~50 × 105 tons of CO2 within the geological reservoir by reacting with the specified mineral phases, as specified through the proposed petrographic PrP index (potential reactive phases). [ABSTRACT FROM AUTHOR]

Small grains, approximately 15 µm in size, of a Ni-phosphide, have been discovered in two chromite deposits associated with altered mantle peridotite: (i) in Bakanov Kluch, Alapaesk ophiolite, Russia and (ii) in Agios Dimitrios, Gerakini-Ormylia ophiolite, Greece. On the basis of the chromite composition, both the Bakanov Kluch and the Agios Dimitrios chromitites are classified as Cr-rich chromitites with a boninitic affinity. Under reflected-light optical microscope, the Ni-phosphides are yellow in colour and isotropic. Their calculated stoichiometry, based on the average of 20 electron microprobe analyses, approaches the ideal formula (Ni,Fe)5P. One essential condition for the formation of terrestrial minerals in the Ni-Fe-P system is the presence of a highly reducing local geochemical environment. Serpentinization of oceanic peridotites produces reducing fluids containing dissolved H2 resulting from the reduction of H2O. Therefore, we suggest that the (Ni,Fe)5P from the Alapaevsk and Gerakini-Ormylia were very likely formed after the precipitation of the host chromitites during the serpentinization process at low temperatures. Nickel may have been released during the alteration of olivine and phosphorous may represent an alteration product of apatite. The (Ni,Fe)5P grains analyzed in the present work contain the highest value of Ni and they are characterized by the highest Ni to P ratio reported so far from similar minerals. Their stoichiometry indicates that the (Ni,Fe)5P grains found in the Alapaevsk and Gerakini-Ormylia chromitites represent a new mineral species. However, their small size prevents the acquisition of crystallographic data to support this assumption. [ABSTRACT FROM AUTHOR]