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Siliceous concretions (nodules), from two different geological settings—the Apulian platform margins in Kefalonia island, and the Ionian Basin in Ithaca, Atokos, and Kastos islands—have been studied both in the field and in the laboratory. Nodule cuttings are mainly characterized by the development of a core, around which a ring (rim) has been formed. Mineralogical study, using X-ray powder diffraction (XRPD) analysis, showed that the rim is usually richer in moganite than the core. Homogeneous concretions, without discernible inner core and outer ring, were observed generally in both settings. Mineralogical analysis of the selected siliceous concretions from Kefalonia island showed the presence mostly of quartz and moganite, while calcite either was absent or participated in a few samples in minor/trace abundances. Moganite was generally abundant in all the samples from Kefalonia island. Concretions from the Ionian Basin showed a variation in the quartz, moganite, and calcite contents. Mineralogical differences were recognized both between the different studied geodynamic settings and internally in the same setting, but with different stages of development. The above-mentioned differential diagenesis on nodules evolution could be related to the presence and/or abundance of stylolites, later fluid flows, restrictions from one area to another due to synchronous fault activity, and the composition of substances dissolved in fluids. Moreover, the development of concretions produced secondary fractures in the surrounding area of the nodule-bearing rocks.

This paper aims to study the chromitites, as well as their host rocks (meta-peridotites, meta-dunites and serpentinites) of the ophiolite complex of Mount Tsiknias, in Tinos Island. Recognition of their mineralogy and their textural features was carried out through detailed petrographic study. The mineral chemistry analysis contributed to the evaluation of the analyzed chromites, the chemical composition of which provides important information about the petrogenetic evolution of the chromitite ores. The chromites were in equilibrium with boninite melts derived from Supra-Subduction Zone, e.g., a depleted mantle wedge. In the binary classification diagram for spinels, the Tinos samples extend in the fields of Mg-chromite and chromite sensu strictu. In the TiO2 vs Al2O3 diagram, the chromites plot in the field of Supra-Subduction Zone (SSZ) peridotites and partly overlap the field of chromites in Back-Arc Basalts (BABB), however the same samples plot in the field of chromite of boninites. In the Al2O3 vs Cr2O3 diagram both groups of Tinos chromites plot in the field/extremity of "mantle chromites".

The study of microbial mats in extreme environments is of high scientific interest from geological, ecological, and geomicrobiological aspects. These mats represent multilayer bio-structures where each taxonomic group dominates a specific vertical layering distribution resulting from its growth and metabolic activity. In the present study, microbial mats in a hot spring environment from Aedipsos (Euboea Island, Greece) resulting in the creation of thermogenic travertine, were studied through an interdisciplinary approach. The mineralogical composition was determined by optical microscopy, XRD, and SEM-EDS microanalysis, and the identification of Cyanobacteria was made primarily on morphological characteristics. The main mineral phase in the studied samples is calcite and, to a less extent, aragonite, with several trace elements in the mineral-chemistry composition, i.e., up to 1.93 wt. % MgO, up to 0.52 wt. % SrO, up to 0.44 wt. % Na2O, up to 0.17 wt. % K2O, and up to 3.99 wt. % SO3. The dominant facies are lamination and shrubs, which are the most common among the facies of thermogenic travertines of the area. Several layers were identified, (i) a top mainly abiotic layer consisting of calcium carbonate micritic crystals, (ii) a second biotic layer–the Cyanobacteria layer, dominated by the species Leptolyngbya perforans, (iii) a third biotic layer where Leptolyngbya perforans, Chloroflexus and other bacteria occur, and (iv) a deeper abiotic part with several layers where no photosynthetic microorganisms occur. In the upper layers, nineteen (19) species of Cyanobacteria were identified, classified in the orders Chroococcales (37%), Synechococcales (31%), Oscillatoriales (16%), and Spirulinales (6%). Among the identified Cyanobacteria, there are typical thermophilic and limestone substrate species. These Cyanobacteria are found to participate in the biomineralization and biologically-influenced processes, i.e., (i) filamentous Cyanobacteria are trapping calcium carbonate crystals, and diatoms, (ii) extracellular polymeric substances (EPS) create crystal retention lattice contributing to the biomineralization process, and (iii) filamentous sheaths of Cyanobacteria are calcified, resulting in the creation of calcium carbonate tubes.

This paper describes a study case of the Science and Technology Museum “Pedagogical Competence Programme” for students of the Department of Geology. It highlights an experimental approach of the museum for designing museum educational programmes with students. The museum succeeded from one side to develop a new program to offer to schools using participatory design and from the other to offer university students pedagogical experience through innovative, non-formal educational programmes, new ways to approach school students at all levels, cultivate their special skills, and enhance their knowledge, in order to familiarise them with the popularisation of science.