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Calcite crystals were nucleated and grown from supersaturated aqueous solutions in the presence of variable concentrations of lithium. The diagram of supersaturation vs [Li+]/[Ca2+] concentration ratio (“morphodrome”) shows a continuous habit variation, from the dominant {011̄1} rhombohedron (at low [Li+]/[Ca2+] ratio) to the dominant {0001} form (at high [Li+]/[Ca2+] ratio). The morphological change is interpreted in terms of two-dimensional layers having the structure of the monoclinic Li2CO3 crystal which are epitaxially adsorbed on the restructured {0001} form of calcite. Hence, even if {0001} is a K form (in the sense of Hartman-Perdok), the corresponding surface behaves like a F form, growing layer by layer from low to high supersaturation values.

The identification of syngenetic inclusions in diamond (i.e. inclusions of minerals that crystallized at the same time and by the same genesis as their host) has long been of paramount importance in diamond studies. However, the widespread assumption that many or most inclusions in diamonds are syngenetic is based on qualitative morphological criteria and few direct measurements. In order to provide statistically significant information on inclusion–host genetic relations for at least one kimberlite, we have determined the crystallographic orientations of 43 olivine inclusions with diamond-imposed morphology, a feature generally interpreted to indicate syngenesis, in 20 diamonds from the Udachnaya kimberlite (Siberia). Our unprecedented large data set indicates no overall preferred orientation of these olivines in diamond. However, multiple inclusions within a single diamond frequently exhibit similar orientations, implying that they were derived from original single monocrystals. Therefore, regardless of the possible chemical re-equilibration during diamond-forming processes, at least some of the olivines may have existed prior to the diamond (i.e. they are protogenetic). Our results imply that a diamond-imposed morphology alone cannot be considered as unequivocal proof of syngenicity of mineral inclusions in diamonds

The structures of the (100), octopolar (111) Na-terminated [(111)Na], and (111) Cl-terminated [(111)Cl] surfaces of halite (NaCl) were determined by means of ab initio quantum mechanical calculations (density functional theory, DFT). The (111) surfaces show higher surface relaxation with respect to the (100) surface. The surface energies (γ) at T = 0 K for relaxed and unrelaxed (100) and (111) faces were determined at DFT level. The values of the surface energy for the relaxed faces are γ(100) = 160, γ(111)Cl = 390 and γ(111)Na = 405 erg/cm2; therefore, the stability order of relaxed surfaces reads: (100) < (111)Cl < (111)Na. For the unrelaxed faces, the surface energies are higher: γ(100) = 161, γ(111)Cl = 552 and γ(111)Na = 551 erg/cm2.To check if the octopolar (111) faces can belong to the equilibrium morphology of the crystal/vapor system, the relaxed surface energies at T > 0 K were calculated by considering both the vibrational motion of atoms and the surface configurational entropy. From these calculations it resulted that the octopolar (111)Na and (111)Cl faces cannot belong to the equilibrium morphology. Octopolar reconstruction and both surface vibrational and configurational entropy then allow us to explain why the {111} NaCl form cannot enter the equilibrium shape of the crystal.

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This study focuses on the occurrence and distribution of cyanobacterial toxins from 1989 to 2006 in several Italian lakes of different characteristics and human uses, the latter including drinking water abstraction and recreation. Phytoplankton and LC/MS/MS toxin analyses were performed on surface water samples collected from 28 lakes. The most widespread species associated with toxin production belonged to the genera Microcystis, Planktothrix and Anabaena. Extracellular concentrations varied from non-detectable values up to 226.16 ng/mL for microcystins (sum of all variants), to 126 ng/mL for total cylindrospermopsin, and to 100 mg/g (dry weight) for anatoxin-a. The toxin concentrations in the lake waters did not always correlate with the cyanobacteria cell densities. This implies a need for control studies including toxin detection in water together with microscopic cell evaluations, in order to avoid possible toxin underestimates

Ab initio calculations of thermo-elastic properties of beryl (Al 4 Be 6 Si 12 O 36 ) have been carried out at the hybrid HF/DFT level, by using the B3LYP and WC1LYP Hamiltonians. Static geometries and vibrational frequencies were calculated at different values of the unit cell volume, to get static pressure and mode-γ Grüneisen's parameters. Zero point and thermal pressures were calculated by following a standard statistical-thermodynamic approach, within the limit of the quasiharmonic approximation, and added to the static pressure at each volume, to get the total pressure (P) as a function of both temperature (T) and cell volume (V). The resulting P(V,T) curves were fitted by appropriate EoS', to get bulk modulus (K 0 ) and its derivative (K'), at different temperatures. The calculation successfully reproduced the available experimental data concerning compressibility at room temperature (the WC1LYP Hamiltonian provided K 0 and K' values of 180.2Gpa and 4.0, respectively), and the low values observed for the thermal expansion coefficient. A zone-centre soft mode 𝑃6 𝑚𝑐𝑐 ⁄ → 𝑃1 ̅ phase transition was predicted to occur at a pressure of about 14 GPa; the reduction of the frequency of the soft vibrational mode, as the pressure is increased, and the similar behaviour of the majority of the low frequency modes, provided an explanation of the thermal behaviour of the crystal, which is consistent with the RUM model (Rigid Unit Model;Dove et al., 1995), where the negative contribution to thermal expansion is ascribed to a geometric effect connected to the tilting of rigid polyhedra in framework silicates.

The “Four Twin Laws of Calcite”, expressed by their twin planes (10.4, 01.8, 01.2 and 0.01, hexagonal frame) have been investigated in order to assess the structure of the interfaces between twinned individuals. Athermal twinning and adhesion energies were evaluated by calculations using empirical potential functions: the relaxed interfaces were modeled to minimize the surface energy. To this end, different configurations of the twin interfaces have been considered when surface reconstructions were needed to cancel out the surface dipole moment, which is intrinsic to the ideal interfaces of both the (00.1) and (01.2) twins. Calculation shows that (i) the (00.1) twin law is the most likely to occur, and (ii) the minimum of the twinning energy is obtained if the twin operation is a diad axis perpendicular to the (00.1) interface. Finally, it has been demonstrated that the (00.1) twins are the only ones that can be generated by a 2D heterogeneous nucleation mechanism, while the 3D (either homogeneous or heterogeneous) nucleation is the dominating mechanism for the other twins.