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Rock Forming Minerals
Published in Aurèle Parriaux, Geology, 2018
H.B. de Saussure named dolomite after D. Dolomieux, professor at the University of Grenoble, for his research on this mineral. Dolomite is the intermediate member of the solid solution between calcium carbonate and magnesium carbonate. Dolomite occurs as rhombohedral crystals. It is commonly found as a monomineralic rock either as a compact mass of microcrystals resembling fine limestone or as a poorly cohesive crystalline assemblage (saccharoidal dolomite). Like calcite, this carbonate has perfect rhombohedral cleavage. Colorless or whitish in color with a hint of pink or gray, its hardness ranges from 3.5 to 4 and it has a density of 2.85 · 103 kg/m3. Its luster is vitreous to pearly. In contrast to calcite, it reacts almost imperceptibly with dilute strong acids. But when it is reduced to powder, it reacts visibly to acid. Rock composed essentially of dolomite is called dolomite. Mixed with calcite, it produces dolomitic limestone. These rocks can make up entire rocky massifs, the most famous of which is the Dolomites on the border between Italy and Austria. Dolomitic rocks are a bit less susceptible to dissolution by water than limestones (Chaps. 7 and 13).
Rock Forming Minerals
Published in Aurèle Parriaux, Geology, 2018
H.B. de Saussure named dolomite after D. Dolomieux, professor at the University of Grenoble, for his research on this mineral. Dolomite is the intermediate member of the solid solution between calcium carbonate and magnesium carbonate. Dolomite occurs as rhombohedral crystals. It is commonly found as a monomineralic rock either as a compact mass of microcrystals resembling fine limestone or as a poorly cohesive crystalline assemblage (saccharoidal dolomite). Like calcite, this carbonate has perfect rhombohedral cleavage. Colorless or whitish in color with a hint of pink or gray, its hardness ranges from 3.5 to 4 and it has a density of 2.85 · 103 kg/m3. Its luster is vitreous to pearly. In contrast to calcite, it reacts almost imperceptibly with dilute strong acids. But when it is reduced to powder, it reacts visibly to acid. Rock composed essentially of dolomite is called dolomite. Mixed with calcite, it produces dolomitic limestone. These rocks can make up entire rocky massifs, the most famous of which is the Dolomites on the border between Italy and Austria. Dolomitic rocks are a bit less susceptible to dissolution by water than limestones (Chapts. 7 and 13).
Crystallization
Published in George A. Lane, Solar Heat Storage: Latent Heat Materials, 1983
Geometric considerations reveal that there are only 14 basic types of crystal lattice. On the basis of symmetry these are grouped into seven crystal systems. Cubic or isometric — the three crystal axes are all equal and at right angles to one another.Tetragonal — two crystal axes are equal, the third unequal. All axes are at right angles.Orthorhombic — the three crystal axes are unequal. All axes are at right angles.Trigonal or rhombohedral — the three crystal axes are equal, two are at right angles and the third is not. This is now treated in the U.S. as a subsystem of the hexagonal crystal system.Monoclinic — the three axes are unequal. Two axes are at right angles, the third is not.Triclinic or anorthic — the three axes are unequal, and none is at right angles to another.Hexagonal — three coplanar, equal axes are at 60° to each other, the fourth axis is unequal and at right angles to the three.
The effect of particle size on the structural, magnetic and electrical properties of La0.9Ba0.1MNO3 manganite samples
Published in Phase Transitions, 2019
Figure 1 shows the XRD patterns of the samples at room temperature. The XRD data is analyzed with Rietveld refinement. It is found that the samples are single phase, and there is a good agreement between the observed and calculated profiles. It is found that the samples crystallize in the rhombohedral structure with R-3c space group. Also, it can be seen from the XRD pattern of sample S2 that the (110), (111), (210), (211) peaks were split into two peaks (inset to Figure 1(b)), while such splitting is absent in the XRD pattern of sample S1, (inset of Figure 1(a)). This means that the sample S2 by the micrometer-sized particles has enhanced rhombohedral distortions with respect to sample S1 by the nanometer-sized particles [7–9]. On the other hand, the nanometer-sized crystals of La0.9Ba0.1MnO3 are characterized by better crystalline homogeneity, while the micrometer-sized sample is inhomogeneously disordered crystals.
Synthesis of CaCO3 nanocomposite from natural carbonate source and its effect on the inclusion of Eu3+ ions for photocatalytic activity
Published in Chemical Engineering Communications, 2023
Ramasamy Venkidasamy, Thenpandiyan Elumalai, Suresh Govindhasamy, Sathishpriya Tharmalingam, James Jebaseelan Samuel Emmanuel Rajan
A biomimetic route was used to synthesized nano CaCO3 (nC), various polymer mediated CaCO3, and various concentrations of Eu3+ anchored CaCO3 from a natural carbonate source (CaMg(CO3)2).The functional groups of the prepared samples were analyzed through FTIR. The confirmation of the rhombohedral structure and crystallite size of the samples was obtained by XRD analysis. The addition of polymers on the CaCO3 surface reduces the nucleation growth of the particle. The plane intensities of the Eu3+ anchored CaCO3/PEG samples decreased with an increase in the concentration of Eu3+ ions. It is due to the successful incorporation of Eu3+ ions into the Ca2+ lattice. The TG-DTA analysis exhibits high thermal stability, compared with the pioneer workers. The aggregated spherical and rhombohedral structures were observed through FESEM and HR-TEM analysis. The elemental composition and atomic ratio of the samples were confirmed by EDX analysis. Due to the impact of Eu3+ in CaCO3, the absorption and emission values of Eu3+ anchored CaCO3/PEG samples were red-shifted compared with nC. With increasing Eu3+ concentration, the direct and indirect band gap values increase slightly. Relative quantum yields were also calculated as 17%, 21%, and 19%. The photocatalytic analysis of the nCE1 sample exhibits good degradation efficiency (87%) against MB dye for 90 min, compared with nC and nCE4. These results show that the nCE1 material that was made is a good candidate for use in photocatalysis.