Occurrence and distribution of "moganite" in agate/chalcedony: a combined micro-Raman, Rietveld, and cathodoluminescence study

Article Abstract:

The spatial distribution of moganite in microcrystalline silica samples, predominantly in rhythmically zoned agates, were investigated to ascertain the formation of these samples. The moganite content in microcrystalline SiO2 samples measured by Raman spectroscopy was found to be considerably higher than the moganite content measured by X-ray diffractometry. The difference is explained by the presence of moganite nanocrystals, nano-range moganite lamellae and single Brazil-law twin-planes that are detected by vibrational spectroscopy but not by X-ray diffractometry.

Silica, Raman spectroscopy, Agates, Silicon dioxide, Chalcedony, Cathodoluminescence

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Infrared spectroscopic investigations of the calcite-rhodochrosite and parts of the calcite-magnesite mineral series

Article Abstract:

Infrared spectroscopic analysis of calcite-rhodochrosite and calcite-magnesite minerals was undertaken to measure frequency shifts in the vibrational bands v2 and v4 of the carbonate group. Results indicate that this shift in vibrational bands is a function of the chemical composition. The shift was found to result from cationic substitution and that it was dependent on the radius and the mass of the substituting cation. A model explaining this shift in a system composed of calcium carbonate, manganese carbonate and magnesium carbonate is presented.

Models, Manganese, Manganese (Metal), Carbonates, Vibrational spectra, Molecular spectra, Magnesite

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High-pressure behaviour and equation of state of calcite, CaCO3

Article Abstract:

A study was conducted to analyze the high-pressure response of the cell parameters of calcite, CaCO3. Single crystal X-ray diffraction was utilized to carry out the analysis. Data on the anisotropy of compression in calcite was determined. The unit cell parameters were refined from 0 to 1.435 GPa. Results indicated similarities between the pressure response of rhombohedral calcite and rhombohedral carbonates.

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