Moganite
Silica mineral, rare monoclinic polymorph of quartz
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Through Chemical formula, Silicon and Oxygen
Moganite has been mainly found in dry locales such as Gran Canaria and Lake Magadi. It has been reported from a variety of locations in Europe, India and the United States. Physically, it has a Mohs hardness of about 6, a dull luster, and a semitransparent gray color.
Structural information
The main infrared spectroscopy (IR) differences between moganite and α-quartz occur in the wavenumber region below 650 cm−1. Above this wavenumber, the frequencies of Si–O stretching vibrations of moganite are almost identical to those of quartz. Additional moganite bands were recorded near 165, 207, 296, 343, 419, 576, and 612 cm−1.
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Structural phase transition
Synchrotron X-ray powder diffraction data for moganite from 100 to 1,354 K (−173 to 1,081 °C) has revealed a reversible phase transition from space group I2/a to Imab at approximately 570 K (297 °C). The in-situ Fourier transform infrared spectroscopy shows that while the thermal responses of H2O and OH in moganite display similarities to agate, the spectra are not completely identical. Absorptions in the O–H stretching region reveal that the process of dehydration and dehydroxylation has multiple stages. Although hydrogen loss starts below 400–500 K (127–227 °C), hydrous species may well remain in moganite even at 1,060 K (790 °C).