| Moganite | |
|---|---|
 | |
| General | |
| Category | Tectosilicates,quartzgroup |
| Formula | SiO2 |
| IMA symbol | Mog[1] |
| Strunz classification | 4.DA.20 |
| Dana classification | 75.01.04.02 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH–M symbol) |
| Space group | I2/a |
| Identification | |
| Color | Grey |
| Crystal habit | Massive |
| Mohs scale hardness | 6 |
| Luster | Earthy, dull |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.52 – 2.58 |
| Optical properties | Biaxial |
| Refractive index | nα = 1.524 nγ = 1.531 |
| References | [2][3][4] |
Moganite is atectosilicate mineral with thechemical formulaSiO2 (silicon dioxide) that was discovered in 1976. It was initially described as a new form of silica from specimens found in the Barranco de Medio Almud, in the municipality ofMogán on the island ofGran Canaria, in theCanary Islands (Spain),[5] receiving in a later work the name derived from this locality.[6] In 1994 the International Mineralogical Association decided to disapprove it as a valid mineral, since it was considered indistinguishable fromquartz.[7] Subsequent studies allowed the IMA to rectify it in 1999, accepting it as a mineral species.[8]It has the samechemical composition as quartz, but a differentcrystal structure.[4]
This mineral has been mainly found in dry locales such as Gran Canaria andLake Magadi.[9] It has been reported from a variety of locations in Europe, India and the United States.[3] Physically, it has aMohs hardness of about 6, a dull luster and appears as a semitransparent gray in color.
The maininfrared spectroscopy (IR) differences between moganite and α-quartz occur in thewavenumber 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.[10]
SynchrotronX-ray powder diffraction data for moganite from 100 to 1,354 K (−173 to 1,081 °C) has revealed a reversiblephase transition fromspace group I2/a to Imab at approximately 570 K (297 °C).[11] The in-situFourier transform infrared spectroscopy shows that while the thermal responses of H2O and OH in moganite display similarities toagate, the spectra are not completely identical. Absorptions in the O–H stretching region reveal thatdehydration anddehydroxylation is a multistage process. 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).[12]
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| Cryptocrystalline | |||||||||
| Amorphous | |||||||||
| Miscellaneous | |||||||||
| Notable varieties |
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