Moganite
| Moganite | |
|---|---|
 | |
| General | |
| Category | Tectosilicate,quartzgroup |
| Formula (repeating unit) | 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 scalehardness | 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] |
Moganiteis anoxide mineralwith 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 ofMogánon 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 from quartz.[7]Subsequent studies allowed the IMA to rectify it in 1999, accepting it as a mineral species.[8] It has the samechemical compositionas 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 hardnessof about 6, a dull luster and appears as a semitransparent gray in color.
Structural information[edit]
The maininfrared spectroscopy(IR) differences between moganite and α-quartz occur in thewavenumberregion 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]
Structural phase transition[edit]
SynchrotronX-ray powder diffractiondata for moganite from 100 to 1,354 K (−173 to 1,081 °C) has revealed a reversiblephase transitionfromspace groupI2/a to Imab at approximately 570 K (297 °C).[11] The in-situFourier transform infrared spectroscopyshows 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 thatdehydrationanddehydroxylationis 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]
References[edit]
- ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
- ^"Mineralienatlas Lexicon – Mogánite".Mineralienatlas.Retrieved13 August2023.
- ^abRalph, Jolyon; Ralph, Ida (2007)."Moganite: Moganite Mineral Information and Data".MinDat.Retrieved1 August2007.
- ^ab"Webmineral data".
- ^Flörque, O.W.; Jones, J.B.; Schmincke, H.U. (1976). "A new microcrystalline silica from Gran Canaria".Zeitschrift für Kristallographie.143:156–165.
- ^Flörque, O.W.; Flörque, U.; Giese, U. (1984). "Moganite, a new microcristaline silica-mineral".Neues Jahrbuch für Mineralogie (Abhandlungen).149:325–336.
- ^Origlieri, M., 1994. "Moganite: a New Mineral – Not!"Lithosphere.Aug. 2007http://geopress.rbnet.net/moganite.htm
- ^Grice, Joel D.; Ferraris, Giovanni (2000). "New minerals approved in 1999 by the commission on new minerals and mineral names, International Mineralogical Association".The Canadian Mineralogist.38(1): 245–250.Bibcode:2000CaMin..38..245G.doi:10.2113/gscanmin.38.1.245.
- ^Heaney, Peter J.; Post, Jeffrey E. (1992). "The Widespread Distribution of a Novel Silica Polymorph in Microcrystalline Quartz Varieties".Science.255(5043): 441–443.Bibcode:1992Sci...255..441H.doi:10.1126/science.255.5043.441.PMID17842895.S2CID32497622.
- ^Zhang, Ming; Moxon, Terry (2014). "Infrared absorption spectroscopy of SiO2-moganite ".American Mineralogist.99(4): 671–680.Bibcode:2014AmMin..99..671Z.doi:10.2138/am.2014.4589.S2CID56255006.
- ^Heaney, Peter J.; Post, Jeffrey E. (2001). "Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at ~570 K".American Mineralogist.86(11–12): 1358–1366.Bibcode:2001AmMin..86.1358H.doi:10.2138/am-2001-11-1204.S2CID6093768.
- ^Zhang, Ming; Moxon, Terry (2012). "In situ infrared spectroscopic studies of OH, H2O and CO2in moganite at high temperatures ".European Journal of Mineralogy.24(1): 123–131.Bibcode:2012EJMin..24..123Z.doi:10.1127/0935-1221/2011/0023-2165.
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