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Iridescent Iron Oxides

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Udgivet i:Minerals vol. 15, no. 2 (2025), p. 108
Hovedforfatter: Rossman, George R
Andre forfattere: Ma, Chi
Udgivet:
MDPI AG
Fag:
X ray powder diffraction
Nanocrystals
Raman spectra
Iron oxides
Spectra
Electrons
Image resolution
Aluminum
Phosphorus
Haematite
Goethite
Protective coatings
Thin films
Crystals
Color vision
Infrared spectra
Infrared spectroscopy
Electron backscatter diffraction
Electron diffraction
Phosphates
Electron imaging
Arsenic
Raman spectroscopy
Hematite
Aluminium
Diffraction patterns
Morphology
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Resumen:Iridescent iron oxides known as rainbow hematite and turgite are found in a variety of localities worldwide and display a variety of beautiful interference colors. Usually, there is a thin layer of nanocrystals containing aluminum and phosphorous coats, such as with hematite, although one example of aluminum with arsenic is presented. Infrared spectra of samples with thicker layers of these nanocrystals show absorption in the phosphate region. The thin films that range from tens to hundreds of nanometers thick are believed to cause the color. High-resolution secondary electron imaging shows that the thin film consists of nanocrystals arranged in three directions (120° apart). The rod-shaped crystals have a width from 5 to 35 nm and display the same morphology on all samples, irrespective of if they contain phosphorus or arsenic. The minute crystals have failed to produce either an X-ray powder diffraction pattern, an electron back-scatter diffraction pattern in SEM, or an electron diffraction ring pattern under TEM. Raman spectra are dominated by hematite features. Infrared ATR spectra of the bulk material show mostly hematite with occasional minor amounts of goethite and phosphate.
ISSN:2075-163X
DOI:10.3390/min15020108
Fuente:ABI/INFORM Global