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Temperature dependence of reflectance spectra and color values of hematite by in situ, high-temperature visible micro-spectroscopy

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Published/Copyright: April 1, 2015
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American Mineralogist
From the journal American Mineralogist Volume 94 Issue 1

Abstract

We measured visible reflectance spectra and colors of hematite (α-Fe2O3) reagent powders and a natural feldspar grain containing dispersed hematite microcrystals from room temperature up to 800 °C using an in situ, high-temperature visible micro-spectrometer with dark field optics. The spectrum of room-temperature hematite powder is characterized by a nearly constant reflectivity in the range 400-550 nm, a shoulder near 620 nm, and a reflectivity maximum near 750 nm. The reflectance spectrum is similar to the diffuse reflectance spectra measured by a spectrophotometer and a conventional spectrometer with an integrating sphere. This result indicates that the dark field objective is suitable for measuring visible reflectance spectra of hematite powders with the visible micro-spectrometer. The reflectance of hematite powders in the longer wavelength region (>550 nm) decreases gradually with increasing temperature. The shoulder centered around 620 nm and the reflectance maximum near 750 nm also become indistinct at high temperatures. The calculated L* (dark-light), a* (red-green), and b* (blue-yellow) color values decrease with increasing temperature. This means that the red color of hematite becomes black with temperature increase. The calculated absorption intensities (Kubelka- Munk functions) suggest that this temperature dependence of the hematite powder-reflectance spectra can be mainly explained by a change in band gap absorption edges for a semiconductor (Urbach rule). The visible spectra and colors of a natural feldspar grain containing dispersed hematite microcrystals show a similar change with temperature, indicating that the temperature dependence can be observed under natural conditions at high temperatures, such as in volcanic eruptions.

Keywords : Visible micro-spectroscopy; dark field optics; hematite; visible reflectance spectra; L*a*b* color values; temperature dependence; Kubelka-Munk function
Received: 2007-9-5
Accepted: 2008-7-9
Published Online: 2015-4-1
Published in Print: 2009-1-1

© 2015 by Walter de Gruyter Berlin/Boston

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  1. Amorphous materials: Properties, structure, and durability. The viscosity of hydrous NaAlSi3O8 and granitic melts: Configurational entropy models
  2. Alteration mineralogy and the effect of acid-leaching on the Pb-isotope systematics of ocean-island basalts
  3. Color origin and heat evidence of paleontological bones: Case study of blue and gray bones from San Josecito Cave, Mexico
  4. Coexistence of pyroxenes jadeite, omphacite, and diopside/hedenbergite in an albite-omphacite rock from a serpentinite mélange in the Kurosegawa Zone of Central Kyushu, Japan
  5. Amphibole equilibria in mantle rocks: Determining values of mantle aH2O and implications for mantle H2O contents
  6. Experimental fluoridation of nanocrystalline apatite
  7. Dehydration dynamics of barrerite: An in situ synchrotron XRPD study
  8. Structural features in Tutton’s salts K2[M2+(H2O)6](SO4)2, with M2+ = Mg, Fe, Co, Ni, Cu, and Zn
  9. Incorporation of water in iron-free ringwoodite: A first-principles study
  10. Temperature dependence of reflectance spectra and color values of hematite by in situ, high-temperature visible micro-spectroscopy
  11. Lattice thermal expansion of zircon-type LuPO4 and LuVO4: A comparative study
  12. Solubility of H2O and CO2 in ultrapotassic melts at 1200 and 1250 °C and pressure from 50 to 500 MPa
  13. Multi-analytical approach to solve the puzzle of an allanite-subgroup mineral from Kesebol, Västra Götaland, Sweden
  14. Dislocation modeling in calcium silicate perovskite based on the Peierls-Nabarro model
  15. Molecular dynamics insight into the cointercalation of hexadecyltrimethyl-ammonium and acetate ions into smectites
  16. Adding further complexity to the polybasite structure: The role of Ag in the B layer of the -M2a2b2c polytype
  17. Structural position of H2O molecules and hydrogen bonding in anomalous 11 Å tobermorite
  18. Electronic structures of siderite (FeCO3) and rhodochrosite (MnCO3): Oxygen K-edge spectroscopy and hybrid density functional theory
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  20. The composition of KLB-1 peridotite
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https://doi.org/10.2138/am.2009.2779
Keywords for this article
Visible micro-spectroscopy; dark field optics; hematite; visible reflectance spectra; L*a*b* color values; temperature dependence; Kubelka-Munk function

Articles in the same Issue

  1. Amorphous materials: Properties, structure, and durability. The viscosity of hydrous NaAlSi3O8 and granitic melts: Configurational entropy models
  2. Alteration mineralogy and the effect of acid-leaching on the Pb-isotope systematics of ocean-island basalts
  3. Color origin and heat evidence of paleontological bones: Case study of blue and gray bones from San Josecito Cave, Mexico
  4. Coexistence of pyroxenes jadeite, omphacite, and diopside/hedenbergite in an albite-omphacite rock from a serpentinite mélange in the Kurosegawa Zone of Central Kyushu, Japan
  5. Amphibole equilibria in mantle rocks: Determining values of mantle aH2O and implications for mantle H2O contents
  6. Experimental fluoridation of nanocrystalline apatite
  7. Dehydration dynamics of barrerite: An in situ synchrotron XRPD study
  8. Structural features in Tutton’s salts K2[M2+(H2O)6](SO4)2, with M2+ = Mg, Fe, Co, Ni, Cu, and Zn
  9. Incorporation of water in iron-free ringwoodite: A first-principles study
  10. Temperature dependence of reflectance spectra and color values of hematite by in situ, high-temperature visible micro-spectroscopy
  11. Lattice thermal expansion of zircon-type LuPO4 and LuVO4: A comparative study
  12. Solubility of H2O and CO2 in ultrapotassic melts at 1200 and 1250 °C and pressure from 50 to 500 MPa
  13. Multi-analytical approach to solve the puzzle of an allanite-subgroup mineral from Kesebol, Västra Götaland, Sweden
  14. Dislocation modeling in calcium silicate perovskite based on the Peierls-Nabarro model
  15. Molecular dynamics insight into the cointercalation of hexadecyltrimethyl-ammonium and acetate ions into smectites
  16. Adding further complexity to the polybasite structure: The role of Ag in the B layer of the -M2a2b2c polytype
  17. Structural position of H2O molecules and hydrogen bonding in anomalous 11 Å tobermorite
  18. Electronic structures of siderite (FeCO3) and rhodochrosite (MnCO3): Oxygen K-edge spectroscopy and hybrid density functional theory
  19. Crystal growth and the fast reaction paradox: Mathematical resolution and implications for habit and compositional zoning
  20. The composition of KLB-1 peridotite
  21. Crystal chemistry of the magnetite-ulvöspinel series
  22. New insights into the crystal structure and crystal chemistry of the zeolite phillipsite
  23. Letter: Octahedral cation distribution in palygorskite
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