Kiss Your Electron Goodbye: Ferrous Glass to Ferric Oxide

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Kiss Your Electron Goodbye Ferrous Glass to
Ferric Oxide

• Lecture 5
• PGL

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Glass

• Important component on the moon, Mercury,
  probably Mars
• Impact melt
• Pyroclastic
• Space weathering product

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Glass

• Only short range order
• Crystallographic sites exist, but only locally,
  no long range order
• Abundance of site geometry leads to broad bands

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Lunar Glass simulations

• Bell glasses were formed in very low oxygen
  environment, but not reducing
• Compositions designed to address lunar glass
  problems.

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Fe-free
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Glass spectral characteristics

• Beyond 800nm reflectance is strongly correlated
  with FeO
• TiFe shows a peak effect at shorter wavelengths,
  suggests a tife charge transfer
• Conventional wisdom extrapolates to shorter
  wavelenghts, but

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Lab to field glasses

• 15401 v. similar to Bell glasses
• 74420 (orange glass) contains some ilmenite
• 74001 is not glass, ilmenite spicules in a
  spheric shape (devitrified orange glass)

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Iron Oxides

• Oxidizing environments, esp. Earth and Mars
• Anhydrous--hematite, maghemite, magnetite
• Hydrous--goethite-lepidochrosite,limonite
• garbage bag of other Fe-oxides, mostly goethite

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Iron Oxides Hematite

• Hematite-Fe2O3, iron is ferric (Fe3), not
  ferrous (Fe2)
• Massive hematite is metal-like in appearance (k
  large), usual appearance is pigmentary, various
  shades of red
• Absorption coefficient is very high owing to
  intense metal-oxygen charge transfer bands, but
  strongly colored (absorptions largely in UV),
  giving rise to red streak in particles in the
  100-1000nm size (0.1-1 micron) range
• Common mineral in weathered basalts from
  ferromagnesian minerals

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Fine grained (pigmentary) hematites

• Steep dropoff in reflectance toward UV
• Strong crystal field bands superimposed near 650
  and 900 nm.

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Iron Oxides Maghemite

• Maghemite-Fe2O3, spinel structure, distinct from
  hematite
• Product of oxidation of magnetite and dehydration
  of ferrihydroxides

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Maghemite Spectrum

• Similar to hematite, but 650 nm feature weaker,
  feature near 1 micron at longer wavelengths

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Iron Oxides Goethite

• Goethite-FeOOH,
• Contains structural OH
• Slow oxidation of Fe2 minerals or slow
  hydrolysis of Fe3 minerals

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Goethite Spectra

• UV drop-off characteristic of Fe-oxide
• Substantially altered appearance of CF bands
  relative to hematite

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Iron Oxides Lepidichrosite

• Lepidochrosite-FeOOH polymorpth
• Contains structural OH
• Fast oxidation of Fe2 minerals or slow
  hydrolysis of Fe3 minerals

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Lepidochrosite Spectrum

• UV drop-off characteristic of Fe-oxide
• Substantially altered appearance of CF bands
  relative to hematite

Goethite
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Mars

• Red planet
• Red iron oxides

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Mars Bright Region Spectrum

• Steep red slope in visible/near IR
• No crystal field bands
• !

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Mars Bright Region Spectrum
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Mars Bright Region Spectrum
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Mars Bright Region Spectrum
Reducing the size of the hematite Particles
reduces the intensity Of the bands at same FeO
content
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Mars Bright Region Spectrum
Reducing the size of the hematite Particles
reduces the intensity Of the bands at same FeO
content
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Mars Bright Region Spectrum
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Mars Bright Region Spectrum
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Nanophase Hematite

• On Earth formed from weathering of basaltic glass
• Strange optical effects due to very fine grain
  size (particles only 10 unit cells in diameter)
• Probably coloring agent in Mars dust

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Temperature Dependent Spectral Effects

• Hematite and other oxides show color changes with
  temperature
• Due to slight variations in bond lengths and
  vibration with temperature

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Temperature Dependent Spectral Effects

• Fe-bearing silicates show spectacular temperature
  effects
• Due to slight variations in bond lengths and
  vibration with temperature

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Temperature Dependent Spectral Effects

• Fe-bearing silicates show spectacular temperature
  effects
• Due to slight variations in bond lengths and
  vibration with temperature

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Temperature Dependent Spectral Effects

• Slightly more complex rocks also show effects
• Eucrite

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Temperature Dependent Spectral Effects

• Slightly more complex rocks also show effects
• H5 chondrite (ol-pxn)

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Temperature Dependent Spectral Effects

• A-asteroids show evidence that low-T olivine is
  present
• Main belt asteroids are cold

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Temperature Dependent Spectral Effects
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Temperature Dependent Spectral Effects