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Mineral Spectroscopy

Mineral Spectroscopy. Visible Infrared Raman Mössbauer NMR. Properties of Light. Light is conducted through materials on the valence electrons. Light travels more slowly in materials. Electrically conducting materials are opaque. Electromagnetic Spectrum.

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Mineral Spectroscopy

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  1. Mineral Spectroscopy Visible Infrared Raman Mössbauer NMR

  2. Properties of Light • Light is conducted through materials on the valence electrons. • Light travels more slowly in materials. • Electrically conducting materials are opaque

  3. Electromagnetic Spectrum Visible Light: 7700 - 3900Å

  4. Properties of Light • Light is conducted through materials on the valence electrons. • Light travels more slowly in materials. • Electrically conducting materials are opaque.

  5. Behavior of Light in Materials • Absorption (light is absorbed by materials) • Color (absorption is a function of wavelength) • Pleochroism (absorption is a function of direction) • Refraction (light travels slowly in some materials) • Dispersion (velocity is a function of wavelength) • Birefringence (velocity is a function of direction)

  6. Absorption • Light is attenuated on entering any material. • The attenuation is a function of distance. • I is intensity at some point t • I0 is initial intensity. • k is absorption coefficient in cm-1. • Lambert’s Law:

  7. Color • Absorption may be a function of wavelength. • Materials may appear colored in transmitted light

  8. Color • Absorption in the visible mainly due to electron transitions in d-orbitals or f-orbitals. • Color in minerals primarily due to presence of transition metals or rare earth elements.

  9. Visible and NIR spectra of Ametrine (quartz) Courtesy: George Rossman

  10. Ringwoodite is Blue • (g-Mg1.63Fe0.22 H0.4 Si0.95O4) • ~10 % of Fe present as ferric (Mössbauer)

  11. Pleochroism • Pleochroism is the variation of absorption with direction in a crystal. • Pleochroism is observed as a color change on rotation in plane-polarized light (not crossed polars). • Pleochroism only occurs in non-cubic crystals. • Pleochroism indicates the presence of transition metals (esp Fe, also Mn, Cr, V, etc). • Biotite,tourmaline, amphibole.

  12. Refraction and Reflection • When light strikes a polished surface of a material it is split into two rays. • One is reflected and the other refracted

  13. Infrared spectroscopy • Near IR 5000 - 13000cm-1 • orbital transitions • Mid-IR 2500 - 5000cm-1 • N-H and O-H bond vibrations • Far IR 500 - 2500 cm-1 • Cation-Oxygen bond vibrations • Structural phonons.

  14. FTIR Spectrometer

  15. Mid IR spectroscopy

  16. Mid IR spectroscopy

  17. Raman Spectroscopy • Looks at wavelength shifts in scattered light. • Shifts are in atomic vibrational part of spectrum • 0 - 5000cm-1. (same as mid to far IR) • Excitation is usually by a monochromatic source in the visible region (commonly a laser).

  18. Raman Spectroscopy

  19. Mössbauer Spectroscopy • Resonant Gamma Ray spectroscopy • Uses 57Fe gamma decay at 14.4 MeV • Source is 57Co • Source is accelerated mechanically to produce ultra-fine relativistic energy shifts • Absorption as a function of source velocity • Looks at electric field effects at nucleus due to d-orbital occupancy and perturbations from local coordination effects

  20. Mössbauer spectroscopy

  21. Mössbauer spectroscopy

  22. Mössbauer spectroscopy

  23. NMR Spectroscopy • Nuclear Magnetic Resonance • Similar to Mössbauer spectroscopy but many more nuclides • Radio frequency emission spectroscopy due to magnetic transitions in nucleus. • Solid samples are spun in a strong magnetic field (Magic Angle Spinning) • A RF field applied and turned off. • Sample emits RF

  24. NMR Spectroscopy

  25. NMR Spectroscopy

  26. NMR Spectroscopy

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