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Olivine Group

Olivine Group

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Olivine Group

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  1. Olivine Group (A2+)2SiO4

  2. Olivine End-Members • Forsterite Mg2SiO4 • Fayalite Fe2SiO4 • Tephroite Mn2SiO4 • Liebenbergite Ni2SiO4 • Co-olivine Co2SiO4 • Ca-olivine Ca2SiO4 • Monticellite CaMgSiO4 • Kirschsteinite CaFeSiO4 • Glaucochroite CaMnSiO4

  3. Olivine Occurrences • Forsterite - Fayalite • Fo90 Olivine is major mineral of upper mantle • Minor phase in basalt and gabbro • Fayalite is secondary in silicic volcanics • Monticellite accessory in mantle nudules • Tephroite and glaucochroite • silicic volcanics and Mn skarns • Liebenbergite secondary in Ni deposits

  4. Olivine Nodules, San Carlos

  5. Gabbro, Skaergaard

  6. Olivine in Gabbro

  7. Olivine Structure

  8. Olivine Structure • Orthorhombic Pbnm • a = 4.7 - 5.1Å • b = 10.1 - 11.2Å • c = 5.9 - 7.8Å • Z = 4

  9. Olivine Structure • M1 • Pt sym = -1 @ (0, 0, 0) • M2 • Pt symm = m @ ( x, y, 1/4) • Si • Pt symm = m @ ( x, y, 1/4) • O1, O2 • Pt symm = m @ ( x, y, 1/4) • O3 • Pt symm = 1 @ ( x, y, z)

  10. Olivine M1 • M1 is at origin • Smaller M site • More distorted in angles • Less distorted in distances • Mg, Fe olivines are disordered • Ni prefers M1

  11. Olivine M2 • On mirror at (x, y, 1/4) • Larger M site • Less distorted in angles • More distorted in distances • Mg, Fe olivines are disordered • Ca, Mn prefer M2

  12. Olivine Chemistry • Mantle olivines are Fo94 - Fo86 • Minor elements are divalent cations and H • Ni (M1) up to 0.1 wt % NiO • Mn (M2) up to 0.1 wt% MnO • Ca (M2) up to 0.1 wt% CaO • Very low in mono- and tri-valent cations • Minor P in meteoritic Olivine

  13. Olivine Stability b g a

  14. Olivine Thermal Expansion

  15. Olivine Compression

  16. Hydration of Olivine • Unit Cell parameters and complete crystal structure refinements. (Hydrous olivine composition) • Fo 100: Pure Synthetic Forsterite • SC: San Carlos olivine (Fo91) • CS San Carlos + H2O 1 GPa @ 1100º • SS0001: 12 GPa @ 1200 ºC (Wadsleyite + Olivine) • SS0003: 12 GPa @ 1400 ºC (Olivine only) • SS0004: 12 GPa @ 1600 ºC (Olivine only)

  17. SC CS SS0004 SS0003 SS0001 Fo100

  18. SC CS SS0004 SS0003 SS0001 Fo100