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Olivine Group Olivine Group 2+ (A )2SiO4 Olivine End-Members • Forsterite Mg2SiO4 • Fayalite Fe2SiO4 • Tephroite Mn2SiO4 • Liebenbergite Ni2SiO4 • Co-olivine Co2SiO4 • Ca-olivine Ca2SiO4 • Monticellite CaMgSiO4 • Kirschsteinite CaFeSiO4 • Glaucochroite CaMnSiO4 1 Olivine Occurrences • Forsterite - Fayalite – Fo 90 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 Olivine Nodules, San Carlos 2 Gabbro, Skaergaard Olivine in Gabbro 3 Olivine Structure Olivine Structure • Orthorhombic Pbnm • a = 4.7 - 5.1Å • b = 10.1 - 11.2Å • c = 5.9 - 7.8Å • Z = 4 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) 4 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 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 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 5 Olivine Stability b g a Olivine Thermal Expansion End-Member Forsterite Fayalite Liebenbergite Monticellite Glaucochroite Chrysoberyl Formula Mg2SiO4 Fe 2SiO4 Ni 2SiO4 CaMg 0.93 Fe 0.07 SiO4 Ca0.98 Mn0.87 Mg0.10SiO4 Al 2BeO4 Sample Synthetic Synthetic Synthetic Natural Natural Natural T range 23-1600ºC 20-900ºC 25-900ºC 25-795ºC 25-800ºC 25-690ºC Unit cell aV (x 10-5 K-1) 4.36 3.19 3.44 2.97 3.17 2.39 aa (x 10 -5 K-1) 1.12 0.99 1.19 1.01 1.05 0.74 ab (x 10-5 K-1) 1.67 0.95 1.11 0.99 1.00 0.85 ac (x 10 -5 K-1) 1.46 1.19 1.12 1.13 1.09 0.83 Polyhedral Volumes (x 10-5 K-1) M1 4.32 2.88 4.19 4.68 4.55 2.25 M2 5.07 4.51 3.68 3.62 4.01 3.89 T 0 -1.17 0.36 -1.23 -2.13 2.57 NPV 4.40 3.37 3.33 3.20 2.81 1.99 Reference Takeuchi et al. Smyth (1975) Lager & Meagher Lager & Meagher Lager & Meagher Hazen and Finger (1984) (1978) (1978) (1978) (1987) Olivine Compression End-member Forsterite Forsterite Fayalite Fayalite Monticellite Chrysoberyl Formula Mg 2SiO4 Mg 2SiO4 Fe2SiO4 Fe 1..94Mn 0.11Mg 0.04SiO4 Ca0.99 Mg 0.91 Fe0.09 SiO4 Al2BeO 4 LiScSiO4 Sample Synthetic Synthetic Synthetic Natural Natural Natural synthetic Pmax (GPa) 5.0 14.9 4.2 14.0 6.2 6.25 5.6 K T0 (GPa) 132 123 113 132 113 242 118 K’ 4.0 (fixed) 4.3 4 (fixed) 4 (fixed) 4 (fixed) 4 (fixed) 4 (fixed) Axial Compressions (10-3 GPa -1) ba 1.6 1.5 0.8 1.2 1.96 1.09 2.70 bb 4.3 2.8 5.8 4.0 3.62 1.47 2.80 bc 0.8 2.7 1.4 1.3 2.05 1.32 2.61 Site bulk moduli (GPa) M1 120 140 130 150 180 84 M2 100 130 130 110 300 204 Si >550 190 >500 >400 >300 300 315 Reference Hazen (1976) Kudoh & Hazen (1977) Kudoh & Takeda (1986) Sharp et al. (1987) Hazen (1987) Hazen et al. Takeuchi (1985) (1996) 6 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 + H2 O 1 GPa @ 1100º – SS0001: 12 GPa @ 1200 ºC (Wadsleyite + Olivine) – SS0003: 12 GPa @ 1400 ºC (Olivine only) – SS0004: 12 GPa @ 1600 ºC (Olivine only) Cell Volume vs Fo# 292.5 SC 292 CS 291.5 SS0004 SS0003 291 SS0001 290.5 Unit Cell Volume (Å^3) Fo100 290 90 92 94 96 98 100 Fo# M2 Vol vs Mg Occupancy 12.52 SC 12.51 12.5 CS 12.49 12.48 SS0004 SS0003 12.47 12.46 M2 Volume (Å^3) SS0001 12.45 12.44 12.43 Fo100 90 92 94 96 98 100 Fo # 7.
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