Olivine Group A 22 Si O 4 Olivine

Olivine Group (A 2+)2 Si. O 4

Olivine End-Members • • • Forsterite Mg 2 Si. O 4 Fayalite Fe 2 Si. O 4 Tephroite Mn 2 Si. O 4 Liebenbergite Ni 2 Si. O 4 Co-olivine Co 2 Si. O 4 Ca-olivine Ca 2 Si. O 4 Monticellite Ca. Mg. Si. O 4 Kirschsteinite Ca. Fe. Si. O 4 Glaucochroite Ca. Mn. Si. O 4

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

Gabbro, Skaergaard

Olivine in Gabbro

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 • M 1 – Pt sym = -1 @ (0, 0, 0) • M 2 – Pt symm = m @ ( x, y, 1/4) • Si – Pt symm = m @ ( x, y, 1/4) • O 1, O 2 – Pt symm = m @ ( x, y, 1/4) • O 3 – Pt symm = 1 @ ( x, y, z)

Olivine M 1 • • • M 1 is at origin Smaller M site More distorted in angles Less distorted in distances Mg, Fe olivines are disordered Ni prefers M 1

Olivine M 2 • • • 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 M 2

Olivine Chemistry • Mantle olivines are Fo 94 - Fo 86 • Minor elements are divalent cations and H – Ni (M 1) up to 0. 1 wt % Ni. O – Mn (M 2) up to 0. 1 wt% Mn. O – Ca (M 2) up to 0. 1 wt% Ca. O • Very low in mono- and tri-valent cations • Minor P in meteoritic Olivine

Olivine Stability b a g

Olivine Thermal Expansion

Olivine Compression

Hydration of Olivine • Unit Cell parameters and complete crystal structure refinements. (Hydrous olivine composition) – Fo 100: Pure Synthetic Forsterite – SC: San Carlos olivine (Fo 91) – CS San Carlos + H 2 O 1 GPa @ 1100º – SS 0001: 12 GPa @ 1200 ºC (Wadsleyite + Olivine) – SS 0003: 12 GPa @ 1400 ºC (Olivine only) – SS 0004: 12 GPa @ 1600 ºC (Olivine only)

SC CS SS 0004 SS 0003 SS 0001 Fo 100

SC CS SS 0004 SS 0003 SS 0001 Fo 100