Olivine Group

(A2+)2SiO4

Olivine End-Members• Forsterite Mg2SiO4

• Fayalite Fe2SiO4

• Tephroite Mn2SiO4

• Liebenbergite Ni2SiO4

• Co-olivine Co2SiO4

• Ca-olivine Ca2SiO4

• Monticellite CaMgSiO4

• Kirschsteinite CaFeSiO4

• Glaucochroite CaMnSiO4

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

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• 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)

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

Olivine Stability

End-Member Forsterite Fayalite Liebenbergite Monticellite Glaucochroite ChrysoberylFormula Mg2SiO4 Fe2SiO4 Ni2SiO4 CaMg0.93Fe0.07SiO4 Ca0.98Mn0.87Mg0.10SiO4 Al2BeO4

Sample Synthetic Synthetic Synthetic Natural Natural NaturalT range 23-1600ºC 20-900ºC 25-900ºC 25-795ºC 25-800ºC 25-690ºCUnit cellV (x 10-5 K-1) 4.36 3.19 3.44 2.97 3.17 2.39a (x 10-5 K-1) 1.12 0.99 1.19 1.01 1.05 0.74b (x 10-5 K-1) 1.67 0.95 1.11 0.99 1.00 0.85c (x 10-5 K-1) 1.46 1.19 1.12 1.13 1.09 0.83Polyhedral Volumes (x 10-5 K-1)M1 4.32 2.88 4.19 4.68 4.55 2.25M2 5.07 4.51 3.68 3.62 4.01 3.89T 0 -1.17 0.36 -1.23 -2.13 2.57NPV 4.40 3.37 3.33 3.20 2.81 1.99Reference Takeuchi et al.

(1984)Smyth (1975) Lager & Meagher

(1978)Lager & Meagher(1978)

Lager & Meagher(1978)

Hazen and Finger(1987)

Olivine Thermal Expansion

End-member Forsterite Forsterite Fayalite Fayalite Monticellite ChrysoberylFormula Mg2SiO4 Mg2SiO4 Fe2SiO4 Fe1..94Mn0.11Mg0.04SiO4 Ca0.99Mg0.91Fe0.09SiO4 Al2BeO4 LiScSiO4

Sample Synthetic Synthetic Synthetic Natural Natural Natural syntheticPmax (GPa) 5.0 14.9 4.2 14.0 6.2 6.25 5.6KT0 (GPa) 132 123 113 132 113 242 118K’ 4.0 (fixed) 4.3 4 (fixed) 4 (fixed) 4 (fixed) 4 (fixed) 4 (fixed)Axial Compressions (10-3 GPa-1)a 1.6 1.5 0.8 1.2 1.96 1.09 2.70b 4.3 2.8 5.8 4.0 3.62 1.47 2.80c 0.8 2.7 1.4 1.3 2.05 1.32 2.61Site bulk moduli (GPa)M1 120 140 130 150 180 84M2 100 130 130 110 300 204Si >550 190 >500 >400 >300 300 315Reference Hazen (1976) Kudoh &

Takeuchi (1985)Hazen (1977) Kudoh & Takeda (1986) Sharp et al. (1987) Hazen (1987) Hazen et al.

(1996)

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 (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)

Cell Volume vs Fo#

290

290.5

291

291.5

292

292.5

90 92 94 96 98 100

Fo#

Un

it C

ell V

olu

me

(Å^3

) SC

CS SS0004

SS0003

SS0001

Fo100

M2 Vol vs Mg Occupancy

12.43

12.44

12.45

12.46

12.47

12.48

12.49

12.5

12.51

12.52

90 92 94 96 98 100

Fo #

M2

Vo

lum

e (

Å^

3)

SC

CS

SS0004SS0003

SS0001

Fo100