Transcript Olivine Group

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
b
a
g
Olivine Thermal Expansion
End-Member
Formula
Sample
T range
Unit cell
aV (x 10-5 K-1)
aa (x 10-5 K-1)
ab (x 10-5 K-1)
ac (x 10-5 K-1)
Polyhedral Volumes
M1
M2
T
NPV
Reference
Forsterite
Mg2SiO4
Synthetic
23-1600ºC
Fayalite
Fe2SiO4
Synthetic
20-900ºC
Liebenbergite
Ni2SiO4
Synthetic
25-900ºC
Monticellite
CaMg0.93Fe0.07SiO4
Natural
25-795ºC
Glaucochroite
Ca0.98Mn0.87Mg0.10SiO4
Natural
25-800ºC
Chrysoberyl
Al2BeO4
Natural
25-690ºC
4.36
1.12
1.67
1.46
(x 10-5 K-1)
4.32
5.07
0
4.40
Takeuchi et al.
(1984)
3.19
0.99
0.95
1.19
3.44
1.19
1.11
1.12
2.97
1.01
0.99
1.13
3.17
1.05
1.00
1.09
2.39
0.74
0.85
0.83
2.88
4.51
-1.17
3.37
Smyth (1975)
4.19
3.68
0.36
3.33
Lager & Meagher
(1978)
4.68
3.62
-1.23
3.20
Lager & Meagher
(1978)
4.55
4.01
-2.13
2.81
Lager & Meagher
(1978)
2.25
3.89
2.57
1.99
Hazen and Finger
(1987)
Olivine Compression
End-member
Formula
Sample
Pmax (GPa)
KT0 (GPa)
K’
Axial Compressions
ba
bb
bc
Site bulk moduli (GPa)
M1
M2
Si
Reference
Forsterite
Mg2SiO4
Synthetic
5.0
132
4.0 (fixed)
(10-3 GPa-1)
1.6
4.3
0.8
Forsterite
Mg2SiO4
Synthetic
14.9
123
4.3
Fayalite
Fe2SiO4
Synthetic
4.2
113
4 (fixed)
Fayalite
Fe1..94Mn0.11Mg0.04SiO4
Natural
14.0
132
4 (fixed)
Monticellite
Ca0.99Mg0.91Fe0.09SiO4
Natural
6.2
113
4 (fixed)
Chrysoberyl
Al2BeO4
Natural
6.25
242
4 (fixed)
LiScSiO4
synthetic
5.6
118
4 (fixed)
1.5
2.8
2.7
0.8
5.8
1.4
1.2
4.0
1.3
1.96
3.62
2.05
1.09
1.47
1.32
2.70
2.80
2.61
120
100
>550
Hazen (1976)
140
130
190
Kudoh &
Takeuchi (1985)
>500
Hazen (1977)
130
130
>400
Kudoh & Takeda (1986)
150
110
>300
Sharp et al. (1987)
180
300
300
Hazen (1987)
84
204
315
Hazen et al.
(1996)
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#
Unit Cell Volume (Å^3)
292.5
SC
292
CS
291.5
SS0004
SS0003
291
SS0001
290.5
Fo100
290
90
92
94
96
Fo#
98
100
M2 Vol vs Mg Occupancy
12.52
SC
M2 Volume (Å^3)
12.51
12.5
CS
12.49
SS0004
12.48
SS0003
12.47
12.46
SS0001
12.45
12.44
Fo100
12.43
90
92
94
96
Fo #
98
100