Serpentine
Group
Presentation prepared by Oliver Boyd
Serpentine: A Phyllosilicate
Formula: Mg3Si2O5(OH)4
End Members: Lizardite,
Chrysotile, and
Antigorite
Serpentine: A Phyllosilicate
Serpentine: Structure
Member
Lizardite
Chrysotile
Antigorite
Crystal System
Triclinic
T – P31m
H1 – P63cm
Monoclinic
A2/m
Monoclinic
Pm or P2/m
a
5.308
5.313
43.53
b
9.2
9.12
9.26
c
42.712
14.637
7.26

90.0
90.0
90.0

90.0
93.167
91.6

90.0
90.0
90.0
Z
12
4
16
Volume (Å3)
2085.78
708.15
2926.12
Density (kg/m3)
2658
2609
2526
Serpentine: Structure
Serpentine: Occurrence
Serpentine minerals commonly occur as alterations
of magnesium silicates, especially olivine, pyroxene,
and amphibole. The following is a possible reaction:
Mg2SiO4 + 3H2O Mg3Si2O5(OH)4 + Mg(OH)2
Associated with magnesite, chromite, and magnetite,
it is found in both igneous and metamorphic rocks and
may make up the entire rock mass. Chrysotile is the
asbestiform variety of serpentine. It is extensively
mined and is the primary asbestos mineral.
Serpentine: Occurrence
Fig. 4 from Angel et al. 2001. The
maximum thermal stability of hydrous
phases in sediment (Ono, 1998), MORB
basalt (Schmidt and Poli, 1999), and
ultramafic harzburgite (Frost, 1999) bulk
compositions. Positions of the –-, –and -Pv + MW transformations for
(Mg1.8Fe0.2)SiO4 are shown in gray (Ito and
Takahashi, 1989; Katsura and Ito, 1989). An
average mantle adiabat (ama), an estimate
of the minimum temperature in a
subducting slab (cs), and the antigorite
breakdown curve (ant) are also shown
(Jeanloz and Morris, 1986; Ulmer and
Trommsdorff, 1995; Irifune et al., 1996;
Stein and Stein, 1996).