Atomic Positional Parameters
Si1 2b 0.3333 0.6667 0.0748
Mg1 3c 0.3322 0.0000 0.4557
O1  2b 0.3333 0.6667 0.2920
O2  3c 0.5045 0.0000 -0.0082
O3  3c 0.6655 0.0000 0.5899

O4  1a 0.0000 0.0000 0.3080
H1  3c 0.5800 0.0000 0.7380
H2  1a 0.0000 0.0000 0.2000

Reference
M Mellini and PF Zanazzi (1987) Crystal structures of lizardite-1T and lizardite-2H1 from Coli, Italy. American Mineralogist, 72, 943-948.

Mineral Chemistry
Serpentine is formed by low-temperature hydration of the magnesium silicates olivine, pyroxene and amphibole, and describes a group of minerals with a composition approximating H₄Mg₃Si₂O₉. Serpentine crystal structures may be refined in trigonal, monoclinic, or orthorhombic space groups. The polymorphic forms of serpentine are chrysotile, a type of asbestos, antigorite and lizardite, each of which are based on a sheet of linked SiO₄ tetrahedra joined to a brucite layer such that two thirds of hydroxyl (OH) groups are replaced by silicon-bonded oxygens. The serpentine structure, which is built on tri-octahedral brucite, may be compared with kaolinite, which has di-octahedral gibbsite layers.

The dimensions of the brucite and SiO₄ sheets do not match exactly resulting in curved crystal structures. Chrysotile and antigorite both show crystallographic and structural evidence for curved structures, while lizardite is an extremely fine-grained and platy material. In fibrous chrysotile, the mismatch results in continuous bending into cylindrical tubes while in antigorite the misfit within layers forms a corrugated structure. In lizardite, variations in stacking of the layers lead to different "polytypes". The structure shown here is '1T' (trigonal); 2H1 is a double-layered hexagonal form. Lizardite is named after the Lizard in Cornwall, England.

The CHIME figure shows lizardite, with magnesium ions as green, oxygens as red, and silicons as ochre spheres. Hydrogens are white.