Lizardite

Crystal System: Hexagonal,Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Magnesium silicate hydroxide
Chemical Formula: Mg3Si2O5(OH)4
Method(s) of Verification: Anglesey – XRD (Maltman, 1977); Rhiw – XRD (Natural History Museum, no. 5920F).

Chemical Group:

  • Silicates

Geological Context:

  • Hydrothermal: serpentinization
Dark green lizardite from Rhoscolyn, Holy Island, Anglesey. Specimen 8 cm across. National Museum of Wales Collection (NMW 83.15G.M.1). Photo T.F. Cotterell, © National Museum of Wales.
Introduction: lizardite belongs to the kaolinite-serpentinite group of minerals and is one of three minerals (antigorite, lizardite and chrysotile) commonly referred to as ‘serpentine’. Antigorite and lizardite are soft green platy minerals, whereas chrysotile is fibrous. These minerals commonly result from the hydrothermal or retrograde metamorphism of mafic minerals such as olivine, pyroxene or amphibole, in ultrabasic rocks. Lizardite is the most common of the three serpentine minerals and is typically found with brucite and magnetite.
Occurrence in Wales: lizardite has been recorded from two occurrences of ultrabasic rocks in Wales.

Key Localities:

  • Holy Island, Anglesey: lizardite occurs associated with antigorite in serpentinized peridotite bodies within the New Harbour Group (Monian Supergroup) metasediments. Textures show that the lizardite replaces primary olivine and orthopyroxene (Maltman, 1977).
  • Rhiw, Llŷn, Gwynedd: the presence of lizardite, in ultrabasic rocks of the Rhiw Intrusion, has been confirmed by X-ray diffraction analysis.

There are no key localities for this specimen.

References:

  1. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
  2. Maltman, A.J., 1977. Serpentinites and related rocks of Anglesey. Geological Journal, 12, 113-128.

There are no references for this specimen.