Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Magnesium silicate hydroxide
Chemical Formula: Mg3Si2O5(OH)4
Method(s) of Verification: Mynachdy, Anglesey - visual (Greenly, 1919); Cefn Coed Colliery - XRD as 'amesite or chrysotile' (Natural History Museum, X-ray no. x2724).

Chemical Group:

  • Silicates

Geological Context:

  • Hydrothermal: serpentinization
Introduction: chrysotile 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.
Occurrence in Wales: chrysotile has been recorded from just two occurrences in Wales, one from ultrabasic rocks from Anglesey and the other from the Coal Measures strata in South Wales.

Key Localities:

  • Cefn Coed Colliery, Neath: a mineral from the Dulais Seam at Cefn Coed Colliery has been identified as 'amesite or chrysotile'. This is an unusual environment for chrysotile to form in and therefore requires further investigation.
  • Mynachdy, N. Anglesey: Greenly (1919) described the occurrence of chrysotile in a small quarry formerly worked for asbestos at this locality. The quarry exploited a small intrusion of serpentinized ultrabasic rock, ophicalcite and altered dolerite.


  1. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).