Crystal System: Trigonal
Status of Occurrence: Confirmed Occurrence
Distribution: Locally Abundant
Chemical Composition: Magnesium hydroxide
Chemical Formula: Mg(OH)2
Method(s) of Verification: Holy Island - polarizing-light microscopy (Greenly, 1919).
Introduction: brucite is a white mineral when pure but may be greenish or brown when it contains impurities such as iron (as Fe2+) or manganese. It typically forms by the alteration of periclase (MgO) found metamorphosed dolomites and magnesian limestones metamorphosed at high tempertaures. It is also found as a low-temperature hydrothermal mineral in magnesium-rich rocks such as sepentinites or chlorite schists.
Occurrence in Wales: the only recording of brucite in Wales is by Greenly (1919) who described its presence in talc schist exposed on Holy Island, Anglesey.

Key Localities:

  • Holy Island, Anglesey: Greenly (1919) recorded bright green scales in talc schist derived from the alteration (serpentinization) of ultrabasic rocks exposed on the small islet in Rhyd-y-Bont Creek. No further data on this occurrence is currently available.


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