Crystal System: Monoclinic
Status of Occurrence: Unconfirmed Occurrence
Chemical Composition: Calcium aluminium silicate hydroxide
Chemical Formula: CaAl2(Al2Si2)O10(OH)2
Method(s) of Verification: None.
- Metamorphic: low-grade
- Metamorphic: medium-grade
Introduction: margerite belongs to the mica group of minerals. It is typically found in low- to medium-grade metamorphic rocks such as chlorite-schists, mica schists, and blueschists (glaucophane-bearing rocks) and in emery deposits. It is associated with aluminium-rich minerals such as corundum, diaspore, andalusite or other aluminium silicates (e.g. tourmaline, staurolite, glaucophane, chlorite), magnetite and spinel.
Occurrence in Wales: a tentative reporting of margarite from Wales was made by Greenly (1919), who suggested that high Ca contents in certain quartzites, might possibly be accounted for by the presence of margarite. No evidence was provided to support the identification of this mineral and subsequent petrological work (e.g. Phillips, 1989) has failed to make a positive identification.
There are no key localities for this specimen.
- Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).
- Phillips, E., 1989. The Geology of the Monian Supergroup, Western Anglesey, North Wales. Unpublished Ph.D. thesis, University of Wales.