PPL: A eulysite is a
metamorphic rock consisting of Fe and Mn bearing silicates such as
the pyroxenes hedenbergite and hypersthene, the olivine fayalite and
the garnets almandine and spessartine. The greenish brown minerals
seen above are the pyroxenes, the garnets and olivines are pale
yellow brown and distinguishable under crossed polars in so far as
the former are isotropic under crossed polars. The opaques are magnetite.
(NB: The hand specimen does not conform to the thin section photo's).
The bright areas are magnetite (Fe3O4); when the hand specimen was
held over a compass, the needle was considerably deflected. Red-brown
colours, seen mainly towards the right are garnets. The rock is
deemed to be of Precambrian (Lewisian) age.
It was not until the 1930's that this type of
ultrabasic metamorphic rock was recognised in Britain. Previous
examples were mainly from Scandinavia.
On the map below, 411 refers to locality of above
specimen: 399 is locality of the pyroxenite.