Plane polarised light
The glaucophane schist is from the forestry track at the west end of Llyn Llwydiarth SH546787, Anglesey, Wales. cf. Map.Given by Brian Young.

Glaucophane belongs to the alkali amphibole group of minerals. It is easily distinguished from other amphiboles by its striking blue colour. It is the essential amphibole in blueschists which form under high pressure low temperature conditions in metamorphosed rocks at destructive plate margins and are commonly found in ophiolite suites. In this case the original rock was a silt/mudstone.
The quartz vein running through the section is 0.2mm thick.


Crossed polarised lightOften associated with glaucophane schists is epidote. It can be distinguished by its higher birefringence (giving brighter colours under crossed polars) as seen in the above picture towards the bottom left (blue-red) and top right (green).
Epidote in plane polarised light is colourless to to a pale yellowish green as can be seen in the left hand picture.
Both photo's show a quartz vein.

Map: Created with Memory-Map. ©Crown Copyright. Licence number 100034184.

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