Under BlueSchist facies conditions, the blue glaucophane-rich metabasites (metabasalts or metagabbros) are called BlueSchists or, where glaucophane is particularly abundant, glaucophanites. On the island of Groix, these rocks form boudins of variable size in the micaschistes :
The rocks of the "Lavoir" site on the island of Groix show a paragenesis typical of these glaucophanites. The dark blue millimetre levels are rich in Glaucophane (blue amphibole) and the yellow levels are rich in epidote. |
The colour contrast is sharp in sunlight. Notice in the middle of the picture, the small fuchsite crystal, a green chromium mica. At the top of the photo, an orange quartz level is also visible. |
Blue amphibole forms centimetric thick rods |
The rock may also have contained large centimetric prisms of lawsonite ... Microscopic observation shows a rhombus-shaped section of lawsonite now completely pseudomorphosed, (i.e. transformed into other minerals while retaining its original form) into paragonite (white sodic mica), epidote +/- chlorite.
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