R5 - Epidosite

Fine-grained rock with a double coloration, due to the pale green patches rich in epidote and pale white patches rich in quartz. The sample comes from the “Coquand Section”, a Tuscan geosite where a sequence of white marble to sulfide bearing skarn is exposed, crosscut by magmatic intrusions (mafic and acid) and epidotised acidic porphyry bodies (Da Mommio et al., 2010; http://www.alexstrekeisen.it/meta/epidosite.php). Epidosite is a rock mainly made of epidote and quartz and forms by hydrothermal metamorphism on a parent igneous rock (protolith). The protolith can be: basic, like for the epidotized basic bodies, deep in oceanic spreading ridges (https://www.sandatlas.org/epidosite/); acid, as for the epidosite in the “Coquand Section” that formed where the acidic magmatic intrusions cut the skarn deposit (Geol.F.Trips, Vol.7 No.1.2 (2015), DOI 10.3301/GFT.2015.02).

Thin section description: 

The PPL view shows green coloured crystals of epidote (Ep) often enclosed in larger colourless quartz (Qz) grains (poikiloblastic). In the XPL view, the Ep crystals exhibit the characteristic high birefringence, with very bright and variable interference colours, while the Qz crystals show low birefringence value with white to grey interference colours.

Thin section PPL	Thin section XPL