This is certainly one of the geosites of the Arouca Geopark where it is possible to observe better the macroscopic characteristics that allow us to distinguish schist rocks from granitoid rocks, once they are presented side by side, as the result of the severe lithological contact of NW-SE approximate direction and with an inclination of about 90 degrees.
The granite is presented under the shape of a residual relief, which stands out from the landscape, like it happens a little through the entire Freita mountain’s plateau. This rock, called Freita mountain’s granite, is a syn-tectonic magmatic, leuco to mesocratic rock, with a phaneritic of medium grain texture. Although it is described as a two mica granite, curiously, there is in this place a clear domain of the muscovite in relation to the biotite.
On the other side, the rocks formerly called “schists” correspond, in fact, to metasedimentary rocks, composed by an alternation of mica schists and metagraywackes, affected by the mid-level regional metamorphism, where it is possible to observe a schistosity of NW-SE to WSW-ESSE subvertical direction. In the biotite mica schist, staurolite and andalusite porphyroblasts stand out, also presenting some sillimanite (fibrolite), the latter possible to be observed only on a microscope, but whose presence indicates that the rocks are in the sillimanite area of the regional metamorphism.
Location: Arouca
The granite is presented under the shape of a residual relief, which stands out from the landscape, like it happens a little through the entire Freita mountain’s plateau. This rock, called Freita mountain’s granite, is a syn-tectonic magmatic, leuco to mesocratic rock, with a phaneritic of medium grain texture. Although it is described as a two mica granite, curiously, there is in this place a clear domain of the muscovite in relation to the biotite.
On the other side, the rocks formerly called “schists” correspond, in fact, to metasedimentary rocks, composed by an alternation of mica schists and metagraywackes, affected by the mid-level regional metamorphism, where it is possible to observe a schistosity of NW-SE to WSW-ESSE subvertical direction. In the biotite mica schist, staurolite and andalusite porphyroblasts stand out, also presenting some sillimanite (fibrolite), the latter possible to be observed only on a microscope, but whose presence indicates that the rocks are in the sillimanite area of the regional metamorphism.
Location: Arouca
