Towards the north of the area we are in, we can enter the Bohonal de Ibor berrocal (rocky area). These are coarse-grained granites, with megacrystals of quartz, orthoclase feldspar and micas. The whole is intensely fractured, showing the typical geomorphology of granitic berrocales, with an abundance of rounded blocks, boulders and ridges (e.g. Peraleda de San Román berrocal), whose rocks have been formed by an ascent of molten magma (magmatic intrusion) and subsequent cooling inside the earth’s crust. This intrusion was carried out by breaking up and assimilating into the magmatic mass the pre-existing rocks, in this case Palaeozoic slate, which, due to the effect of the magmatic heat, have undergone a series of transformations in their texture and mineralogical composition. It is a phenomenon known as contact metamorphism, or thermal metamorphism, since high temperatures predominate. The transformations are produced by recrystallisation, with a new regrouping and orientation of the minerals of the slates which, generating new minerals, give rise to different metamorphic rocks depending on the degree of pressure and temperature received, which will be more intense the closer we get to the contact with the magmatic intrusion. This zone is called the “contact aureole” or “metamorphic aureole”.
Slate, micaceous schist and mica schist can be found along the slopes of the road. On the surface, these rocks show alterations and a micaceous lustre due to the high content of micas (muscovite and biotite) which constitute them. They also show a typical slaty cleavage or schistosity (division into flags or thin rocks, with breaks in favour of multiple parallel planes), defined by the laminar orientation of the micas, acquired by the tectonic stresses generated by the emplacement of the granitic pluton between the Palaeozoic slates.
On these slopes, we also observe different vein-like intrusions in the form of dykes (a flat, narrow and elongated form of magmatic intrusion) embedded in fractures of Paleozoic-age slate, sandstone and quartzite. Some are of the aplitic type with small crystals and very clear, almost white colours; others, however, are of the pegmatitic type, in which large grains of quartz, micas and orthoclase feldspar have crystallised.
