Not every rock is granite

Among the granites, the Archaeological Survey identifies two areas of Palaeozoic metasedimentary rocks. The Vila Nune area extends north-westwards along the Peio; the Gondiães area flanks the Beça. These references help explain the diversity underground; they are not visitor stops or collecting sites. The landscape gains another layer when we consider what it is made of.

To understand the name, separate two stages. Sediments can accumulate, become buried and consolidate into sedimentary rock. If that rock undergoes metamorphism, it changes under conditions such as high temperature and pressure. The term metasediment records this sedimentary origin followed by transformation.

Metamorphism does not mean melting: the USGS explains that transformation happens without the rock becoming magma. Minerals can reorganise or give way to others. In some rocks, elongated or flattened minerals become aligned and form a layered structure called foliation. Not every metamorphic rock has it.

These are tools for interpreting map terminology. They cannot assign a mineral, exact age or specific process to every stone in Vila Nune or Gondiães from its appearance alone. That requires connecting observation with mapping and geological study.