The Red Rocks: 500-million-year-old porphyry
The massive porphyry outcrops rising from the sea at Arbatax are no mere picturesque boulders: they are volcanic formations dating back to the Palaeozoic era, roughly 500 million years old, among the oldest exposed rocks in Sardinia. Their ferrous colour — which shifts from orange to violet depending on the light — is due to the high concentration of oxidised potassium feldspar. In some places the layering reveals folds and fractures that geologists read as the scars of ancient continental orogenies. Photographed by millions of tourists, the Red Rocks have been chosen as a film set for more than one Italian production and lent their name to the island's most important music festival.