Central-western Elba is home to porphyry, an intrusive and subvolcanic igneous rock produced by generally acidic magma. the term derives from the Greek word porfyroús, meaning purple, which is frequently the colour of this type of rock. Its structure is distinguished by large, visible crystalline elements such as quartz and feldspar, embedded in a usually reddish groundmass.
Those found on this island are generally granite or granodiorite porphyry. The more recent porphyries are embedded in Mount Capanne ('orano porphyry'), while the older and perhaps better-known specimens are those intruded into the cap rock overlying the pluton that rose and then slid to the east. These can be divided into two groups: older 'Portoferraio porphyry' (8 million years old), comprising masses and veins found between Enfola and the base of the Portoferraio peninsula, crossing the island and reaching Lacona bay, and 'San Martino porphyry' (7.3 million years old), whose masses extend a little further west, from the Punta Penisola, La Biodola and Procchio areas to above Marina di Campo bay (the ones we encounter on this walk).
These igneous rocks are mainly composed of crystals, often clearly visible, of quartz, plagioclase, potassium feldspar and biotite, and have a yellowish colour in varying degrees of brightness. This yellow stone can be seen, for instance, in the sea gate in Portoferraio, and is the stone used in combination with pink limestone to create the historic centre of this town, the island's capital. Porphyry was, indeed, used in decorative elements and to pave the old roadway, and the warm hue of this stone goes perfectly with the pinkish shade of limestone, mirroring the colours in which the buildings may have been painted, also featuring the warm colours of pink or yellow ochres.
Breakdown of porphyry over the millennia due to constant erosion by the elements, transforming it into pale and golden sand, has contributed to creating some of the island's most beautiful beaches, like those of La Biodola and Procchio and, to a degree, also those of Marina di Campo and Lacona.
