GRANODIORITE
This geological formation constitutes much of western Elba, forming the Mount Capanne massif, whose peak towers over the neighbouring elevations, rising 1019 metres above the sea. It is an intrusive igneous rock, whose colour ranges from light grey to darker grey, belonging to the granite family and believed to have formed six to seven million years ago. Its essential mineral components are plagioclase, orthoclase, quartz and biotite, with accessory ones including apatite, zircon, magnetite, tourmaline, allanite, rutile and uraninite. It has a granular texture and a solid structure with a medium to fine grain.

Granodiorites have a similar composition to that of type S granites, deriving from fusions of crustal rocks and, indeed, one is easily confused with the other, particularly to the untrained eye. Both these rocks, in any case, belong to the larger family of granitoid rocks. To enter into further detail, geologists now maintain that the mass constituting the majority of Mount Capanne is monzogranite or, more specifically, leucomonzogranite, due to its particularly pale colour, breaking it down into three bodies of rock (or 'facies') differing slightly in chemical composition and texture (geometry of the various mineral components). These three masses are known as the San Piero facies, the San Francesco facies (most extensive by exposed surface area) and the Sant'Andrea facies, in the area of the Via dei Lentischi.

Elba's granodiorite often features visible orthoclase crystals, sometimes spectacular and twinned, with dark inclusions essentially composed of minute plagioclase and biotite crystals, probably portions of mantle captured within igneous rock of more superficial origin. This is particularly true in the coastal area of Sant'Andrea (due to the aforementioned Sant'Andrea facies), especially in the section between Capo Sant'Andrea and the Cotoncello beach, where eye-catching white crystal alternating with striking dark bodies stand out from the pale grey granodiorite mass.