# The Alteration of Giglio Island Granite: Relevance to the Conservation of Monumental Architecture
## 1 Introduction  
Granitic rocks are natural stones that have always fascinated humans, who associated them with characteristics of hardness and great resistance to atmospheric agents. Their use, however, especially because of their hardness, requires special techniques, both for extraction and processing, and has always been linked to technological evolution [1; 2]. The examples, even grandiose, of the use of granite rocks for both structural and decorative elements are widespread all over the world. However, these stones, like all others, are in any case subjected to the decay phenomena that develop in a more striking and rapid manner depending on the textural characteristics and exposure to particular climates that induce transformation phenomena of feldspathic minerals, leading to the complete disintegration of the rock [3; 4; 5; 6; 7; 8]. In Italy, the use of granite rocks in monuments and historical architecture is not widespread because there are few outcrops except for the north-eastern part of Sardinia, where these rocks crop out extensively and are still quarried alongside their use as building material in civil architecture [9; 10]. For the rest, most of the granite rocks come from the western and central Alps and were used in the 1800s and early 1900s for decorative and architectural elements. Among these, we can mention the granite of Baveno, Montorfano, San Fedelino, Alzo, Quarona, the Traversella diorie, the Balma sienite, and the Adamello tonalite [1; 11; 12]. However, in the Imperial Age, the Romans made extensive use of granite rocks in the Italian territory, making them arrive above all from the numerous quarries opened in the eastern Egyptian desert and Asia Minor, using them as columns in monumental architecture. In this search for granite rocks, the Romans also sourced to a lesser extent in Sardinia and in two islands of the Tuscan archipelago, Elba and Giglio [1]. As for Giglio island, the granite was quarried particularly from the 3 rd century on the east coast of the island. These quarries directly overlook the sea, and this has placed Giglio in a \"privileged\" condition compared to Elba for the extraction of this rock. The oldest quarry probably was opened at the time of [PERSON] and was exploited at least until the early 19 th century. It is the _Cava del Foriano_, also called _\"alle colomte\"_ by the islanders, situated above the village of Giglio Porto, with traces of the extraction still visible. Other quarries can be seen near Punta Arenella (_Piccione_ and _Arenella_ quarries), Punta del Lazzaretto, Scalettino di Giglio Porto, Cala delle Cannelle (_Gran Cava_), and also at Cala delle Caldane (_Bonsere_). The quarries were cultivated intermittently until the middle of the last century (Figure 1). These quarries were famous above all for the export of beautiful columns, big monoliths weighing several tons, due directly into the sea front of the quarries, which were then transported by rollers and pontoons on ships. Examples are the six granite columns in the Roman Villa of Domizi Enobarbi in Giannutri island, in the Neronian Port of Anzio, in Rome in the porch of S. Lorenzo in Lucina (first two columns from the right), in the Romanesque porch of via Santi Quattro Coronati, in the pronaos of Santa Croce di Gerusalememme, in the Cancelleria Palace (two columns in the upper and lower colonnade, respectively), in Santa Maria Maggiore (two columns in the left side of the porch), in Sant'Anastasia (four columns, the first and last of the central nave), in Pieve di Santa Maria Assunta di San Leo, in the Forum of Caesar, in Naples in the Church of Gerolomini (12 columns) [12], and in the facade of the Royal Palace (eight columns) from shafts lying in the Foriano quarry. Columns of Giglio origin, probably from the bare of Roman monuments, are present in the Pisa Bell tower (Figure 2), in San Piero a Grado Basilica near Pisa, in the Florence Baptistery, and in the Cathedral of Gaeta.