It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always con synneusis with magnetite and olivine micro-phenocrysts (Acquafredda et al., 1999).

3.2. Sardinia: Mucchio Arci

30 km 2 and located in the hinterland of the gulf of Oristano. The volcanic activity developed during two distinct cycles durante the Pliocene and Pleistocene, and therefore it belongs to the latest volcanism con Sardinia. The magmatic products erupted during the second cycle, can be divided into four phases. The lavas erupted per the first phase were very rich sopra silica, and consisted mainly of rhyolites, either massive or perlitic-obsidianaceous. Dacites and andesites, trachytes and trachyrhyolites followed con chronological succession, until the last stages of volcanic activity, which were characterized by quiet eruptions of basaltic magma flows (Piras, 2002; Bigazzi et al., 2005).

The obsidian outcrops were described for the first time mediante the 19 th century by De La Marmora (1839–40). Subsequently, sopra the 1980s, several independent studies contributed preciso the characterization of the multiple Mucchio Arci obsidian outcrops. Unfortunately, the results of these studies are available only in brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or in an unpublished dissertation (Herold, 1986).

More recently, considering the geochemical features the obsidian of Caterva Arci, Tykot (2002) subdivided them into four groups, SA, SC, SB1 and SB2. The obsidian sampled near Conca Cannas and Uras are clustered within the SA group; those sampled near Pau, Perdas Urias and Sonnixeddu belong sicuro the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are in the SB1 and SB2 groups, respectively (Tykot, 2002; Nave et al., 2007; De Francesco et al., 2008). Coppia preciso their geochemical similarity, SB1 and SB2 have been grouped under the name SB durante the present study.

Montagna Arci obsidian populations are characterized by large biotite micro-phenocrysts (50–200 ?m), abundant crystals of feldspar (plagioclase and alkali feldspar) 50 ?m in size, orthopyroxene, magnetite, monazite and ilmenite (Acquafredda et al., 1999).

3.3. Palmarola

Geochronological data, obtained by fission-track analyses, indicate an age of 1.7±0.3 Ma for obsidian from Montagna Regioni nordiche (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Sopra verso recent sistema Tykot et al. (2005) provided a detailed geochemical study of 80 samples, and were able onesto distinguish three source localities: Striscia Vardella, the northern end of Striscia Vardella and Mucchio Nord. However, given the small size of the island, this distinction can be considered irrelevant from an archaeological point of view.

Palmarola obsidian contains micro-phenocrysts of clinopyroxene (5–20 ?m) and biotite. It is generally black per colour, glassy, poorly shiny and semi-opaque (Acquafredda et al., 1999). However, verso small amount of highly transparent obsidian was found at Striscia Vardella by Tykot et al. (2005).

3.4 Pantelleria

90 km east of Cape Bon, Tunisia. Pantelleria is famous for its peralkaline rocks, and especially for its greenish obsidian enriched con sodium and iron, known as Pantellerite (Farfallina et al., 1998; Acquafredda et al., 1999). Pantelleria has per bimodal distribution of magmatic products. Mafic lavas, exposed per the NW corner of the island, include transitional basalt and hawaiite (from

62 to 72 wt.% SiO₂), prevail in the SE sector (White et al., 2009). K–Ar determinations of mafic lavas done on different basaltic units give ages of 118 ± 9, 83 ± 5 and

29 ka BP (Farfallina et al., 1984). Ages determined on felsic volcanic rocks range from 324 ka BP puro 4 ka BP (Civetta et al., 1984, 1988, 1998; Mahood and Hildreth, 1986). The volcanic history of the island is characterized by large explosive eruptions, some of which produced caldera collapses, alternating with periods dominated by less energetic eruptions (Farfallina et al., 1998). The oldest caldera, named La Antenata, is dated at 114 ka BP (Mahood and Hildreth, 1986); the youngest caldera, named the Camposanto caldera by Cornette et al. (1983) and the Cinque Denti caldera by Mahood and Hildreth (1983), is related to the eruption of the Green Tuff (50 ka BP; Orsi and Sheridan, 1984). The more recent (post-50 ka) history of the island has been subdivided by Fraschetta et al. (1998) into six sialic eruptive cycles, intercalated with basaltic eruptions. The Green Tuff is considered the first of these six cycles. All the others are dated at around 35–29, 22, 20–15, 14–12 connexion sito di incontri and 10–4 ka BP, respectively (Civetta et al., 1998).