It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always per synneusis with magnetite and olivine micro-phenocrysts (Acquafredda et al., 1999).
3.2. Sardinia: Mucchio Arci
30 km 2 and located per the fascia periferica of the gulf of Oristano. The volcanic activity developed during two distinct cycles per the Pliocene and Pleistocene, and therefore it belongs puro the latest volcanism mediante Sardinia. The magmatic products erupted during the second cycle, can be divided into four phases. The lavas erupted sopra the first phase were very rich con silica, and consisted mainly of rhyolites, either massive or perlitic-obsidianaceous. Dacites and andesites, trachytes and trachyrhyolites followed mediante 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 sopra the 19 th century by De La Marmora (1839–40). Subsequently, mediante the 1980s, several independent studies contributed to the characterization of the multiple Ammasso Arci obsidian outcrops. Unfortunately, the results of these studies are available only durante brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or in an unpublished dissertation (Herold, 1986).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 puro the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are con the SB1 and SB2 groups, respectively (Tykot, 2002; Bastone et al., 2007; De Francesco et al., 2008). Paio preciso their geochemical similarity, SB1 and SB2 have been grouped under the name SB con the present study.
Caterva Arci obsidian populations are characterized by large biotite micro-phenocrysts (50–200 ?m), abundant crystals of feldspar (plagioclase and alkali feldspar) 50 ?m con size, orthopyroxene, magnetite, monazite and ilmenite (Acquafredda et al., 1999).
3.3. Palmarola
Geochronological datazione, obtained by fission-track analyses, indicate an age of 1.7±0.3 Ma for obsidian from Caterva Nord (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Mediante per recent rete di emittenti Tykot et al. (2005) provided per detailed geochemical study of 80 samples, and were able sicuro distinguish three source localities: Punta Vardella, the northern end of Pezzo Vardella and Ammasso Tramontana. 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 in colour, glassy, poorly shiny and semi-opaque (Acquafredda et al., 1999). However, per small amount of highly transparent obsidian was found at Pezzo 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 in sodium and iron, known as Pantellerite (Civetta et al., 1998; Acquafredda et al., 1999). Pantelleria has a bimodal distribution of magmatic products. Mafic lavas, exposed in the NW spigolo 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 sicuro 4 ka BP (Farfallina 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 Anziana, is dated at 114 ka BP (Mahood and Hildreth, 1986); the youngest caldera, named the Monastero caldera by Cornette et al. (1983) and the Cinque Dentatura caldera by Mahood and Hildreth (1983), is related sicuro 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 Farfallina 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 and 10–4 ka BP, respectively (Farfallina et al., 1998).