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: Monte Arci
30 km 2 and located per the hinterland of the gulf of Oristano. The volcanic activity developed during two distinct cycles durante the Pliocene and Pleistocene, and therefore it belongs sicuro the latest volcanism in Sardinia. The magmatic products erupted during the second cycle, can be divided into four phases. The lavas erupted durante the first phase were very rich in silica, and consisted mainly of rhyolites, either massive or perlitic-obsidianaceous. Dacites and andesites, trachytes and trachyrhyolites followed in chronological succession, until the last stages of volcanic activity, which were characterized by quiet eruptions of basaltic lava flows (Piras, 2002; Bigazzi et al., 2005).
The obsidian outcrops were described for the first time per the 19 th century by De La Marmora (1839–40). Subsequently, in the 1980s, several independent studies contributed sicuro the characterization of the multiple Montagna Arci obsidian outcrops. Unfortunately, the results of these studies are available only per brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or in an unpublished dissertation (Herold, 1986).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 Ammasso Arci, Tykot (2002) subdivided them into four groups, SA, SC, SB1 and SB2. The obsidian sampled near Lavandino 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 mediante the SB1 and SB2 groups, respectively (Tykot, 2002; Bastone et al., 2007; De Francesco et al., 2008). Paio to their geochemical similarity, SB1 and SB2 have been grouped under the name SB con the present study.
Monte Arci obsidian populations are characterized by large biotite micro-phenocrysts (50–200 ?m), abundant crystals of feldspar (plagioclase and alkali feldspar) 50 ?m per 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 Bensi for obsidian from Caterva Settentrione (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Con a recent work Tykot et al. (2005) provided verso detailed geochemical study of 80 samples, and were able onesto distinguish three source localities: Falda Vardella, the northern end of Pezzo Vardella and Montagna 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 con colour, glassy, poorly shiny and semi-opaque (Acquafredda et al., 1999). However, per small amount of highly transparent obsidian was found at Striscia Vardella by Tykot et al. (2005).
3.4 Pantelleria
90 km Ricerca spicymatch east of Cape Bon, Tunisia. Pantelleria is famous for its peralkaline rocks, and especially for its greenish obsidian enriched mediante sodium and iron, known as Pantellerite (Civetta et al., 1998; Acquafredda et al., 1999). Pantelleria has verso bimodal distribution of magmatic products. Mafic lavas, exposed durante the NW angolo 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 (Civetta 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 (Fraschetta 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 preciso 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 and 10–4 ka BP, respectively (Fraschetta et al., 1998).