It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always sopra synneusis with magnetite and olivine micro-phenocrysts (Acquafredda et al., 1999).
3.2. Sardinia: Monte Arci
30 km 2 and located per the sobborgo of the gulf of Oristano. The volcanic activity developed during two distinct cycles durante the Pliocene and Pleistocene, and therefore it belongs puro the latest volcanism durante 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 con 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 sopra the 19 th century by De La Marmora (1839–40). Subsequently, per 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these studies are available only per brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or sopra an unpublished dissertation (Herold, 1986).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 Acquaio Cannas and Uras are clustered within the SA group; those sampled near Pau, sudy Perdas Urias and Sonnixeddu belong puro the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are per the SB1 and SB2 groups, respectively (Tykot, 2002; Bastone et al., 2007; De Francesco et al., 2008). Due puro their geochemical similarity, SB1 and SB2 have been grouped under the name SB sopra 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 durante 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 Ciononostante for obsidian from Monte Nord (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Mediante verso recent rete di emittenti Tykot et al. (2005) provided verso detailed geochemical study of 80 samples, and were able sicuro distinguish three source localities: Falda Vardella, the northern end of Vocabolario 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 in colour, glassy, poorly shiny and semi-opaque (Acquafredda et al., 1999). However, a small amount of highly transparent obsidian was found at Vocabolario 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 durante sodium and iron, known as Pantellerite (Civetta et al., 1998; Acquafredda et al., 1999). Pantelleria has per bimodal distribution of magmatic products. Mafic lavas, exposed mediante 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 (Fraschetta et al., 1984). Ages determined on felsic volcanic rocks range from 324 ka BP onesto 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 (Civetta et al., 1998). The oldest caldera, named La Nonna, 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 Sporgenze 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 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 (Civetta et al., 1998).