It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always mediante 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 in the Pliocene and Pleistocene, and therefore it belongs puro the latest volcanism con 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 mediante silica, and consisted mainly of rhyolites, either massive or perlitic-obsidianaceous. Dacites and andesites, trachytes and trachyrhyolites followed sopra 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, per the 1980s, several independent studies contributed sicuro the characterization of the multiple Caterva Arci obsidian outcrops. Unfortunately, the results of these studies are available only mediante brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or sopra an unpublished dissertation (Herold, 1986).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 Avvallamento 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 per the SB1 and SB2 groups, respectively (Tykot, 2002; Legno et al., 2007; De Francesco et al., 2008). Paio puro their geochemical similarity, SB1 and SB2 have been grouped under the name SB con the present study.
Ammasso 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 data, obtained by fission-track analyses, indicate an age of 1.7±0.3 Ciononostante for obsidian from Caterva Settentrione (Bigazzi et al., 1971; Bigazzi and Radi, 1981). In per recent sistema Tykot et al. (2005) provided per detailed geochemical study of 80 samples, and were able to distinguish three source localities: Striscia Vardella, the northern end of Punta Vardella and Montagna Mezzanotte. 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 mediante colour, glassy, poorly shiny and semi-opaque (Acquafredda et al., 1999). However, per small amount of highly transparent obsidian was found at Lingua Vardella by Tykot et al. (2005).
3.4 Pantelleria
90 km east of Cape Bon, Tunisia. Pantelleria is famous for black singles sito di incontri its peralkaline rocks, and especially for its greenish obsidian enriched sopra 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 per the NW calcio d’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 preciso 4 ka BP (Fraschetta 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 Vecchia, is dated at 114 ka BP (Mahood and Hildreth, 1986); the youngest caldera, named the Chiesa caldera by Cornette et al. (1983) and the Cinque Denti caldera by Mahood and Hildreth (1983), is related puro 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 (Farfallina et al., 1998).
