It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always durante synneusis with magnetite and olivine micro-phenocrysts (Acquafredda et al., 1999).
3.2. Sardinia: Caterva Arci
30 km 2 and located durante the periferia 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 per Sardinia. The magmatic products erupted during the second cycle, can be divided into four phases. The lavas erupted con the first phase were very rich durante 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 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, con the 1980s, several independent studies contributed esatto the characterization of the multiple Ammasso Arci obsidian outcrops. Unfortunately, the results of these studies are available only con brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or per an unpublished dissertation (Herold, 1986).
More recently, considering the geochemical features the obsidian of Montagna Arci, Tykot (2002) subdivided them into four groups, SA, SC, SB1 and SB2. The obsidian sampled near Lavabo Cannas and Uras are clustered within the SA group; those sampled near Pau, Perdas Urias and Sonnixeddu belong esatto the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are con the SB1 and SB2 groups, respectively (Tykot, 2002; Nave et al., 2007; De Francesco et al., 2008). Paio to their geochemical similarity, SB1 and SB2 have been grouped under the name SB per 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 in size, orthopyroxene, magnetite, monazite and ilmenite (Acquafredda et al., 1999).
3.3. Palmarola
Geochronological tempo, obtained by fission-track analyses, indicate an age of 1.7±0.3 Pero for obsidian from Montagna Regioni nordiche (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Per a recent sistema Tykot et al. (2005) provided per detailed geochemical study of 80 samples, and were able esatto distinguish three source localities: Punta Vardella, the northern datingranking.net/it/fitness-singles-review end of Pezzo Vardella and Ammasso 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, per small amount of highly transparent obsidian was found at Punta 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 mediante sodium and iron, known as Pantellerite (Farfallina et al., 1998; Acquafredda et al., 1999). Pantelleria has a bimodal distribution of magmatic products. Mafic lavas, exposed con 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 (Civetta et al., 1984). Ages determined on felsic volcanic rocks range from 324 ka BP to 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 (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 Chiesa caldera by Cornette et al. (1983) and the Cinque Denti caldera by Mahood and Hildreth (1983), is related esatto 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).
