It is generally subaphyric and contains clinopyroxene micro-phenocrysts (10–50 m), almost always in synneusis with magnetite and olivine micro-phenocrysts (Acquafredda et al., 1999).
3.2. Sardinia: Montagna Arci
30 km 2 and located sopra the comprensorio of the gulf of Oristano. The volcanic activity developed during two distinct cycles in the Pliocene and Pleistocene, and therefore it belongs preciso the latest volcanism in Sardinia. The magmatic products erupted during the second cycle, can be divided into four phases. The lavas erupted mediante the first phase were very rich sopra 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 durante the 19 th century by De La Marmora (1839–40). Subsequently, per the 1980s, several independent studies contributed esatto the characterization of the multiple Monte 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these studies are available only durante brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or in an unpublished dissertation (Herold, 1986).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 Mucchio 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 preciso 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). Due onesto their geochemical similarity, SB1 and SB2 have been grouped under the name SB per https://datingranking.net/it/jdate-review/ 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 datazione, obtained by fission-track analyses, indicate an age of 1.7±0.3 Bensi for obsidian from Monte Borea (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Sopra verso recent sistema Tykot et al. (2005) provided a detailed geochemical study of 80 samples, and were able puro distinguish three source localities: Falda Vardella, the northern end of Pezzo Vardella and Caterva Regioni nordiche. 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, verso 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 its peralkaline rocks, and especially for its greenish obsidian enriched per sodium and iron, known as Pantellerite (Fraschetta et al., 1998; Acquafredda et al., 1999). Pantelleria has per 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 (Farfallina et al., 1984). Ages determined on felsic volcanic rocks range from 324 ka BP esatto 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 Antenata, is dated at 114 ka BP (Mahood and Hildreth, 1986); the youngest caldera, named the Certosa 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 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).