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: Caterva 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 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 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 lava 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 puro the characterization of the multiple Mucchio Arci obsidian outcrops. Unfortunately, the results of these studies are available only sopra brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or sopra an unpublished dissertation (Herold, 1986).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 Monte 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 puro the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are mediante the SB1 and SB2 groups, respectively (Tykot, 2002; Legno et al., 2007; De Francesco et al., 2008). Coppia puro their geochemical similarity, SB1 and SB2 have been grouped under the name SB durante 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 durante 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 Mucchio Nord (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Durante a recent sistema Tykot et al. (2005) provided a detailed geochemical study of 80 samples, and were able to distinguish three https://datingranking.net/it/dominicancupid-review/ source localities: Lingua Vardella, the northern end of Striscia Vardella and Monte 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 sopra 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 its peralkaline rocks, and especially for its greenish obsidian enriched in sodium and iron, known as Pantellerite (Civetta et al., 1998; Acquafredda et al., 1999). Pantelleria has a bimodal distribution of magmatic products. Mafic lavas, exposed con the NW corner 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 (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 (Farfallina 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 Denti 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 (Civetta et al., 1998).