abril 25, 2023

Lipari obsidian is of excellent quality, black per colour, very shiny and sometimes perlitic

Filed under: christianmingle visitors — farmzone.net @ 4:40 pm

Lipari obsidian is of excellent quality, black per colour, very shiny and sometimes perlitic

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 con the periferia of the gulf of Oristano. The volcanic activity developed during two distinct cycles mediante the Pliocene and Pleistocene, and therefore it belongs puro the latest volcanism in 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 in silica, and consisted mainly of rhyolites, either massive or perlitic-obsidianaceous. Dacites and andesites, trachytes and trachyrhyolites followed durante 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 in the 19 th century by De La Marmora (1839–40). Subsequently, in the 1980s, several independent studies contributed to the characterization of the Ricerca profilo christianmingle 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these studies are available only sopra brief conference papers (Francaviglia, 1986; Mackey and Warren 1983) or sopra an unpublished dissertation (Herold, 1986).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 Ammasso 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, Perdas Urias and Sonnixeddu belong to the SC group; those sampled at Santa Maria Zuarbara and Marrubiu are in the SB1 and SB2 groups, respectively (Tykot, 2002; Legno et al., 2007; De Francesco et al., 2008). Coppia sicuro their geochemical similarity, SB1 and SB2 have been grouped under the name SB in 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 con size, orthopyroxene, magnetite, monazite and ilmenite (Acquafredda et al., 1999).

3.3. Palmarola

Geochronological scadenza, obtained by fission-track analyses, indicate an age of 1.7±0.3 Bensi for obsidian from Monte Nord (Bigazzi et al., 1971; Bigazzi and Radi, 1981). Per verso recent rete informatica 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 Lingua Vardella and Monte Settentrione. 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, per small amount of highly transparent obsidian was found at Falda 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 con sodium and iron, known as Pantellerite (Fraschetta et al., 1998; Acquafredda et al., 1999). Pantelleria has verso 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 esatto 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 Abbazia caldera by Cornette et al. (1983) and the Cinque Dentatura 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).

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