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Giglio Island, Grosseto Province, Tuscany, Italy

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Location is approximate, based on center of defined region.
Latitude & Longitude (WGS84): 42° North , 10° East (est.)
Name(s) in local language(s):Isola del Giglio, Provincia di Grosseto, Toscana, Italia

The Island of Giglio (23.8 km2), one of the seven islands that constitute the Tuscan Archipelago, is separated by a 16-kilometre stretch of sea from the nearest point of the mainland, the promontory of Monte Argentario. Mainly mountainous, it culminates in the Poggio della Pagana (496 m a.s.l.). The island belongs to a municipality of the province of Grosseto, whose official name is Isola del Giglio, composed of the islands of Giglio and Giannutri.

The larger part of Giglio Island consists of Pliocene monzogranite intrusions. Metamorphic and sedimentary rocks of Jurassic to Triassic age form the small Franco Promontory on the western side (Lazzarotto et al., 1964).

The island is a unique site to study the link between the syn- and the post-orogenic processes that affected the internal portions of the northern Apennine orogenic wedge in the Tyrrhenian region. Ferrocarpholite-bearing rocks representing the exhumed deep root of the orogenic wedge are in fact in tectonic contact with Pliocene intrusives, which in turn are products of thermal relaxation processes that accompanied the late extensional attenuation of the previously thickened orogenic crust (Rossetti et al., 1999).

The Giglio Monzogranite Intrusion (GMI) comprises two different monzogranitic intrusions of an overall S-type peraluminous and sub-alkaline composition, with an average Rb/Sr radiometric cooling age of 5.0 Ma (Westerman et al., 1993). The main intrusive body is characterised by an outer zone that is strongly foliated and locally layered (Pietrabona Facies) and an inner zone that is porphyritic and homogeneously textured (Arenella Facies). All the GMI rocks consists of the same primary mineral assemblage, namely dominant K-feldspar, albitic plagioclase, quartz, and biotite with minor muscovite, tourmaline, apatite, and zircon. The presence of strongly pinitised cordierite is ubiquitous; garnet, andalusite, monazite, rutile, and titanite occur sporadically (Faggioni et al., 1998).
A small leucocratic pluton, the Scole monzogranite intrusion, also intruded the GMI along the mid-point of the eastern shore of the island (Westerman et al., 1993). It crops out at Le Scole, a group of rocks located less than 100 meters from shore (Le Scole have gained notoriety in recent times because one of these rocks caused the shipwreck of the Costa Concordia cruise liner).

At the Franco Promontory, similar to the nearby Monte Argentario [see: http://www.mindat.org/loc-12330.html], the stacking of three different tectonostratigraphic units has been observed. The rock assemblage mainly consisting of ferrocarpholite-bearing metasediments (predominately quartz-rich phyllites and schists belonging to the Tuscan Verrucano sequence) crops out extensively along the western part of the promontory and constitutes the lowermost unit of the whole nappe complex. The other two units are made of metaophiolitic rocks and Calcare Cavernoso (grey limestones, dolostones, and breccias).

Note: the island derives its name from the goats, in fact it was called "Aigylion (Αιγύλιον) mikros" by the Ancient Greeks (while Capraia Island was "Aigylion megas"). The Greek name was later transformed into Aegilium or Igilium by the Romans and Gilio during the Middle Ages.

Mineral List

Mineral list contains entries from the region specified including sub-localities

56 valid minerals.

Localities in this Region

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- Brocchi G.B. (1818): Osservazioni naturali fatte nel promontorio Argentario e isola del Giglio. Bibl. Ital.- Giorn. Lett. Sc. Arti, 11, 76-93, 237-253, 356-369.
- Pareto L. (1844): Sulla costituzione geologica delle isole di Pianosa, Giglio, Giannutri, Montecristo, e Formiche di Grosseto. In: Atti della quarta unione degli scienziati italiani tenuta in Lucca nel settembre 1843. Sezione di geologia, mineralogia, e geografia. Atti del dì 27 Settembre 1841. Tip. Giusti, Lucca, pages 269-272.
- Jervis G. (1874): I tesori sotterranei dell'Italia. Vol. 2: Regione dell’Appennino e vulcani attivi e spenti dipendentivi. Ed. Loescher, Torino, 624 pp.
- Jervis G. (1881): I tesori sotterranei dell'Italia. Vol. 3: Regioni delle Isole. Sardegna e Sicilia. Addenda ai precedenti volumi. Loescher, Torino, XXII+539 pp.
- Lotti B. (1883): Appunti di osservazioni geologiche nel promontorio Argentario, nell’isola del Giglio e nell’isola di Gorgona. Boll. R. Comitato Geol. d'Italia, 4, 5-6, 109-128.
- Lazzarotto A., Mazzanti R., Mazzoncini F. (1964): Geologia del Promontorio Argentario (Grosseto) e del Promontorio del Franco (Isola del Giglio - Grosseto). Boll. Soc. Geol. Ital., 83, 2, 1-124.
- Del Caldo A., Moro C., Gramaccioli C.M., Boscardin M. (1973): Guida ai minerali. Fratelli Fabbri Editori, Milano, 208 pp.
- De Michele V. (1974): Guida mineralogica d'Italia. Istituto Geografico De Agostini, Novara, 2 vol., 408 pp.
- Barrese E., Della Ventura G., Di Sabatino B., Ciriaco G., Di Lisa A. (1987): The thermometamorphic contact aureola around the Isola del Giglio granodiorite (Tuscany, Italy): petrography and petrogenetical considerations. Geologica Rom., 26, 349-357.
- Westerman D.S., Innocenti F., Tonarini S., Ferrara G. (1993): The Pliocene Intrusions of the Island of Giglio. Mem. Soc. Geol. It., 49, 345-363.
- Marinai V., Nannoni R. (1994): I minerali dell’Isola del Giglio. Circolo Culturale Gigliese, Pacini Editore, Pisa, 48 pp.
- Faggioni O., Westerman D., Innocenti F., Beverini N., Carmisciano C., Cavallini R., Dini A. (1998): The intrusive complex of the Island of Giglio: geomagnetic characteristics of plutonic facies with low susceptibility contrast. Annali di Geofisica, 41, 3, 409-425.
- Jolivet L., Faccenna C., Goffè B., Mattei M., Rossetti F., Brunet Ch., Storti F., Funiciello R., Cadet J.P., D’Agostino N., Parra T. (1998): Mid-crustal shear zones in post-orogenic extension: example from the Northern Tyrrhenian sea. J. Geoph. Res., 103, B6, 123-160.
- Rossetti F., Faccenna C., Jolivet L., Funiciello R., Tecce F., Brunet C. (1999): Syn- versus postorogenic extension: the case study of Giglio Island (northern Tyrrhenian Sea, Italy). Tectonophysics, 304, 71-93.
- Reinhardt J., Rossetti F. (2004): Monte Argentario and Isola del Giglio (Southern Tuscany, Italy): a record from continental break-up to subduction, orogenic wedge formation, and post-orogenic extension. 32nd International Geological Congress (IGC), Florence, August 20-28, 2004. Post-Congress P61. Field Trip Guide Book - P61, 19 pp.
- Barsotti G., Nannoni R. (2006): Rocce, minerali e miniere delle isole dell'Arcipelago Toscano. Pacini Editore, Pisa, 152 pp.

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