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Val Malenco, Central Alps, Italy: a source of gem materials (Abstract/Comunicazione in atti di convegno)
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- Val Malenco, Central Alps, Italy: a source of gem materials (Abstract/Comunicazione in atti di convegno) (literal)
- Anno
- 2014-01-01T00:00:00+01:00 (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
- 10.3301/ROL.2014.140 (literal)
- Alternative label
Adamo I.
Bocchio R.
Diella V. (2014)
Val Malenco, Central Alps, Italy: a source of gem materials
in 87° Congresso della Società Geologica Italiana e 90° Congresso della Società Italiana di Mineralogia e Petrologia, milano, 10-12 09 2014
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- Adamo I.
Bocchio R.
Diella V. (literal)
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- The Future of the Italian Geosciences - The Italian Geosciences of the Future (literal)
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- Istituto Gemmologico Italiano, Milano
Dipartimento di Scienze della Terra, Università degli Studi di Milano
CNR - Istituto per la Dinamica dei Processi Ambientali, Milano (literal)
- Titolo
- Val Malenco, Central Alps, Italy: a source of gem materials (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#curatoriVolume
- B. Cesare, E. Erba, B. Carmina, L. Fascio, F.M. Petti, A. Zuccari (literal)
- Abstract
- A distinguish feature of Val Malenco, Central Alps, Italy, is the remarkable number of recovered minerals (more
than 250 species), which have attracted the interest of mineralogists since the end of 18th century, making the valley
renowned at international level. Among the various minerals, some have a significant gemological interest and are used
in jewelry as gems or ornamental carvings.
The most notable and one of the best Italian gem material is the green andradite garnet (Ca3Fe2Si3O12), known with
the varietal name \"demantoid\" (Adamo et al., 2009). Attractive gemstones have been produced from crystal recovered
in asbestos mines hosted by serpentinites and located in a small area, where the most famous localities are: Cengiàsc
(including the Sferlùn quarry), Dossi di Franscia, Coston d'Acquanegra, Valbrutta, and Al Ross (Bedogné et al., 1993).
These asbestos deposits, now closed for safety reasons, are sited at ~1800-2200 m above sea level. The gemological
properties, including the characteristic \"horse-tail\" inclusions (fibrous chrysotile), and the chemical composition (Adr
>=98 mol%) are typical of serpentinites-related demantoid. Trace of chromium, together with major iron, are responsible
for the green color of this gem.
Another interesting gem material is the nephrite jade, discovered at Alpe Mastabia and hosted in a talc-tremolitic
orebody, associated with dolomitic marbles (Adamo & Bocchio, 2013). The jade, occurring as intergrowth of fine
fibers, is mainly composed of pure tremolite, Ca2Mg5Si8O22(OH)2, and contains a low concentration of iron, which
causes its typical pale green color. The occurrence of other constituents, including calcite, molybdenite and galena,
influences the color of the jade.
Gem-quality rhodonite (Mn5Si5O15) from Val Malenco occurs in the Mn-mineralization at Monte del Forno.
Rhodonite has typically a massive aspect, with an attractive pink color (due to Mn). It is always associated with
tephroite, spessartine, pyroxmangite, biotite, magnetite, calcite, quartz, and Mn-oxides and hydroxides.
\"Noble\" serpentine, green and yellowish green in color, composed mainly of lizardite and antigorite (with various
amount of calcite, dolomite, brucite, and chlorite) was found at Pizzo Tremogge included in forsterite-bearing marbles.
In the same area, precious Mn-rich clinozoisite (clinothulite variety) has also mined for its fine pink color.
Other interesting gem materials from Val Malenco include diopside (green or, more rarely, blue) and Cr-bearing
green grossular. (literal)
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