Andradite variety demantoid from Val Malenco, Sondrio, Italy
Demantoid is the yellowish green to green variety of andradite, a species belonging to the garnet group, with ideal chemical composition Ca3Fe2(SiO4)3. Because its rarity and incomparable brilliance, resembling that of diamond, demantoid is the most highly prized of all garnets. Among the most notab...
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Società Italiana di Mineralogia
2009
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ftunivmilanoair:oai:air.unimi.it:2434/67525 2024-01-28T10:09:38+01:00 Andradite variety demantoid from Val Malenco, Sondrio, Italy I. Adamo R. Bocchio A. Pavese V. Diella P. Vignola V. Palanza I. Adamo R. Bocchio V. Diella A. Pavese P. Vignola V. Palanza 2009 http://hdl.handle.net/2434/67525 eng eng Società Italiana di Mineralogia Forum italiano di scienze della terra : Geoitalia volume:35 firstpage:734 lastpage:735 journal:PLINIUS http://hdl.handle.net/2434/67525 andradite variety demantoid EMP and LA-ICP-MS measurements REE distribution UV-Vis-IR spectroscopy Settore GEO/06 - Mineralogia info:eu-repo/semantics/article 2009 ftunivmilanoair 2024-01-02T23:20:55Z Demantoid is the yellowish green to green variety of andradite, a species belonging to the garnet group, with ideal chemical composition Ca3Fe2(SiO4)3. Because its rarity and incomparable brilliance, resembling that of diamond, demantoid is the most highly prized of all garnets. Among the most notable localities for andradite variety demantoid, there is Val Malenco, in the province of Sondrio, Lombardy, northern Italy, where the mineral is found in well-shaped crystals contained into asbestos-filled lithoclases crosscutting the outcrops of the serpentinites formation (Amthauer et al., 1974; Bedogné et al., 1993). This study aims to provide an overview of andradite variety demantoid from Val Malenco, Italy, investigating a suite of gem-quality samples from this locality, including both faceted gemstones and roughs, by means of EMP and LA-ICP-MS chemical analyses, X-ray powder diffraction, and UV-Vis-NIR and mid-IR spectroscopic measurements. For comparison, we studied also demantoids from other significant localities, including Ural Mountains (Russia), Erongo Mountains (Namibia), Kerman Province (Iran), Pakistan, and Val d’ Aosta (Italy). The investigated samples from Val Malenco have a wide range of colors, varying from yellowish or brownish green to green. The faceted gems are all singly refractive with moderate to strong anomalous double refraction, with refractive indices >1.79 and density from 3.79 to 3.88 g/cm3. The space group Ia3d with unit cell parameters a=b=c= 12.0623(1)-12.0629(1) Å, and V= 1755.05(4)-1755.33(4) Å3 are typical of andradite garnet (Deer et al., 1997), as well as the mid-IR pattern (Moore et al., 1971). The spectrum also shows absorption features related to hydroxide, incorporated as minor component, in the form of structurally bonded OH- groups (Amthauer and Rossman, 1998). In a sample we also found dark nuclei of chromium-bearing magnetite which spread their Cr contents into the garnet. Chemical analyses show that all samples from different localities are almost pure andradites ... Article in Journal/Newspaper ural mountains The University of Milan: Archivio Istituzionale della Ricerca (AIR) Rossman ENVELOPE(-82.800,-82.800,-79.783,-79.783) |
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collection |
The University of Milan: Archivio Istituzionale della Ricerca (AIR) |
op_collection_id |
ftunivmilanoair |
language |
English |
topic |
andradite variety demantoid EMP and LA-ICP-MS measurements REE distribution UV-Vis-IR spectroscopy Settore GEO/06 - Mineralogia |
spellingShingle |
andradite variety demantoid EMP and LA-ICP-MS measurements REE distribution UV-Vis-IR spectroscopy Settore GEO/06 - Mineralogia I. Adamo R. Bocchio A. Pavese V. Diella P. Vignola V. Palanza Andradite variety demantoid from Val Malenco, Sondrio, Italy |
topic_facet |
andradite variety demantoid EMP and LA-ICP-MS measurements REE distribution UV-Vis-IR spectroscopy Settore GEO/06 - Mineralogia |
description |
Demantoid is the yellowish green to green variety of andradite, a species belonging to the garnet group, with ideal chemical composition Ca3Fe2(SiO4)3. Because its rarity and incomparable brilliance, resembling that of diamond, demantoid is the most highly prized of all garnets. Among the most notable localities for andradite variety demantoid, there is Val Malenco, in the province of Sondrio, Lombardy, northern Italy, where the mineral is found in well-shaped crystals contained into asbestos-filled lithoclases crosscutting the outcrops of the serpentinites formation (Amthauer et al., 1974; Bedogné et al., 1993). This study aims to provide an overview of andradite variety demantoid from Val Malenco, Italy, investigating a suite of gem-quality samples from this locality, including both faceted gemstones and roughs, by means of EMP and LA-ICP-MS chemical analyses, X-ray powder diffraction, and UV-Vis-NIR and mid-IR spectroscopic measurements. For comparison, we studied also demantoids from other significant localities, including Ural Mountains (Russia), Erongo Mountains (Namibia), Kerman Province (Iran), Pakistan, and Val d’ Aosta (Italy). The investigated samples from Val Malenco have a wide range of colors, varying from yellowish or brownish green to green. The faceted gems are all singly refractive with moderate to strong anomalous double refraction, with refractive indices >1.79 and density from 3.79 to 3.88 g/cm3. The space group Ia3d with unit cell parameters a=b=c= 12.0623(1)-12.0629(1) Å, and V= 1755.05(4)-1755.33(4) Å3 are typical of andradite garnet (Deer et al., 1997), as well as the mid-IR pattern (Moore et al., 1971). The spectrum also shows absorption features related to hydroxide, incorporated as minor component, in the form of structurally bonded OH- groups (Amthauer and Rossman, 1998). In a sample we also found dark nuclei of chromium-bearing magnetite which spread their Cr contents into the garnet. Chemical analyses show that all samples from different localities are almost pure andradites ... |
author2 |
I. Adamo R. Bocchio V. Diella A. Pavese P. Vignola V. Palanza |
format |
Article in Journal/Newspaper |
author |
I. Adamo R. Bocchio A. Pavese V. Diella P. Vignola V. Palanza |
author_facet |
I. Adamo R. Bocchio A. Pavese V. Diella P. Vignola V. Palanza |
author_sort |
I. Adamo |
title |
Andradite variety demantoid from Val Malenco, Sondrio, Italy |
title_short |
Andradite variety demantoid from Val Malenco, Sondrio, Italy |
title_full |
Andradite variety demantoid from Val Malenco, Sondrio, Italy |
title_fullStr |
Andradite variety demantoid from Val Malenco, Sondrio, Italy |
title_full_unstemmed |
Andradite variety demantoid from Val Malenco, Sondrio, Italy |
title_sort |
andradite variety demantoid from val malenco, sondrio, italy |
publisher |
Società Italiana di Mineralogia |
publishDate |
2009 |
url |
http://hdl.handle.net/2434/67525 |
long_lat |
ENVELOPE(-82.800,-82.800,-79.783,-79.783) |
geographic |
Rossman |
geographic_facet |
Rossman |
genre |
ural mountains |
genre_facet |
ural mountains |
op_relation |
Forum italiano di scienze della terra : Geoitalia volume:35 firstpage:734 lastpage:735 journal:PLINIUS http://hdl.handle.net/2434/67525 |
_version_ |
1789339749858672640 |