http://www.cnr.it/ontology/cnr/individuo/prodotto/ID209545
Gem-quality zoisite from Merelani (Northeastern Tanzania): review and new data (Articolo in rivista)
- Type
- Label
- Gem-quality zoisite from Merelani (Northeastern Tanzania): review and new data (Articolo in rivista) (literal)
- Anno
- 2012-01-01T00:00:00+01:00 (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
- 10.2451/2012PM0022 (literal)
- Alternative label
Rosangela Bocchio1,*, Ilaria Adamo1,Valentina Bordoni2, Franca Caucia2 and Valeria Diella3 (2012)
Gem-quality zoisite from Merelani (Northeastern Tanzania): review and new data
in Periodico di mineralogia (Testo stamp.)
(literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
- Rosangela Bocchio1,*, Ilaria Adamo1,Valentina Bordoni2, Franca Caucia2 and Valeria Diella3 (literal)
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- Note
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- 1Dipartimento di Scienze della Terra \"A. Desio\" Università degli Studi di Milano
2Dipartimento di Scienze della Terra e dell'Ambiente, Università degli Studi di Pavia
3Consiglio Nazionale delle ricerche (C.N.R.), Istituto per la Dinamica dei Processi Ambientali (IDPA),
Sezione di Milano (literal)
- Titolo
- Gem-quality zoisite from Merelani (Northeastern Tanzania): review and new data (literal)
- Abstract
- The Merelani area (NE Tanzania) is the unique locality in the world for tanzanite, a violetish
blue gem-quality variety of vanadium-rich zoisite. However, other coloured (brown, yellow,
orange, etc.) zoisite occurs in this deposit, closely associated with tanzanite. This study reports
a review and new data on physical and chemical properties of this material, obtained
investigating five gem-quality samples, ranging in colour from yellowish brown and greenish
yellow to violetish blue, by means of classical gemmological methods and by XRD, EMP
and LA-ICP-MS analyses. The results confirm that the major element concentration of all the
samples is almost identical, so their different colour is mainly dependent on the variation of
some minor and trace elements. In particular, the main chromophore element is V but also
the V/Ti ratio plays a significant role in the colour characteristics. All the faceted gems have
been subjected to heat treatment in order to observe a possible change of their colour. The
various coloured zoisite gems become permanently blue and change their pleochroic scheme
from trichroic to dichroic at ~ 500 °C, except for the blue specimen which is dichroic before
and after heating and does not show any change of colour. The oddness of this sample could
be due to an undeclared previous heat treatment, made to enhance the colour. All these
characteristics observed in zoisite from Merelani derive from the geological history that makes
it one of the most interesting and significant gem deposit of the world. (literal)
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