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Rondeau, B., Gauthier, J.-P., Mazzero, F., Fritsch, E., Bodeur, Y. & Chauvire, B. (2013) ON THE ORIGIN OF DIGIT PATTERNS IN GEM OPAL. Gems Gemol. 49 138–146.
Added by: Laurent Cournède (2016-03-10 21:23:30) |
| Type de référence: Article DOI: 10.5741/GEMS.49.3.138 Numéro d'identification (ISBN etc.): 0016-626X Clé BibTeX: Rondeau2013 Voir tous les détails bibliographiques  |
Catégories: MIOPS Mots-clés: ethiopia, of-color opal, precious opal Créateurs: Bodeur, Chauvire, Fritsch, Gauthier, Mazzero, Rondeau Collection: Gems Gemol. |
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| Résumé |
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Some natural opals, mostly from Ethiopia, show a macroscopic finger-like structure called a digit pattern. This pattern consists of vertical columns that are more or less parallel, separated by a homogeneous matrix of different color, transparency, or play-of-color. This study proposes that digits develop through: (1) the deposition of a homogeneous opal layer and subsequent polygonization in the form of vertical columns; (2) preferential alteration of this layer at the vertical grain and sub-grain boundaries, creating the digit shape; (3) precipitation of a new silica gel in the space between the digits; and (4) the drying and solidification of the opal. Although polygonization in the form of vertical columns is a growth process typical of synthetic opal, the post-growth alteration of these columns into digits and the deposition of matrix are observed only in natural opal.
Added by: Laurent Cournède |