Distribuzione dello stilpnomelano nel Paleozoico del Brianzonese ligure

Antonio Cerro; Renato Gianotti; Mario Vanossi; Fernando Veniale

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti (1971)

  • Volume: 50, Issue: 3, page 345-355
  • ISSN: 0392-7881

Abstract

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Over two thousand thin sections of crystalline, igneous, volcanic and sedimentary epimetamorphic rocks from the paleozoic basement of the ligurian Briançonnais have been examined. About 2% of them contain needles, flakes, and sheaf-like aggregates; their pleochroism ranges from brown to yellowish in most cases (ferri-stilpnomelane, always associated with K-feldspar bearing rocks and often growing on K-feldspar crystals), or, more rarely, from green to yellow-greenish or colorless (ferro-stilpnomelane, in rocks without any obvious K-feldspar). The first one also forms on hornblende, biotite and chloritoid; the second one on sericite, chlorite and cryptocrystalline argillitic groundmass. The stilpnomelane is nearly always set within microfractures and cleavage fissures of the host minerals, or along their borders. The needles lie across foliation, thus indicating their post-tectonic crystallization. Special chemical conditions, such as availability of Fe and K and relatively low concentration of Mg and Al, together with locally favourable conditions of mobility, often connected with cataclastic texture of the rock, seem to be overall needed for the formation of stilpnomelane. However, its geographic distribution suggests that the zoneographic position of the rock at time of development of stilpnomelane might perhaps have facilitated or prevented its segregation.

How to cite

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Cerro, Antonio, et al. "Distribuzione dello stilpnomelano nel Paleozoico del Brianzonese ligure." Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti 50.3 (1971): 345-355. <http://eudml.org/doc/296137>.

@article{Cerro1971,
author = {Cerro, Antonio, Gianotti, Renato, Vanossi, Mario, Veniale, Fernando},
journal = {Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti},
language = {ita},
month = {3},
number = {3},
pages = {345-355},
publisher = {Accademia Nazionale dei Lincei},
title = {Distribuzione dello stilpnomelano nel Paleozoico del Brianzonese ligure},
url = {http://eudml.org/doc/296137},
volume = {50},
year = {1971},
}

TY - JOUR
AU - Cerro, Antonio
AU - Gianotti, Renato
AU - Vanossi, Mario
AU - Veniale, Fernando
TI - Distribuzione dello stilpnomelano nel Paleozoico del Brianzonese ligure
JO - Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti
DA - 1971/3//
PB - Accademia Nazionale dei Lincei
VL - 50
IS - 3
SP - 345
EP - 355
LA - ita
UR - http://eudml.org/doc/296137
ER -

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