New model of agate geode formation

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Avatar utente
Marco E. Ciriotti
Messaggi: 25628
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy

New model of agate geode formation

Messaggio da Marco E. Ciriotti » ven 15 set, 2017 10:28

Prossima pubblicazione.

▪ Howard, C.B. & Rabinovitch, A. (2017): A new model of agate geode formation based on a combination of morphological features and silica sol–gel experiments. European Journal of Mineralogy, 29, (in press).

Agates are unable to be reproduced in a laboratory environment, and hence the mechanism of their formation remains unknown. Present hypotheses regarding genesis are thus, inevitably, speculative. We describe novel experiments, at room temperature and pressure, producing banded amorphous silica gel (via a sol–gel transition) whose morphology is compared to that of agates. In addition, macro- and microscopic examination of agates from several sites revealed some distinctive physical features: surface pitting, indentations of the agate bands, the variation in morphologies of the bands, thinning and narrowing of the bands around the indentations and the escape tubes, shapes of the coloured impurities and persistence of the sharp angle of the bands at sector boundaries. These observations and experimental data lead us to conclude that agates can be formed in four stages: sol–gel transition with concomitant band formation, formation of escape tubes, rapid crystallization from multiple nucleation sites and late dissolution/recrystallization of the inner layers.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»


Chi c’è in linea

Visitano il forum: Bing [Bot] e 6 ospiti