Micro-structural phenomena in agate/chalcedony: spiral growth

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Rispondi
Avatar utente
Marco E. Ciriotti
Messaggi: 24906
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Micro-structural phenomena in agate/chalcedony: spiral growth

Messaggio da Marco E. Ciriotti » mer 03 ott, 2018 11:34

Prossima pubblicazione.

Referenza:
▪ Götze, J., Berek, H., Schäfer, K. (2018): Micro-structural phenomena in agate/chalcedony: spiral growth. Mineralogical Magazine, 82, (in press).

Abstract:
Agates with spectacular micro-structural features were found in volcanic rocks of several occurrences in the Saar-Nahe region (Germany). These agates include spirals of several tens up to several hundreds of μm in size within zones lacking the characteristic structural agate banding. A combined mineralogical study by polarizing microscopy, scanning electron microscopy (SEM), cathodoluminescence (CL) microscopy and spectroscopy as well as electron backscatter diffraction (EBSD) provided evidence that the spirals consist of well-ordered trigonal α-quartz, whereas the surrounding matrix is composed of strongly disordered 18 or amorphous SiO2 phases. The quartz micro-crystals show a systematic rotation of the crystal orientation perpendicular to the direction of the spiral loops indicating helical growth.
It is assumed that the spiral growth is initiated by dislocations with a screw component. The lacking symmetry of the strongly disordered or amorphous matrix initiated a curved development by a screw dislocation in a system far from equilibrium. The atoms/molecules are packed into spiral layers, which is energetically favoured in comparison with the incorporation into plane crystal faces. Such kind of self-organization growth and polymerization initiated by a screw dislocation can produce variable spiral morphologies sometimes resembling living forms.
Marco E. Ciriotti

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

Rispondi

Chi c’è in linea

Visitano il forum: Google [Bot] e 2 ospiti