Textural evolution of polyhedral olivine experiencing rapid cooling rates     

François Faure  Pierre Schiano  Gilles Trolliard  Christian Nicollet  Bernard Soulestin 《Contributions to Mineralogy and Petrology》2007,153(4):405-416

Dynamic crystallization experiments in the CaO–MgO–Al₂O₃–SiO₂ (CMAS) system have been used to investigate the change in crystal shape when pre-existing polyhedral olivine crystals are cooled rapidly (1,639–2,182°C/h). Polyhedral olivines are crystallized initially in a first step using a slow cooling rate (2°C/h), then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event. During this second episode small dendritic olivines also nucleate within the liquid phase. Observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence: polyhedral ⇒ hopper polyhedral ⇒ dendritic polyhedral. This evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by Sunagawa (Bull Minér 104:81–87, 1981, Morphology of crystals, Terra Scientific Publishing Company, 1987) is proposed.  相似文献   

Contrasted modes of amphibole development in coronitic metagabbros: a TEM investigation     

G. Trolliard  M. Boudeulle  J. M. Lardeaux  J. L. Potdevin 《Physics and Chemistry of Minerals》1988,16(2):130-139

A TEM investigation of amphibole development in granulitic metagabbros is presented. Three different sites of amphibole nucleation and growth are observed: (i) in the clinopyroxene-plagioclase interphase boundaries, corresponding to a reconstructive transformation involving intercrystalline diffusion; (ii) along pyroxene fractures, with competition between inter- and intracrystalline diffusion; (iii) within the pyroxene crystals, through a topotactic conversion, controlled by intracrystalline diffusion. These different reaction sites are studied in order to discuss some aspects of reaction mechanisms within undeformed metamorphic rocks, putting into balance intracrystalline versus intercrystalline processes. According to the possible paths (crystal lattice and its defects, fractures and mineral interfaces), contrasted amounts of reaction products, together with different amphibole compositions are evidenced. These results indicate that the diffusion rate of Al, Fe, Mg and OH is the rate controlling factor for amphibole-forming reaction.  相似文献   

A developmental model of olivine morphology as a function of the cooling rate and the degree of undercooling   总被引：3，自引：2，他引：1  

Faure  François  Trolliard  Gilles  Nicollet  Christian  Montel  Jean-Marc 《Contributions to Mineralogy and Petrology》2003,145(2):251-263

We performed dynamic crystallization experiments in the CMAS system at 1 atm to investigate the evolution of the morphology of forsterite crystals as a function of cooling rate and degree of undercooling. In sections parallel to the (010) plane, we observed the evolution of the forsterite morphology from tablets to hopper (skeletal) crystals, and then to swallowtail shapes (dendritic morphology) for increased degree of undercooling. The other shapes described in the literature can be interpreted as particular sections of those three shapes. The onset of dendritic growth is due to a competition between the growth of the faces of the initial hopper crystal and dendrite overgrowths. The forsterite dendrites are formed by a succession of units which look like hopper shapes. This result has been tested by an additional set of experiments.  相似文献