Publication Date

2013

Document Type

Honors Thesis

Department

Geosciences

Keywords

Garnet, Nucleation-Experiments, Chlorite minerals, Cordierite, Pressure vessels, Experiment, Nucleation, Piston cylinder press, Chlorite, Gedrite

Abstract

Nucleation describes the process of when a mineral first begins to form on the microscopic level and the atoms align into the particular orientations of its crystal lattice. The volume of the crystal nucleus must also reach a critical size so that the decrease in Gibbs free energy from phase change is greater than the increase in Gibbs free energy due to surface energy of a small crystal. Minerals begin to grow because of chemical reactions that occur during metamorphism of a metamorphic rock or during the cooling of an igneous rock. For nucleation to occur, specific conditions must be in place. All of the elements necessary to create a mineral can be present in a rock, but unless the conditions are productive for nucleation, the mineral will not form. In the experiments described in this paper, I sought to discover specific experimental conditions that would promote nucleation of garnet. Chlorite, quartz, biotite, muscovite, and garnet were ground into powders and subjected to temperatures ranging from 610˚C to 750˚C and 8kbar pressure in a piston cylinder press for lengths of time ranging from 4 to 18 days. Water was added to half of the samples in order to determine if it would promote garnet nucleation. Products were analyzed on a Scanning Electron Microscope (SEM). Garnet nucleation only occurred for the longest experiment at the highest temperature (750˚C, 8kbar, 17 days and 20 hours). This temperature is 160˚C higher than the calculated minimum temperature for garnet nucleation and growth from chlorite + quartz at 8kbar. Perhaps if the lower temperature experiments were run for longer periods of time, garnet would have nucleated. Cordierite nucleation, gedrite nucleation, garnet overgrowth, and grain coarsening occurred in several of the experiments.

Language

English

Comments

vi, 85 p. : ill. (some col.) Honor projects-Smith College, 2013. Includes bibliographical references (p. 69-70)

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