Photo-Emission Electron Microscopy (PEEM) Heating Investigations of a Natural Amphibole Sample

J.-A. Wartho*
Department of Earth Sciences, University of Leeds, Leeds, LS2 9JT, UK
*Present address: Department of Earth Sciences, Open University, Walton Hall, Milton Keynes, MK7 6AA. UK

Abstract: PEEM allows ‘real-time’ observations to be made of solid-state transformations and other high-temperature processes taking place during vacuum-heating up to c. 2000°C The solid state transformations of an amphibole-rich hornblendite specimen have been observed in the temperature range of 750–1000°C (± 50°C Between c. 970–990°C a rapid change in orientation contrast was observed, indicating a structural rearrangement from an oxyhornblende crystal lattice to a clinopyroxene structure. This phase retains the original amphibole shape and texture (including two 120°C intersecting cleavage traces), but possesses a clinopyroxene crystal structure. At higher temperatures this phase is seen to decompose, forming iron oxides and other fine-grained products. PEEM has provided useful information on both the nature and rates of transformation of natural amphiboles which has proved invaluable in our understanding of the mineralogically-controlled mechanisms of argon release during 40Ar/39Ar dating of amphibole samples.

Keywords: Photo-emission electron microscopy • vacuum-heating • amphiboles • solid state transformations

Mineralogical Magazine; March 1995 v. 59; no. 394; p. 121-127; DOI: 10.1180/minmag.1995.59.394.12
© 1995, The Mineralogical Society
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