Abstract
The revelation of fossil charged-particle tracks due to very heavy cosmic ray nuclei ( Z > 22) in meteoritic minerals and due to spontaneous fission fragments ( 238 U and 252 Cf) in terrestrial minerals was experimentally studied. Sodium hydroxide was found to be the ideal etchant for the entire group of plagioclase feldspars and several pyroxene species. Controlled etching at 120°–160°C reveals “proper” tracks in these minerals. The tracks formed are nearly cylindrical with sharph defined tips allowing reproducible and accurate track length measurements. A useful outcome of these experiments was the observation that controlled etching can fairly unambiguously help ascertain the position of a mineral species of a single given crystal in the solid solution series under consideration: the dispersion in etching-times for normal development of known terrestrial or meteoritic mineral species is small enough (in most cases) to distinguish neighbouring species. As an aid to easy and complete optical viewing of etch-tracks, we injected a concentrated blue dye solution into the track holes. This considerably increases the optical contrast. Colouring of etch tracks allows reliable measurements of track lengths and easy counting of track densities in the neighbourhood of 10 3 –10 4 /cm 2 , as often encountered for terrestrial minerals.
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