Abstract: The morphology and structures of intergrowth precipitates in some Norwegian aventurinized plagioclases have been described in previous publications; data collected during an investigation of a wide variety of heat treatments upon the same specimens are now reported. In detail the behaviour of different feldspar crystals is highly individualistic, though there is a common pattern in sub-solidus reaction(s) with the feldspar; even if the identification of the products is uncertain, it is this process which causes the apparent ‘homogenization’ of the feldspar.

Some comparisons can be made between the present studies and the more limited experiments of earlier workers, and suggestions for reconciling experimental data are discussed. On the paragenesis of aventurinized feldspars, these heating experiments confirm that mechanism(s) are complex, but that exsolution from an originally iron-enriched feldspar by cooling in the solid state is unlikely to be of more than peripheral importance.