Date of Award


Document Type


Degree Name

Bachelor of Science (BS)



First Advisor

Dr. Frank R. Karner


Textural relationships indicate that the structure of aegirine augite controlled the secondary formation of hornblende in the Tunk Lake granite. In the marginal rocks of the granite body some grains of aegirine augite may be partially or completely enclosed by hornblende. Hornblende also replaces aegirine augite along fractures. Extensive replacement results in grains which have small cores of aegirine augite surrounded by hornblende. Cleavage patterns and optical orientations of the two minerals indicate that their c axes are parallel. Pyroxene can be transformed to hornblende by a minor shift in orientation of its basic tetrahedral structure. Chemical changes necessary in the transformation are the addition of water, a slight decrease in sodium and the substitution of some aluminum for silicon. The transformation of aegirine augite to hornblende was caused by an increase in magma water vapor pressure and a decrease in temperature.