Acta naturalia Islandica - 01.07.1964, Page 7

ABSTRACT
The occurrence of an ultrabasic rock of Quaternary age is described, frorn
Hvammsmúli, Eyjafjöll, S.-Iceland. A study of structures and field relations
indicates that the roclcs represent a case of multiple intrusion, the main masses
being sills. Phenocrysts of olivine and clinopyroxene, which usually carry a mantle
of lower temperature composition, constitute about a third of tlie rock. Some of
the olivines described show iron exsolution of unusual intensity. Two types of
textures, granular and subophitic, were recognized. The main minerals tuere
studied optically and found to be of similar composition throughout the rocks.
The various rocks are therefore thouglit tp be closely related in time.