Myrmekites from the Haast Schists, New Zealand

Myrmekitic oligoclase grains in the garnet and oligoclase-zone schists of the Haast River differ from common myrmekites in two main ways: (1) they occur in rocks generally devoid of K-feldspar; (2) they are not grain-boundary features but form mosaics often constituting a major component of thick rock masses. The intergrowths are found in the quartzofeldspathic folia and are associated with ordinary poikiloblastic and non-poikiloblastic oligoclases of the same age. Textural gradations between myrmekite and ordinary poikiloblastic oligoclases indicate that the myrmekite represents inclusion of recrystallizing quartz in blastic oligoclase. This, and various other hypotheses of myrmekite formation, are briefly discussed.