The Origin of Myrmekites in the Granitic Rocks of Ambagaspitiya, Sri Lanka

Myrmekite occurs in four distinct modes in the granitic rocks of Ambagaspitiya. Intragranular myrmekite (1) occurs completely within microcline grains, while marginal myrmekite (2) is confined to the rims of microcline grains and these two types of myrmekites are abundantly developed in the studied rocks. They invariably show corrosion features and the myrmekitic quartz may either protrude into or lie entirely in the adjacent microcline grain. Rim myrmekite (3) and intergranular myrmekite (4) occupy pJagioclase-microcline, and microcline-rnicrocline interfaces respectively. The four modes of occurrence of myrmekites described here are interpreted on the basis of exsolution and Becke's metasomatic exchange models in the light of the inferred geological history of the granitic rocks of Ambagaspitiya.

The study supports the view that myrmekite is polygenetic and different types of myrmekites in a suite of rocks may be formed by more than one unrelated process.