Orbicules occur in a rock outcropping in granite-gneiss terrain near the village of Kamankese, Gold Coast. They are round to oblong, two to five centimeters wide, and consist of cores of pargasite and epidote with rims of plagioclase. The matrix is chiefly pargasite, epidote, and plagioclase. The orbicular structure is considered to result from the action of alkaline fluids permeating an inclusion of crushed amphibolite, with the feldspar rims growing around fragments in a way similar to the formation of concretions.

You do not currently have access to this article.