Orbicular Rocks from Closepet Granite Near Hoskote, Tumkur Dt., Karnataka

The paper records the first occurrence of Orbicular rocks from the Closepet Granitoid belt near Hoskote, Tumkur district, Karnataka. The orbicules occur in a dioritic country rock enclosed within grey Closepet Granitoid. These are multishelled orbicules with shells of plagioclase and hornblende with a core of the same minerals. There are also proto-orbicules. The chemical analyses of orbicules fall in mafic tonalite field on K₂O - CaO plots. Individual shells reflect a basic rock parentage. The orbicules are derived from a metabasic enclave due to granitic action by melting, diffusion and concretionary process in hydrous stage.