AMYGDULES, DEFORMED

  The vesicles in eruptive rocks are usually filled in by minerals such as calcite, quartz or zeolite. These initial spherical amygdales are deformed to acquire ellipsoidal shapes after deformation with recrystallization or plastic deformation of the mineral species comprising the amygdales. The amygdales afford a good material for use in determining the finite strain in rocks. The photograph is of deformed amygdales in the Bhimtal area of Garhwal Himalaya (by Prof D K Shrivastava, IIT, Roorkee, India) at bottom while the one at top left is from the book by J G Ramsay 1967. The one at right by author was taken in 1996 from the "Mehroni schsit" supracrustal amphibolite in Central Indian Bundelkhand batholith.