Mix tapioca flour and sugar together, and blend mixture into the berries.
Line a pie dish with pastry. Pour filling into pie shell, and cover with top crust. Seal edges by pinching or fluting the edge. Brush top with egg white and sprinkle with a little sugar. Cut slits in top to allow steam to escape.
Bake at 350 degrees F (175 degrees C) for 30 to 40 minutes, until pie is golden brown and bubbly.