Ilsestein granite lies on the northern perimeter of the Harz and is part of the Brocken massif. It occurs in a vein-like deposit, 11 kilometres long and 2 kilometres wide. The magma of the Ilsestein granite was probably the last magma intrusion in the Brocken complex. It is the most quartz-rich granite in the Brocken complex. Its quartz and orthoclase elements grew together. Its utility and hardness as a construction stone is reduced by the numerous geodes, up to 5 cm across.