These aluminum anodes naturally wear away a little more like pumice

Aluminum rudder anode – wears away in larger pieces than zinc anodes

Aluminum shaft anode – wears away in larger pieces than zinc anodes

For comparison, these zinc anodes wear away a bit smoother than aluminum anodes

Zinc on the left, aluminum on the right. You can find any anode for your boat in aluminum (except pencil anodes for your engine)