How 2 distinquish zinc vs magnesium anodes?

[johnb]

I purchased a boat, used in fresh water, and with "zinc" anodes all in good condition. How can I tell whether these anodes are actually zinc or magnesium? I'm putting the boat in salt water and want to make sure I've got the right metal. Is there an easy way to tell? Can I pull on and look at markings somewhere?

 

[Yachtsea]

I know if no easy way to tell. Magnesium is lighter. That may only help you if you had one of each in your hand.