I think if you use the search you will find threads on this already. If I remember correctly you can tell by the spokes, I think there is a grove in the the spoke on the Aluminum ones which I dont see in your 2 in the photos.I have 2 Marchesini front wheels (3.5x17"), and can´t determine if they´re mag. or alu ones.
How much would they weigh and what would be the weightdifference between them?
Anyone has a clue?