I just remembered I have an collectors coin, went up stairs to get is, bought it 8 years ago on an official coin website, and it says online it's made of silver.
Metaal : Zilver
Gehalte : 925/1000
Gewicht : 15,50 g
Diameter : 33,0 mm
Randschrift : * GOD * ZIJ * MET * ONS
Kwaliteit : Proof
It's a 5 euro coin made in 2009 for the 400 year trade relation with Japan.
Very cool. You should look it up on e-bay. That will give you an idea of what its currently worth. Sometimes those specialty proof coins can fetch some nice dollars.
I looked it up on the Dutch eBay called marktplaats some people are selling it for 6 euros, it's weight is 15,5 grams but its not .999 pure. I think it's .925.
Ah, Sterling . Sounds like a nice coin. I'd keep it.