50% silver - great find! 
I sometimes found US quarters when searching bags of British 5p coins for silver in the 1980s (when shillings were still current as 5p) but I never found a silver quarter! Back then you might get one silver pre-1947 shilling for every 1,000 you searched.

I sometimes found US quarters when searching bags of British 5p coins for silver in the 1980s (when shillings were still current as 5p) but I never found a silver quarter! Back then you might get one silver pre-1947 shilling for every 1,000 you searched.