No quarters we're ever minted in 40% percent silver only half dollars from 1965 to 1970. Edit: @Goldsayshi463 if you are still going through quarter rolls I'd highly suggest checking each coin individually since the odds of finding silver are quite low.
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Usually, the edges will always have a copper line showing on each of the coins. If it has a dark color, black, or whatnot, it may or may not be silver because it could be something else on the edge causing the copper stripe to not appear as opposed to the dark patina caused by silver. In any case, I'd check the face of the coins anyway, because silver isn't the only thing I'd check for... Checking the edges of coins is simply the first thing I did out of habit.
I know this is an old thread but actually the Frisco bicentennial quarters for both business and proof strikes were 40% silver and 60% copper.