How much is a 1965 copper quarter worth?
A quarter could appear to be copper in at least 3 different
ways. One's valuable, the other 2 aren't.
If the coin is the same weight and thickness as a normal
quarter, then it's either been exposed to something (heat,
chemicals) to change its color, or plated as part of a high-school
chemistry experiment. I can attest to the latter, having done the
same thing when we were learning about the electromotive series.
Both of these cases are considered to be altered coins so they have
no numismatic value.
However, if the coin is thinner than a normal quarter and the
images are weaker, you might have what's called a lamination error.
That error happens when the outer cladding doesn't bond to the
coin's copper core properly and falls off. Lamination errors can be
worth $10 or so.
Unless the coin is obviously thinner than a normal quarter,
you'd need to have it examined in person by someone experienced in