Wow!
Not to get you all excited or anything but what you have may be a "foreign planchet" What you need to do is first look up the weight of a 1969 quarter, I will try to helps you with this by searching the net. Once you have the correct weight of the coin just simply weight that one to see if there is a vast difference in weight. I have no idea how it happens but there are US coins struck on foreign plachets quite abit. They can bring in some pretty good prices depending on what it is. Now if your quarter is determined to be a differant metal than the standard you will want to look up a man by the name of Fred Weinberg. He is out of California and is one of the most respected error experts in the world. I have spoken with him on about 3 occasions for his knowlage by phone and 9 times out of 10 you may be able to set it up to ship your quarter to him so he can research it and tell you what you have and what the value can bring and sometimes he does offer to buy it outright from the person. Also know that this info is only from what I have read about your quarter so I would really hate for you to get excited and find out it was just a tarnished planchet but hey, you never know. Keep me posted.