I just sent a 1970 D Washington Quarter to ANACS for slabbing. It's very thin and appears to be struck on a dime planchet, so i'm assuming its and error. Its a circulated coin in good shape and was my dads, who probably took it out of circulation in the late 70's or early 80's. Thanks, Harry
It's a neat error and is fairly common on the '70-D. There were also a lot on the '71-D but these are far more infrequently seen and they have been reported on the '72-D. In those days the Denver mint was using a new system where they passed strip through a slit in the wall to the blanking presses which punched the planchet from it. Communication was sometimes faulty and when quarter strip was desired they might actually get dime strip. This material is pretty strong in strip form and is handled by machine so the operators might not notice the error. The quarter sized planchets struck from dime stock would sometimes end up on the stamping floor and thin quarters result. These were a pain back in 1970/ '71 since they don't work in machines. Many would be thrown in the garbage in frustration. There were so many of them that saving them just seemed a waste. In retrospect it was probably no more than a quarter million and possibly substantially fewer. These coins have never circulated because they don't work in machines so almost all of them are in XF/ AU with a few uncs around. They sell for 10 to 20 dollars on eBay now days. They're pretty neat coins but you couldn't get me to say that in 1970.
First of all do you have a picture of the coin in question? It would also be a good idea to start a new thread, and ANACS is a third party grading service.