It's quite common to see Roosevelt dimes struck a little off center but this caught my eye due to the extra ridges. The reverse shows that it is off center but there are no extra ridges showing. Is this considered an error coin? If so how common is it?
Your coin shows the result of a collar clash. At one time the obverse die was misallingned far enough the the edge of the die that forms the top surface of the rim clashed against the edge of the collar and picked up clashmarks showing the top edge of the reeding. Now that it is back closer to the proper place the clashmarks give it the appearance of a second set of reeds on the top edge of the rim. They are fairly common.
