I agree with Buckles that this one is probably civilian. Even with backmarks, it is sometimes hard or in other cases impossible to know which were the issued General Staff buttons (1810-1832) , and which ones were civilian. Because of this, as Buckles says, they ofen get bunched into the civilian category, kind of like the tombacs. Your's seems to be about 18mm which could put it in the ballpark for a General Staff, except that it has no backmark that is visible, and so would be impossible to positively identify.