This button is one of the few exceptions to the rule that says if a button has a wide-rim, it is post-Civil War. According to both Warren Tice and Dan Binder, this staff button was manufactured starting around 1860 and production continued throughout the war. The D. Evans backmark is correct. I don't know if these buttons were widely used or if they were well-received by officers. But one thing is sure. This style set the standard for most military buttons from 1866 almost through the Spanish-American War.

 

But this one is DEFINITELY appropriate in a Civil War collection.

 

Condition is excellent - full gilt, clear backmark, straight & solid shank. Price is almost half what a lot of other "staffs" are selling for.