1/9 tintype of a boy, possibly in uniform. It looks like his hand it resting on some object off to the right that is hidden by the mat. On the back is a Civil War tax stamp. 

Tintype is behind mat and cover glass in half of a case. Light mat abrasions. Under magnification that white stuff looks like it could be brushed off of the image if you open it up... it doesn't appear to be corrosion or anything permanent.