From the looks of it, it seems to be made of two types of metal. The blue crystals would indicate a copper oxide (cupric sulfate maybe) The lack of corrosion on that surface also indicated copper (brass) and the lack of bronze disease says it's probably not real old (maybe 100 years or so). The other corrosion - black/brown indicates it probably had some iron parts. The two "ears" may be what's left of the iron part of the lock and the big "blob" in the middle may be the keyhole that had the key until it corroded away. It is now a big, hard, piece of crud.
So my guess is that it is an old decorated lock for a small box. Something that may have held coffee, sugar, or something else in plain sight and the lock had to look more formal that a lock for the barn door.
Do you have access to any electrolysis? That might help. Also, a good soak in WD-40 can loosen the crud so it will come off "fairly" easily. Might help reveal enough to know more.
Daryl
